EN ISO 13943:2017

Fire safety - Vocabulary (ISO 13943:2017)

ISO 13943:2017 defines terminology relating to fire safety as used in ISO and IEC fire standards.

Brandschutz - Vokabular (ISO 13943:2017)

Sécurité au feu - Vocabulaire (ISO 13943:2017)

ISO 13943:2017définit la terminologie relative à la sécurité incendie, telle qu'elle est utilisée dans les normes incendie de l'ISO et l'IEC.

Požarna varnost - Slovar (ISO 13943:2017)

Ta dokument določa terminologijo v zvezi s požarno varnostjo, ki se uporablja v protipožarnih standardih ISO in IEC.

Standards Content (sample)

SLOVENSKI STANDARD
SIST EN ISO 13943:2017
01-november-2017
1DGRPHãþD
SIST EN ISO 13943:2011
Požarna varnost - Slovar (ISO 13943:2017)
Fire safety - Vocabulary (ISO 13943:2017)
Brandschutz - Vokabular (ISO 13943:2017)
Sécurité au feu - Vocabulaire (ISO 13943:2017)
Ta slovenski standard je istoveten z: EN ISO 13943:2017
ICS:
01.040.13 Okolje. Varovanje zdravja. Environment. Health
Varnost (Slovarji) protection. Safety
(Vocabularies)
13.220.01 Varstvo pred požarom na Protection against fire in
splošno general
SIST EN ISO 13943:2017 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 13943:2017
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SIST EN ISO 13943:2017
EN ISO 13943
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2017
EUROPÄISCHE NORM
ICS 01.040.13; 13.220.01 Supersedes EN ISO 13943:2010
English Version
Fire safety - Vocabulary (ISO 13943:2017)

Sécurité au feu - Vocabulaire (ISO 13943:2017) Brandschutz - Vokabular (ISO 13943:2017)

This European Standard was approved by CEN on 14 July 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13943:2017 E

worldwide for CEN national Members.
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SIST EN ISO 13943:2017
EN ISO 13943:2017 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 13943:2017
EN ISO 13943:2017 (E)
European foreword

This document (EN ISO 13943:2017) has been prepared by Technical Committee ISO/TC 92 “Fire

safety” in collaboration with Technical Committee CEN/TC 127 “Fire safety in buildings” the secretariat

of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by February 2018, and conflicting national standards

shall be withdrawn at the latest by February 2018.

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

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 13943:2010.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 13943:2017 has been approved by CEN as EN ISO 13943:2017 without any modification.

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SIST EN ISO 13943:2017
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SIST EN ISO 13943:2017
INTERNATIONAL ISO
STANDARD 13943
Third edition
2017-07
Fire safety — Vocabulary
Sécurité au feu — Vocabulaire
Reference number
ISO 13943:2017(E)
ISO 2017
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SIST EN ISO 13943:2017
ISO 13943:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, 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
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CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST EN ISO 13943:2017
ISO 13943:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

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

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

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

Bibliography .............................................................................................................................................................................................................................52

Index of deprecated terms .........................................................................................................................................................................................52

© ISO 2017 – All rights reserved iii
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SIST EN ISO 13943:2017
ISO 13943:2017(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 on 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 the following

URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety.

This third edition cancels and replaces the second edition (ISO 13943:2008), which has been technically

revised.
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SIST EN ISO 13943:2017
ISO 13943:2017(E)
Introduction

Over the last two decades, there has been a significant growth in the field of fire safety. There has been

a considerable development of fire safety engineering design, especially as it relates to construction

projects, as well as the development of concepts related to performance-based design. With this

continuing evolution, there is an increasing need for agreement on a common language in the broad and

expanding area of fire safety, beyond what traditionally has been limited to the field of fire testing.

The first edition of this vocabulary, ISO 13943:2000, contained definitions of about 180 terms. However,

the areas of technology that are related to fire safety have continued to evolve rapidly and this edition

contains many new terms and their definitions, as well as revised definitions of some of the terms that

were in earlier editions.

This document defines general terms to establish a vocabulary applicable to fire safety, including fire

safety in buildings and civil engineering works and other elements within the built environment. It will

be updated as terms and definitions for further concepts in the field of fire safety are agreed upon and

developed.

It is important to note that, it is possible that, when used for regulation, some fire safety terms may have

a somewhat different interpretation than the one used in this document and, in that case, the definition

given in this document may not apply.
The terms in this document are
— fundamental concepts,

— more specific concepts, such as those used specifically in fire testing or in fire safety engineering

and may be used in ISO or IEC fire standards, and

— related concepts, as exemplified by terms used in building and civil engineering.

Annex A provides an index of deprecated terms.

The layout is designed according to ISO 10241-1, unless otherwise specified. The terms are presented in

English alphabetical order and are in bold type except for deprecated terms, which are in normal type.

Use of the term “item”

For the purposes of this document, in the English version, the term “item” (and in French “objet”) is

used in a general meaning to represent any single object or assembly of objects, and may cover, for

example, material, product, assembly, structure or building, as required in the context of any individual

definition.

If the “item” under consideration is a test specimen, then the term “test specimen” is used.

The German version uses terminology such as material, product, kit, assembly and/or building to clarify

the meaning of each definition.
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SIST EN ISO 13943:2017
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SIST EN ISO 13943:2017
INTERNATIONAL STANDARD ISO 13943:2017(E)
Fire safety — Vocabulary
1 Scope

This document defines terminology relating to fire safety as used in ISO and IEC fire standards.

2 Normative references
There are no normative references in this document.
3 Terms and definitions

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

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
abnormal heat

heat that is additional to that resulting from use under normal conditions, up to and

including that which causes a fire (3.114)
3.2
absorptivity

ratio of the absorbed radiant heat flux (3.319) to the incident radiative heat flux (3.321)

Note 1 to entry: The absorptivity is dimensionless.
3.3
acceptance criteria

criteria that form the basis for assessing the acceptability of the safety of a design of a built

environment (3.32)

Note 1 to entry: The criteria can be qualitative, quantitative or a combination of both.

3.4
accuracy

closeness of the agