Determination of the resistance to hydrocarbon pool fires of fire protection materials and systems for pressure vessels

This document specifies a test method for determining the fire resistance of pressure vessels with a fire protection system when subjected to standard fire exposure conditions. It does not address vessels cooled by water deluge or water monitor. The test data thus obtained permits subsequent classification on the basis of the duration for which the performance of the pressure vessel under these conditions satisfies specified criteria. The design of the pressure vessel is not covered in this document.

Détermination de la résistance aux feux de nappe d'hydrocarbure des matériaux et systèmes de protection incendie des récipients sous pression

General Information

Status
Published
Publication Date
12-Jan-2023
Current Stage
6060 - International Standard published
Start Date
13-Jan-2023
Due Date
24-Jul-2023
Completion Date
13-Jan-2023
Ref Project

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INTERNATIONAL ISO
STANDARD 21843
Second edition
2023-01
Determination of the resistance
to hydrocarbon pool fires of fire
protection materials and systems for
pressure vessels
Détermination de la résistance aux feux de nappe d'hydrocarbure
des matériaux et systèmes de protection incendie des récipients sous
pression
Reference number
ISO 21843:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 21843:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 21843:2023(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 3

5 Principle ........................................................................................................................................................................................................................ 4

6 Test equipment ......................................................................................................................................................................................................4

6.1 General ........................................................................................................................................................................................................... 4

6.2 Burner arrangement ........................................................................................................................................... ............................... 5

6.3 Fuel supply for burners ................................................................................................................................................................... 5

6.4 Test fluids .................................................................................................................................................................................................... 5

6.5 Test building ............................................................................................................................................................................................. 5

7 Calibration tests ................................................................................................................................................................................................... 5

7.1 General requirements ...................................................................................................................................................................... 5

7.2 Calibration test vessel construction .................................................................................................................................... 6

7.3 Calibration test procedure ........................................................................................................................................................... 7

7.4 Analysis of test data ........................................................................................................................................................................... 9

7.5 Requirements for successful calibration tests ........................................................................................................... 9

7.6 Environmental conditions ......................................................................................................................................................... 10

7.7 Tolerances ................................................................................................................................................................................................ 10

7.8 Calibration and test report ....................................................................................................................................................... 11

8 Construction of fire test specimens ..............................................................................................................................................12

9 Instrumentation ................................................................................................................................................................................................12

10 Fire protection materials and systems .....................................................................................................................................14

10.1 General ........................................................................................................................................................................................................ 14

10.2 Applied fire protection materials ....................................................................................................................................... 14

10.3 Assemblies and mounted fire protection systems .............................................................................................. 16

11 Test procedure ....................................................................................................................................................................................................16

12 Termination of the test...............................................................................................................................................................................17

13 Repeatability and reproducibility .................................................................................................................................................17

14 Uncertainty of measurement ...............................................................................................................................................................17

15 Test report ...............................................................................................................................................................................................................17

16 Practical application of test results ..............................................................................................................................................18

16.1 Pressure relief valve (PRV) ...................................................................................................................................................... 18

16.2 Propane (or alternative test fluid) fill level ............................................................................................................... 19

17 Performance criteria ....................................................................................................................................................................................19

17.1 General ........................................................................................................................................................................................................ 19

17.2 Substrate temperature ................................................................................................................................................................. 19

17.3 Coatings and spray-applied materials ............................................................................................................................ 19

17.4 Systems and assemblies .............................................................................................................................................................. 20

18 Factors affecting the validity of the test ..................................................................................................................................20

18.1 Interruption of the test ................................................................................................................................................................20

18.2 Failure of TCs and DFTs ............................................................................................................................................................... 20

18.3 Failure of pressure transducers ........................................................................................................................................... 21

18.4 Test-related tube and pipe ......................................................................................................................................................... 21

iii
© ISO 2023 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 21843:2023(E)

18.5 Variation in environmental conditions .......................................................................................................................... 21

18.6 Directional flame thermometer (DFT) results ....................................................................................................... 21

19 Recommended classification procedures ..............................................................................................................................22

19.1 General ........................................................................................................................................................................................................22

19.2 Type of fire .............................................................................................................................................................................................. 22

19.3 Type of application ........................................................................................................................................................................... 22

19.4 Classification based on temperature rise and period of resistance ....................................................22

19.5 Classification based on duration before failure ..................................................................................................... 22

Annex A (informative) Example piping and instrumentation diagram for test facility ............................23

Annex B (informative) Directional flame thermometers (DFTs) .......................................................................................25

Annex C (normative) Method of affixing thermocouples ............................................................................................................26

Annex D (informative) Radiation-convection (R-C) balance ..................................................................................................27

Annex E (informative) Additional classification procedures: Classification based on

duration before failure ........................................................................................................................................... ....................................29

Bibliography .............................................................................................................................................................................................................................34

© ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 21843:2023(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire

containment.

This second edition cancels and replaces the first edition (ISO 21843:2018), which has been technically

revised.
The main changes are as follows:
— the calibration conditions have been modified;
— an alternative method for confirming test conditions has been provided.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 21843:2023(E)
Introduction

This document describes a test procedure for assessing the protection afforded by fire protection

materials and systems to pressure vessels. It gives an indication of how fire protection materials

perform when exposed to a set of specified fire conditions. Actual vessels can vary in construction from

that tested and can utilize additional protection systems. The test conditions have been shown to be

representative of the severity of unconfined pool fires fuelled by light and medium oil distillates such as

liquefied petroleum gas (LPG) and petroleum products.
© ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 21843:2023(E)
Determination of the resistance to hydrocarbon pool fires
of fire protection materials and systems for pressure
vessels
1 Scope

This document specifies a test method for determining the fire resistance of pressure vessels with a

fire protection system when subjected to standard fire exposure conditions. It does not address vessels

cooled by water deluge or water monitor. The test data thus obtained permits subsequent classification

on the basis of the duration for which the performance of the pressure vessel under these conditions

satisfies specified criteria. The design of the pressure vessel is not covered in this document.

2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
blowdown valve
BDV
blowdown device
valve or device that opens to depressurize a pressure vessel
EXAMPLE Fusible plug.
3.2
burner arrangement

configuration of the equipment designed to engulf the test specimen in fire, with specific reference to

the size, orientation, frequency and spacing of burner heads, and the design of fuel supply piping

3.3
burst pressure
calculated burst pressure

pressure at which the vessel is expected to fail based on the known vessel and material

properties and the peak wall temperatures

Note 1 to entry: The burst pressure depends on how quickly and severely the vessel is heated. One approximate

estimate of the burst pressure is that pressure that gives a hoop stress equal to the yield strength of the vessel

material at the specific wall temperature of interest.

Note 2 to entry: Other failure criteria can be more appropriate. For long duration tests, high temperature stress

rupture analysis is also considered a realistic failure mode.
© ISO 2023 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 21843:2023(E)
3.4
calibration test

test performed by the laboratory prior and separate to customer tests, to confirm that the chosen burner

arrangement in combination with the desired test specimen conforms to the required conditions of this

document
3.5
critical pressure

pressure calculated for a given critical wall temperature as the burst pressure divided by a factor of

safety (FOS)
3.6
critical temperature

design limiting temperature, or a specified limiting wall temperature, that the vessel wall temperature

is required not to exceed during fire exposure

Note 1 to entry: This temperature is related to a factor of safety (FOS) for the vessel when exposed to fire.

3.7
directional flame thermometer
DFT

passive thermocouple-based sensor that can be used for the estimation of the fire-effective blackbody

temperature and radiation convection balance

Note 1 to entry: Various designs are available. A simple design is described in this document.

3.8
factor of safety
FOS

ratio of the actual burst pressure of the vessel at the temperature of interest (e.g. critical temperature)

divided by the actual working pressure in the vessel

Note 1 to entry: A typical FOS at ambient temperature conditions is in the range of 2 to 3.

3.9
fire protection system
thermal protection system

protection afforded to the vessel to reduce the rate of heat transfer from the fire to the vessel, throughout

the period of exposure to fire, including any protection materials together with any encasement (such

as a jacket), and supporting system (such as mesh reinforcement or a framing system) and any specified

primer and top coat if applicable

Note 1 to entry: Often referred to as a thermal protection system in North America.

3.10
pool fire

hydrocarbon diffusion fire that occurs over a static or flowing release of flammable liquids

Note 1 to entry: It simulates large turbulent diffusion flames that are strongly radiating.

3.11
pressure relief valve
pressure safety valve
PRV
pressure-activated valve intended to limit pressure rise to a specified value
Note 1 to entry: These valves have set opening and reclosing pressures.
© ISO 2023 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 21843:2023(E)
3.12
pressure vessel

vessel capable of containing pressures significantly above ambient, even if normal operational

procedure does not involve pressure rise above ambient
Note 1 to entry: Pressure vessels are often referred to as vessels or tanks.
3.13
radiation-convection balance

fraction or percentage of the total heat transfer to a cool surface that is due to thermal radiation

Note 1 to entry: The cool surface may be a water-cooled calorimeter at a temperature of under 120 °C.

3.14
test-related tube and pipe

additional tube or pipe added to the vessel for the purposes of performing the tests

Note 1 to entry: These can potentially not be present on the real application vessel.

3.15
vessel shell
primary wall of the vessel
4 Symbols
ΔT vessel shell temperature, at time m, assumed to be equal to ΔT
S,m w,m
ΔT result of T − T
w,m w,m w,0
A surface area of vessel shell
c specific heat capacity of steel
c specific heat capacity of water
e Euler's number
f radiation fraction
rad
h convection heat transfer coefficient
L length
L intermediate length
int
m mass of steel
m mass of water
P pressure
P measured pressure
P burst pressure based on the ultimate tensile strength
P burst pressure based on the yield strength
q convection component (heat flux due to convection)
conv
q net heat flux
net
© ISO 2023 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 21843:2023(E)
q radiation component (heat flux due to radiation)
rad
r radius
T ambient temperature
amb
T calorimeter temperature
cal
T directional flame thermometer temperature
DFT
T flame temperature
T temperature of thermocouple n at time m.
n,m
T average water temperature at time m;
w,m
t time
t duration of test (time of termination)
mean average
ε fire emissivity
ε surface emissivity
−8 −2 −4
σ Stefan-Boltzmann constant (5,67 × 10 W·m ·K )
t time
5 Principle

The method described in this document provides an indication of how vessels protected with fire

protection materials or systems perform when exposed to pool fires on solid surfaces. It simulates the

thermal loads to a vessel engulfed in a large pool fire through the use of burners to create a flame

capable of engulfing a vessel. To ensure that suitable test conditions are achieved and maintained, it

describes calibration tests to be performed prior to fire testing, sets permitted tolerances from the

calibrated set-up, and delimits environmental conditions.
6 Test equipment
6.1 General

The test procedure is intended to simulate a liquid hydrocarbon pool fire that achieves a steady heat

2 2
flux to a cool surface of 90 kW/m to 120 kW/m over a specified period of time.

NOTE Literature suggests that heat flux to a cool surface in a large liquid hydrocarbon pool fire is 80 % to

90 % due to thermal radiation and the remainder is by convection.

An example piping and instrumentation diagram for a vessel testing facility is shown in Annex A. Test

equipment employed in the conduct of the test consists essentially of the following:

a) a specially designed burner arrangement to subject the test specimen to the conditions specified in

the calibration section;
b) propane storage capable of fuelling the test for the required duration;
c) equipment to control and monitor the propane flow rate throughout the test;
d) equipment to vent and purge the vessel after testing.
© ISO 2023 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 21843:2023(E)

Test laboratories should be aware of the significant potential hazards involved in pressure vessels

testing. Facilities intending to undertake tests in accordance with this document should be designed to

be safe in the event of vessel failure.
6.2 Burner arrangement

This test procedure uses liquid-propane-fuelled burners to simulate a pool fire. Burners are used

because they provide more control over the test conditions. The burner system shall be designed to

produce a low momentum and luminous fire of sufficient thickness so that the resulting heat flux is

predominantly by radiation (i.e. radiation fraction greater than 75 %).

To simulate pool fire conditions a burner system shall be used. Burners shall be designed to achieve

total engulfment and uniformity of heating and shall be present on all four sides and both ends of the

vessel. The maximum nozzle spacing shall be no greater than 0,5 m.

The burner design can be varied by the test laboratory to meet the calibration requirements; for

informative purposes, an example of burner design is shown in Annex A.

The burner arrangement shall be designed to receive equal mass flow rates of propane to two

diametrically opposite locations at the ends of the vessel to ensure broadly symmetrical heating.

The supply line length and fittings shall also be designed to ensure equal propane flow to the burner

arrangement and all supply lines. Cooling of the supply shall be provided as necessary to protect the

burner supply for the duration of the test. The burner system shall be designed to ensure stabilization

of the fuel flow rate and stabilization of the flame temperatures [as defined by directional flame

thermometers (DFTs) in Clause 9 and Annex B] within 2 min of the flame ignition and test commencing.

6.3 Fuel supply for burners

The burner system fuel shall be commercial propane or LPG. The fuel supply shall be capable of

delivering up to 1,2 kg/s to the burner arrangement and controlling the flow rate to within ±0,05 kg/s

of the target flow rate as determined by calibration testing.
6.4 Test fluids

The test fluid for the test vessel shall be commercial propane or LPG or any other fluid specified by the

sponsor. Means of filling the test vessel (including air purge) prior to a test, and purging the vessel after

the test to allow safe inspection, shall be provided. Equipment to pump or push liquid propane from

the test vessel back to a storage vessel after the test may be utilized. A means of determining the total

propane loss from the test vessel throughout the test shall be available.
6.5 Test building

Large-scale exterior fire tests are subject to environmentally-induced variations due to wind. Stricter

tolerances in deviation from the as-tested environmental conditions are imposed for testing if the test

is not protected from the environment through the use of an enclosure in the form of a shed or building.

These tolerances are described in 7.7.

If used, environmental protection shall be suitably enclosed on all four sides and have full roof coverage.

Openings for ventilation shall be equally distributed and sized, so far as is practicable.

7 Calibration tests
7.1 General requirements

Due to the variations involved in external large-scale testing, it is required to successfully perform

three calibration tests before a particular fire burner system and test configuration is considered

suitable as the basis for fire testing.
© ISO 2023 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 21843:2023(E)

The net heat flux to a water-filled vessel shall be determined and DFTs shall be used to assess both

the uniformity of heating and the radiation-convection balance. A thermal imager shall also be used to

confirm uniformity of heating and radiation-convection balance in the calibration tests. See Annex D for

methods to estimate the radiation-convection balance. All three tests shall be performed in accordance

with 7.2 and 7.3 and shall use the same vessel, burner configurations and test parameters.

The calibration test results shall be assessed in accordance with 7.4. Once a test configuration has

met the requirements in 7.5, it shall be considered suitable for testing of actual test specimens in

environmental conditions as defined in 7.6. The tolerances in variation from the calibration test set up

during actual fire testing are given in 7.7.

Calibration testing should be repeated in the event of any modifications to the test specimen beyond

the permitted tolerances in 7.7, any modifications to the burner or nozzle arrangement or propane flow

rate, any significant modifications to the test equipment or test building, or any departure from the

environmental conditions as defined in 7.6.

Calibration tests shall be performed at least every three years, even in the event of no changes as

listed above, to ensure equipment functions as intended. Calibration test results shall be written

up as calibration reports as described in 7.8 and retained by the test laboratory for reference when

conducting future fire tests.
7.2 Calibration test vessel construction

The calibration vessel shall be manufactured according to appropriate pressure vessel regulations. It

shall have a minimum diameter of 1 200 mm, and a minimum length of 2 000 mm. The vessel shall be

supported on two steel saddles, which shall be insulated or water-cooled. No fire protection materials

or system shall be installed on the calibration vessel shell.

An appropriately sized vent shall be cut at the top of the vessel to permit extraction of thermocouples

(TCs) and to prevent pressurization during calibration testing. An agitator shall be i

...

ISO/TC 92/SC 2/WG12 N 050
Date: 2022-06-0911
ISO 21843:2022(E)
ISO/TC 92/SC 2/WG 12
Secretariat: ANSI

Determination of the resistance to hydrocarbon pool fires of fire protection materials

and systems for pressure vessels

Détermination de la résistance aux feux de nappe d'hydrocarbure des matériaux et systèmes de

protection incendie des récipients sous pression
---------------------- Page: 1 ----------------------
ISO/DIS 21843:2022(E)
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation,

no part of this publication may be reproduced or utilized otherwise in any form or by any means,

electronic or mechanical, including photocopying, or posting on the internet or an intranet,

without prior written permission. Permission can be requested from either ISO at the address

below or ISO's member body in the country of the requester.
ISO Copyright Office
CP 401 • CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
iiii © ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 21843:2022(E)
Contents

Foreword ........................................................................................................................................................................... v

Introduction ................................................................................................................................................................... vi

1 Scope .................................................................................................................................................................... 1

2 Normative references .................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................... 1

4 Symbols ............................................................................................................................................................... 3

5 Principle .............................................................................................................................................................. 5

6 Test equipment................................................................................................................................................. 5

6.1 General ................................................................................................................................................................ 5

6.2 Burner arrangement ...................................................................................................................................... 5

6.3 Fuel supply for burners ................................................................................................................................. 6

6.4 Test fluids ........................................................................................................................................................... 6

6.5 Test building ...................................................................................................................................................... 6

7 Calibration tests ............................................................................................................................................... 6

7.1 General requirements .................................................................................................................................... 6

7.2 Calibration test vessel construction ......................................................................................................... 7

7.3 Calibration test procedure ........................................................................................................................ 10

7.4 Analysis of test data ..................................................................................................................................... 11

7.5 Requirements for successful calibration tests ................................................................................... 12

7.6 Environmental conditions ......................................................................................................................... 13

7.7 Tolerances ....................................................................................................................................................... 13

7.8 Calibration and test report........................................................................................................................ 14

8 Construction of fire test specimens........................................................................................................ 15

9 Instrumentation ............................................................................................................................................ 16

10 Fire protection materials and systems ................................................................................................. 18

10.1 General ............................................................................................................................................................. 18

10.2 Applied fire protection materials ........................................................................................................... 19

10.3 Assemblies and mounted fire protection systems ........................................................................... 21

11 Test procedure .............................................................................................................................................. 21

12 Termination of the test ............................................................................................................................... 22

13 Repeatability and reproducibility .......................................................................................................... 22

14 Uncertainty of measurement.................................................................................................................... 22

15 Test report ...................................................................................................................................................... 22

16 Practical application of test results ....................................................................................................... 24

16.1 Pressure relief valve (PRV) ....................................................................................................................... 24

16.2 Propane (or alternative test fluid) fill level ........................................................................................ 24

17 Performance criteria ................................................................................................................................... 24

17.1 General ............................................................................................................................................................. 24

17.2 Substrate temperature ............................................................................................................................... 24

17.3 Coatings and spray-applied materials .................................................................................................. 25

17.4 Systems and assemblies ............................................................................................................................. 25

© ISO 2022 – All rights reserved iiiiii
---------------------- Page: 3 ----------------------
ISO/DIS 21843:2022(E)

18 Factors affecting the validity of the test ............................................................................................... 25

18.1 Interruption of the test .............................................................................................................................. 25

18.2 Failure of TCs and DFTs ............................................................................................................................. 26

18.3 Failure of pressure transducers ............................................................................................................. 26

18.4 Test-related tube and pipe ....................................................................................................................... 26

18.5 Variation in environmental conditions ................................................................................................ 26

18.6 Directional flame thermometer (DFT) results .................................................................................. 26

19 Recommended classification procedures ........................................................................................... 27

19.1 General ............................................................................................................................................................. 27

19.2 Type of fire ...................................................................................................................................................... 27

19.3 Type of application ...................................................................................................................................... 27

19.4 Classification based on temperature rise and period of resistance .......................................... 28

19.5 Classification based on duration before failure ................................................................................ 28

Annex A (informative) Example piping and instrumentation diagram for test facility ................... 29

Annex B (informative) Directional flame thermometers (DFTs)............................................................. 31

Annex C (normative) Method of affixing thermocouples ............................................................................ 33

Annex D (informative) Radiation-convection (R-C) balance ..................................................................... 35

Annex E (informative) Additional classification procedures: Classification based on

duration before failure .............................................................................................................................. 37

Bibliography ................................................................................................................................................................. 44

iviv © ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/DIS 21843:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national

standards bodies (ISO member bodies). The work of preparing International Standards is normally

carried out through ISO technical committees. Each member body interested in a subject for which a

technical committee has been established has the right to be represented on that committee.

International organizations, governmental and non-governmental, in liaison with ISO, also take part in

the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all

matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire

containment.

This second edition cancels and replaces the first edition (ISO 21843:2018), which has been technically

revised.
The main changes are as follows:
— modification tothe calibration conditions have been modified;

- Provision of— an alternative method to confirmfor confirming test conditions has been provided.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved vv
---------------------- Page: 5 ----------------------
ISO/DIS 21843:2022(E)
Introduction

This document describes a test procedure to assessfor assessing the protection afforded by fire

protection materials and systems to pressure vessels. It gives an indication of how fire protection

materials perform when exposed to a set of specified fire conditions. Actual vessels can vary in

construction from that tested and can utilize additional protection systems. The test conditions have

been shown to be representative of the severity of unconfined pool fires fuelled by light and medium oil

distillates such as liquefied petroleum gas (LPG) and petroleum products.
vivi © ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 21843:2022(E)
Determination of the resistance to hydrocarbon pool fires of fire
protection materials and systems for pressure vessels
1 Scope

This document specifies a test method for determining the fire resistance of pressure vessels with a fire

protection system when subjected to standard fire exposure conditions. It does not address vessels

cooled by water deluge or water monitor. The test data thus obtained permits subsequent classification

on the basis of the duration for which the performance of the pressure vessel under these conditions

satisfies specified criteria. The design of the pressure vessel is not covered in this document.

2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
blowdown valve
BDV
blowdown device
valve or device that opens to depressurize a pressure vessel
EXAMPLE Fusible plug.
3.2
burner arrangement

configuration of the equipment designed to engulf the test specimen in fire, with specific reference to

the size, orientation, frequency and spacing of burner heads, and the design of fuel supply piping

3.3
burst pressure
calculated burst pressure

pressure at which the vessel is expected to fail based on the known vessel and material

properties and the peak wall temperatures

Note 1 to entry: The burst pressure depends on how quickly and severely the vessel is heated. One approximate

estimate of the burst pressure is that pressure that gives a hoop stress equal to the yield strength of the vessel

material at the specific wall temperature of interest.
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ISO/DIS 21843:2022(E)

Note 2 to entry: Other failure criteria can be more appropriate. For long duration tests, high temperature stress

rupture analysis is also considered a realistic failure mode.
3.4
calibration test

test performed by the laboratory prior and separate to customer tests, to confirm that the chosen

burner arrangement in combination with the desired test specimen conforms to the required conditions

of this document
3.5
critical pressure

pressure calculated for a given critical wall temperature as the burst pressure divided by a factor of

safety (FOS)
3.6
critical temperature

design limiting temperature, or a specified limiting wall temperature, that the vessel wall temperature

is required not to exceed during fire exposure

Note 1 to entry: This temperature is related to a factor of safety (FOS) for the vessel when exposed to fire.

3.7
directional flame thermometer
DFT

passive thermocouple-based sensor that can be used for the estimation of the fire-effective black

bodyblackbody temperature and radiation convection balance

Note 1 to entry: Various designs are available. A simple design is described in this document.

3.8
factor of safety
FOS

ratio of the actual burst pressure of the vessel at the temperature of interest (e.g. critical temperature)

divided by the actual working pressure in the vessel

Note 1 to entry: A typical FOS at ambient temperature conditions is in the range of 2 to 3.

3.9
fire protection system
thermal protection system

protection afforded to the vessel to reduce the rate of heat transfer from the fire to the vessel,

throughout the period of exposure to fire, including any protection materials together with any

encasement (such as a jacket), and supporting system (such as mesh reinforcement or a framing

system) and any specified primer and top coat if applicable

Note 1 to entry: Often referred to as a thermal protection system in North America.

3.10
pool fire

hydrocarbon diffusion fire that occurs over a static or flowing release of flammable liquids

Note 1 to entry: It simulates large turbulent diffusion flames that are strongly radiating.

3.11
pressure relief valve
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ISO/DIS 21843:2022(E)
pressure safety valve
PRV
pressure-activated valve intended to limit pressure rise to a specified value
Note 1 to entry: These valves have set opening and reclosing pressures.
3.12
pressure vessel

vessel capable of containing pressures significantly above ambient, even if normal operational

procedure does not involve pressure rise above ambient
Note 1 to entry: Pressure vessels are often referred to as vessels or tanks.
3.13
radiation-convection balance

fraction or percentage of the total heat transfer to a cool surface that is due to thermal radiation

Note 1 to entry: The cool surface may be a water-cooled calorimeter at a temperature of under 120 °C.

3.14
test-related tube and pipe

additional tube or pipe added to the vessel for the purposes of performing the tests

Note 1 to entry: TheyThese can potentially not be present on the real application vessel.

3.15
vessel shell
primary wall of the vessel
4 Symbols and abbreviated terms
ΔT vessel shell temperature, at time m, assumed to be equal to ΔT
S,m w,m
ΔT result of T − T
w,m w,m w,0
AA surface area of vessel shell
c specific heat capacity of steel
c specific heat capacity of water
e Euler's number
f radiation fraction
rad
Th temperatureconvection heat transfer coefficient
t time
t L termination lengthtime
Lint intermediate length
mm mass of steel
q m mass of waternet absorbed heat flux (W·m )
net w
P pressure
P measured pressure
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ISO/DIS 21843:2022(E)
P burst pressure based on the ultimate tensile strength
P burst pressure based on the yield strength
q convection component (heat flux due to convection)
conv
q net heat flux
net
q radiation component (heat flux due to radiation)
rad
εr radiusemissivity
−8 −2 −4
T σ ambient temperatureStefan-Boltzmann constant (5,67 × 10 W·m ·K )
amb
Subscript terms
T cal calorimeter temperature
cal
T DFT directional flame thermometer temperature
DFT
f fire
indic indicated
S Substrate
r radius
ΔT T is the vessel shellflame temperature, assumed equal to ΔTw,t (°C);
s,t f
ΔT is the result of Tw,t − Tw,0 (°C);
w,t
m is the mass of steel (kg);
mw is the mass of water (kg);
c is the specific heat capacity of steel (J·kg−1·K−1);
c is the specific heat capacity of water (J·kg−1 ·K−1);

t T is the durationtemperature of test (thermocouple n at time of termination) (s);m.

t n,m
A is the surface area of vessel shell (m2).
T is the average water temperature at time tm;
w,tm
t time
T t is the temperatureduration of Thermocouple n at test (time t.of termination)
n,t T
denotes the mean average
ambient temperature
X T
amb
calorimeter temperature
cal
directional flame thermometer temperature
TDFT
ε fire emissivity
ε surface emissivity
−8 −2 −4
σ Stefan-Boltzmann constant (5,67 × 10 W·m ·K )
t time
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ISO/DIS 21843:2022(E)
5 Principle

The method described in this document provides an indication of how vessels protected with fire

protection materials or systems perform when exposed to pool fires on solid surfaces. It simulates the

thermal loads to a vessel engulfed in a large pool fire through the use of burners to create a flame

capable of engulfing a vessel. To ensure that suitable test conditions are achieved and maintained, it

describes calibration tests to be performed prior to fire testing, sets permitted tolerances from the

calibrated set-up, and delimits environmental conditions.
6 Test equipment
6.1 General

The test procedure is intended to simulate a liquid hydrocarbon pool fire that achieves a steady heat

2 2
flux to a cool surface of 90 kW/m to 120 kW/m over a specified period of time.

NOTE The literatureLiterature suggests that heat flux to a cool surface in a large liquid hydrocarbon pool fire is

80 % to 90 % due to thermal radiation and the remainder is by convection.

An example piping and instrumentation diagram for a vessel testing facility is shown in Annex A. Test

equipment employed in the conduct of the test consists essentially of the following:

a) a specially designed burner arrangement to subject the test specimen to the conditions specified in

the calibration section;
b) propane storage capable of fuelling the test for the required duration;
c) equipment to control and monitor the propane flow rate throughout the test;
d) equipment to vent and purge the vessel after testing.

Test laboratories should be aware of the significant potential hazards involved in pressure vessels

testing. Facilities intending to undertake tests in accordance with this document should be designed to

be safe in the event of vessel failure.
6.2 Burner arrangement

This test procedure uses liquid -propane -fuelled burners to simulate a pool fire. Burners are used

because they provide more control over the test conditions. The burner system shall be designed to

produce a low momentum and luminous fire of sufficient thickness so that the resulting heat flux is

predominantly by radiation (i.e. radiation fraction greater than 75 %).

To simulate pool fire conditions a burner system shall be used. Burners shall be designed to achieve

total engulfment and uniformity of heating and shall be present on all four sides and both ends of the

vessel. The maximum nozzle spacing shall be no greater than 0,5 m.

The burner design can be varied by the test laboratory to meet the calibration requirements; for

informative purposes, an example of burner design is shown in Annex A.

The burner arrangement shall be designed to receive equal mass flow rates of propane to two

diametrically opposite locations at the ends of the vessel to ensure broadly symmetrical heating. The

supply line length and fittings shall also be designed to ensure equal propane flow to the burner

arrangement and all supply lines. Cooling of the supply shall be provided as necessary to protect the

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ISO/DIS 21843:2022(E)

burner supply for the duration of the test. The burner system shall be designed to ensure stabilization

of the fuel flow rate and stabilization of the flame temperatures [as defined by directional flame

thermometers (DFTs) in Clause 9 and Annex B] within 2 min of the flame ignition and test commencing.

6.3 Fuel supply for burners

The burner system fuel shall be commercial propane or LPG. The fuel supply shall be capable of

delivering up to 1,2 kg/s to the burner arrangement and controlling the flow rate to within ±0,05 kg/s

of the target flow rate as determined by calibration testing.
6.4 Test fluids

The test fluid for the test vessel shall be commercial propane or LPG or any other fluid specified by the

sponsor. Means of filling the test vessel (including air purge) prior to a test, and purging the vessel

subsequent toafter the test to allow safe inspection, shall be provided. Equipment to pump or push

liquid propane from the test vessel back to a storage vessel after the test may be utilized. A means of

determining the total propane loss from the test vessel throughout the test shall be available.

6.5 Test building

Large-scale exterior fire tests are subject to environmentally-induced variations due to wind. Stricter

tolerances in deviation from the as-tested environmental conditions are imposed for testing if the test is

not protected from the environment through the use of an enclosure in the form of a shed or building.

These tolerances are described in 7.7.

If used, environmental protection shall be suitably enclosed on all four sides and have full roof

coverage. Openings for ventilation shall be equally distributed and sized, so far as is practicable.

7 Calibration tests
7.1 General requirements

Due to the variations involved in external large-scale testing, it is required to successfully perform three

calibration tests before a particular fire burner system and test configuration is considered suitable as

the basis for fire testing.

The net heat flux to a water-filled vessel shall be determined and DFTs shall be used to assess both the

uniformity of heating and the radiation-convection balance. A thermal imager shall also be used to

confirm uniformity of heating and radiation-convection balance in the calibration tests. See Annex D for

methods to estimate the radiation-convection balance. All three tests shall be performed in accordance

with 7.2 and 7.3 and shall use the same vessel, burner configurations and test parameters.

The calibration test results shall be assessed in accordance with 7.4. Once a test configuration has met

the requirements in 7.5, it shall be considered suitable for testing of actual test specimens in

environmental conditions as defined in 7.6. The tolerances in variation from the calibration test set up

during actual fire testing are given in 7.7.

Calibration testing should be repeated in the event of any modifications to the test specimen beyond the

permitted tolerances in 7.7, any modifications to the burner or nozzle arrangement or propane flow

rate, any significant modifications to the test equipment or test building, or any departure from the

environmental conditions as defined in 7.6.

Calibration tests shall be performed at least every three years, even in the event of no changes as listed

above, to ensure equipment functions as intended. Calibration test results shall be written up as

calibration reports as described in 7.8 and retained by the test laboratory for reference when

conducting future fire tests.
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ISO/DIS 21843:2022(E)
7.2 Calibration test vessel construction

The calibration vessel shall be manufactured according to appropriate pressure vessel regulations. It

shall have a minimum diameter of 1 200 mm, and a minimum length of 2 000 mm. The vessel shall be

supported on two steel saddles, which shall be insulated or water-cooled. No fire protection materials

or system shall be installed on the calibration vessel shell.

An appropriately sized vent shall be cut at the top of the vessel to permit extraction of thermocouples

(TCs) and to prevent pressurization during calibration testing. An agitator shall be installed within the

vessel, located close to the middle to mix the water to maintain near uniform temperature. Only

connecting piping required for operation of the agitator is permitted, and this piping may be water-

cooled if necessary. Any covers or guards for gauges and connections shall be removed, and all

remaining connections shall be sealed.

The calibration vessel shell shall be instrumented with 16 DFTs. A simple design of DFTs is given as an

example in Annex B. DFTs shall be attached to the vessel facing out into the fire in locations shown in

Figure 1. Individual TCs that conflict with the position of lifting lugs or fittings may be moved by up to

0,15 m. ThermocouplesTCs that conflict with saddles shall be moved horizontally towards the middle of

the vessel until they are at least 0,25 m from the saddle.

The calibration vessel shall be internally instrumented with 10 insulated type k thermocouplesTCs

(1,5 mm minimum diameter, 3 mm maximum diameter) for measurement of the water temperatur

...

INTERNATIONAL ISO
STANDARD 21843
Second edition
Determination of the resistance
to hydrocarbon pool fires of fire
protection materials and systems for
pressure vessels
Détermination de la résistance aux feux de nappe d'hydrocarbure
des matériaux et systèmes de protection incendie des récipients sous
pression
PROOF/ÉPREUVE
Reference number
ISO 21843:2022(E)
© ISO 2022
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ISO 21843:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO 21843:2022(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 3

5 Principle ........................................................................................................................................................................................................................ 4

6 Test equipment ......................................................................................................................................................................................................4

6.1 General ........................................................................................................................................................................................................... 4

6.2 Burner arrangement ........................................................................................................................................... ............................... 5

6.3 Fuel supply for burners ................................................................................................................................................................... 5

6.4 Test fluids .................................................................................................................................................................................................... 5

6.5 Test building ............................................................................................................................................................................................. 5

7 Calibration tests ................................................................................................................................................................................................... 5

7.1 General requirements ...................................................................................................................................................................... 5

7.2 Calibration test vessel construction .................................................................................................................................... 6

7.3 Calibration test procedure ........................................................................................................................................................... 7

7.4 Analysis of test data ........................................................................................................................................................................... 9

7.5 Requirements for successful calibration tests ........................................................................................................... 9

7.6 Environmental conditions ......................................................................................................................................................... 10

7.7 Tolerances ................................................................................................................................................................................................ 10

7.8 Calibration and test report ....................................................................................................................................................... 11

8 Construction of fire test specimens ..............................................................................................................................................12

9 Instrumentation ................................................................................................................................................................................................12

10 Fire protection materials and systems .....................................................................................................................................14

10.1 General ........................................................................................................................................................................................................ 14

10.2 Applied fire protection materials ....................................................................................................................................... 15

10.3 Assemblies and mounted fire protection systems .............................................................................................. 16

11 Test procedure ....................................................................................................................................................................................................16

12 Termination of the test...............................................................................................................................................................................17

13 Repeatability and reproducibility .................................................................................................................................................17

14 Uncertainty of measurement ...............................................................................................................................................................17

15 Test report ...............................................................................................................................................................................................................17

16 Practical application of test results ..............................................................................................................................................18

16.1 Pressure relief valve (PRV) ...................................................................................................................................................... 18

16.2 Propane (or alternative test fluid) fill level ............................................................................................................... 19

17 Performance criteria ....................................................................................................................................................................................19

17.1 General ........................................................................................................................................................................................................ 19

17.2 Substrate temperature ................................................................................................................................................................. 19

17.3 Coatings and spray-applied materials ............................................................................................................................ 19

17.4 Systems and assemblies .............................................................................................................................................................. 20

18 Factors affecting the validity of the test ..................................................................................................................................20

18.1 Interruption of the test ................................................................................................................................................................20

18.2 Failure of TCs and DFTs ............................................................................................................................................................... 20

18.3 Failure of pressure transducers ........................................................................................................................................... 21

18.4 Test-related tube and pipe ......................................................................................................................................................... 21

iii
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ISO 21843:2022(E)

18.5 Variation in environmental conditions .......................................................................................................................... 21

18.6 Directional flame thermometer (DFT) results ....................................................................................................... 21

19 Recommended classification procedures ..............................................................................................................................22

19.1 General ........................................................................................................................................................................................................22

19.2 Type of fire .............................................................................................................................................................................................. 22

19.3 Type of application ........................................................................................................................................................................... 22

19.4 Classification based on temperature rise and period of resistance ....................................................22

19.5 Classification based on duration before failure ..................................................................................................... 22

Annex A (informative) Example piping and instrumentation diagram for test facility ............................23

Annex B (informative) Directional flame thermometers (DFTs) .......................................................................................25

Annex C (normative) Method of affixing thermocouples ............................................................................................................26

Annex D (informative) Radiation-convection (R-C) balance ..................................................................................................27

Annex E (informative) Additional classification procedures: Classification based on

duration before failure ........................................................................................................................................... ....................................29

Bibliography .............................................................................................................................................................................................................................34

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ISO 21843:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire

containment.

This second edition cancels and replaces the first edition (ISO 21843:2018), which has been technically

revised.
The main changes are as follows:
— the calibration conditions have been modified;
— an alternative method for confirming test conditions has been provided.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 21843:2022(E)
Introduction

This document describes a test procedure for assessing the protection afforded by fire protection

materials and systems to pressure vessels. It gives an indication of how fire protection materials

perform when exposed to a set of specified fire conditions. Actual vessels can vary in construction from

that tested and can utilize additional protection systems. The test conditions have been shown to be

representative of the severity of unconfined pool fires fuelled by light and medium oil distillates such as

liquefied petroleum gas (LPG) and petroleum products.
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INTERNATIONAL STANDARD ISO 21843:2022(E)
Determination of the resistance to hydrocarbon pool fires
of fire protection materials and systems for pressure
vessels
1 Scope

This document specifies a test method for determining the fire resistance of pressure vessels with a

fire protection system when subjected to standard fire exposure conditions. It does not address vessels

cooled by water deluge or water monitor. The test data thus obtained permits subsequent classification

on the basis of the duration for which the performance of the pressure vessel under these conditions

satisfies specified criteria. The design of the pressure vessel is not covered in this document.

2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
blowdown valve
BDV
blowdown device
valve or device that opens to depressurize a pressure vessel
EXAMPLE Fusible plug.
3.2
burner arrangement

configuration of the equipment designed to engulf the test specimen in fire, with specific reference to

the size, orientation, frequency and spacing of burner heads, and the design of fuel supply piping

3.3
burst pressure
calculated burst pressure

pressure at which the vessel is expected to fail based on the known vessel and material

properties and the peak wall temperatures

Note 1 to entry: The burst pressure depends on how quickly and severely the vessel is heated. One approximate

estimate of the burst pressure is that pressure that gives a hoop stress equal to the yield strength of the vessel

material at the specific wall temperature of interest.

Note 2 to entry: Other failure criteria can be more appropriate. For long duration tests, high temperature stress

rupture analysis is also considered a realistic failure mode.
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ISO 21843:2022(E)
3.4
calibration test

test performed by the laboratory prior and separate to customer tests, to confirm that the chosen burner

arrangement in combination with the desired test specimen conforms to the required conditions of this

document
3.5
critical pressure

pressure calculated for a given critical wall temperature as the burst pressure divided by a factor of

safety (FOS)
3.6
critical temperature

design limiting temperature, or a specified limiting wall temperature, that the vessel wall temperature

is required not to exceed during fire exposure

Note 1 to entry: This temperature is related to a factor of safety (FOS) for the vessel when exposed to fire.

3.7
directional flame thermometer
DFT

passive thermocouple-based sensor that can be used for the estimation of the fire-effective blackbody

temperature and radiation convection balance

Note 1 to entry: Various designs are available. A simple design is described in this document.

3.8
factor of safety
FOS

ratio of the actual burst pressure of the vessel at the temperature of interest (e.g. critical temperature)

divided by the actual working pressure in the vessel

Note 1 to entry: A typical FOS at ambient temperature conditions is in the range of 2 to 3.

3.9
fire protection system
thermal protection system

protection afforded to the vessel to reduce the rate of heat transfer from the fire to the vessel, throughout

the period of exposure to fire, including any protection materials together with any encasement (such

as a jacket), and supporting system (such as mesh reinforcement or a framing system) and any specified

primer and top coat if applicable

Note 1 to entry: Often referred to as a thermal protection system in North America.

3.10
pool fire

hydrocarbon diffusion fire that occurs over a static or flowing release of flammable liquids

Note 1 to entry: It simulates large turbulent diffusion flames that are strongly radiating.

3.11
pressure relief valve
pressure safety valve
PRV
pressure-activated valve intended to limit pressure rise to a specified value
Note 1 to entry: These valves have set opening and reclosing pressures.
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ISO 21843:2022(E)
3.12
pressure vessel

vessel capable of containing pressures significantly above ambient, even if normal operational

procedure does not involve pressure rise above ambient
Note 1 to entry: Pressure vessels are often referred to as vessels or tanks.
3.13
radiation-convection balance

fraction or percentage of the total heat transfer to a cool surface that is due to thermal radiation

Note 1 to entry: The cool surface may be a water-cooled calorimeter at a temperature of under 120 °C.

3.14
test-related tube and pipe

additional tube or pipe added to the vessel for the purposes of performing the tests

Note 1 to entry: These can potentially not be present on the real application vessel.

3.15
vessel shell
primary wall of the vessel
4 Symbols
ΔT vessel shell temperature, at time m, assumed to be equal to ΔT
S,m w,m
ΔT result of T − T
w,m w,m w,0
A surface area of vessel shell
c specific heat capacity of steel
c specific heat capacity of water
e Euler's number
f radiation fraction
rad
h convection heat transfer coefficient
L length
L intermediate length
int
m mass of steel
m mass of water
P pressure
P measured pressure
P burst pressure based on the ultimate tensile strength
P burst pressure based on the yield strength
q convection component (heat flux due to convection)
conv
q net heat flux
net
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ISO 21843:2022(E)
q radiation component (heat flux due to radiation)
rad
r radius
T ambient temperature
amb
T calorimeter temperature
cal
T directional flame thermometer temperature
DFT
T flame temperature
T temperature of thermocouple n at time m.
n,m
T average water temperature at time m;
w,m
t time
t duration of test (time of termination)
mean average
ε fire emissivity
ε surface emissivity
−8 −2 −4
σ Stefan-Boltzmann constant (5,67 × 10 W·m ·K )
t time
5 Principle

The method described in this document provides an indication of how vessels protected with fire

protection materials or systems perform when exposed to pool fires on solid surfaces. It simulates the

thermal loads to a vessel engulfed in a large pool fire through the use of burners to create a flame

capable of engulfing a vessel. To ensure that suitable test conditions are achieved and maintained, it

describes calibration tests to be performed prior to fire testing, sets permitted tolerances from the

calibrated set-up, and delimits environmental conditions.
6 Test equipment
6.1 General

The test procedure is intended to simulate a liquid hydrocarbon pool fire that achieves a steady heat

2 2
flux to a cool surface of 90 kW/m to 120 kW/m over a specified period of time.

NOTE Literature suggests that heat flux to a cool surface in a large liquid hydrocarbon pool fire is 80 % to

90 % due to thermal radiation and the remainder is by convection.

An example piping and instrumentation diagram for a vessel testing facility is shown in Annex A. Test

equipment employed in the conduct of the test consists essentially of the following:

a) a specially designed burner arrangement to subject the test specimen to the conditions specified in

the calibration section;
b) propane storage capable of fuelling the test for the required duration;
c) equipment to control and monitor the propane flow rate throughout the test;
d) equipment to vent and purge the vessel after testing.
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ISO 21843:2022(E)

Test laboratories should be aware of the significant potential hazards involved in pressure vessels

testing. Facilities intending to undertake tests in accordance with this document should be designed to

be safe in the event of vessel failure.
6.2 Burner arrangement

This test procedure uses liquid-propane-fuelled burners to simulate a pool fire. Burners are used

because they provide more control over the test conditions. The burner system shall be designed to

produce a low momentum and luminous fire of sufficient thickness so that the resulting heat flux is

predominantly by radiation (i.e. radiation fraction greater than 75 %).

To simulate pool fire conditions a burner system shall be used. Burners shall be designed to achieve

total engulfment and uniformity of heating and shall be present on all four sides and both ends of the

vessel. The maximum nozzle spacing shall be no greater than 0,5 m.

The burner design can be varied by the test laboratory to meet the calibration requirements; for

informative purposes, an example of burner design is shown in Annex A.

The burner arrangement shall be designed to receive equal mass flow rates of propane to two

diametrically opposite locations at the ends of the vessel to ensure broadly symmetrical heating.

The supply line length and fittings shall also be designed to ensure equal propane flow to the burner

arrangement and all supply lines. Cooling of the supply shall be provided as necessary to protect the

burner supply for the duration of the test. The burner system shall be designed to ensure stabilization

of the fuel flow rate and stabilization of the flame temperatures [as defined by directional flame

thermometers (DFTs) in Clause 9 and Annex B] within 2 min of the flame ignition and test commencing.

6.3 Fuel supply for burners

The burner system fuel shall be commercial propane or LPG. The fuel supply shall be capable of

delivering up to 1,2 kg/s to the burner arrangement and controlling the flow rate to within ±0,05 kg/s

of the target flow rate as determined by calibration testing.
6.4 Test fluids

The test fluid for the test vessel shall be commercial propane or LPG or any other fluid specified by the

sponsor. Means of filling the test vessel (including air purge) prior to a test, and purging the vessel after

the test to allow safe inspection, shall be provided. Equipment to pump or push liquid propane from

the test vessel back to a storage vessel after the test may be utilized. A means of determining the total

propane loss from the test vessel throughout the test shall be available.
6.5 Test building

Large-scale exterior fire tests are subject to environmentally-induced variations due to wind. Stricter

tolerances in deviation from the as-tested environmental conditions are imposed for testing if the test

is not protected from the environment through the use of an enclosure in the form of a shed or building.

These tolerances are described in 7.7.

If used, environmental protection shall be suitably enclosed on all four sides and have full roof coverage.

Openings for ventilation shall be equally distributed and sized, so far as is practicable.

7 Calibration tests
7.1 General requirements

Due to the variations involved in external large-scale testing, it is required to successfully perform

three calibration tests before a particular fire burner system and test configuration is considered

suitable as the basis for fire testing.
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ISO 21843:2022(E)

The net heat flux to a water-filled vessel shall be determined and DFTs shall be used to assess both

the uniformity of heating and the radiation-convection balance. A thermal imager shall also be used to

confirm uniformity of heating and radiation-convection balance in the calibration tests. See Annex D for

methods to estimate the radiation-convection balance. All three tests shall be performed in accordance

with 7.2 and 7.3 and shall use the same vessel, burner configurations and test parameters.

The calibration test results shall be assessed in accordance with 7.4. Once a test configuration has

met the requirements in 7.5, it shall be considered suitable for testing of actual test specimens in

environmental conditions as defined in 7.6. The tolerances in variation from the calibration test set up

during actual fire testing are given in 7.7.

Calibration testing should be repeated in the event of any modifications to the test specimen beyond

the permitted tolerances in 7.7, any modifications to the burner or nozzle arrangement or propane flow

rate, any significant modifications to the test equipment or test building, or any departure from the

environmental conditions as defined in 7.6.

Calibration tests shall be performed at least every three years, even in the event of no changes as

listed above, to ensure equipment functions as intended. Calibration test results shall be written

up as calibration reports as described in 7.8 and retained by the test laboratory for reference when

conducting future fire tests.
7.2 Calibration test vessel construction

The calibration vessel shall be manufactured according to appropriate pressure vessel regulations. It

shall have a minimum diameter of 1 200 mm, and a minimum length of 2 000 mm. The vessel shall be

supported on two steel saddles, which shall be insulated or water-cooled. No fire protection materials

or system shall be installed on the calibration vessel shell.
An appropriately sized vent shall be cut at the top of
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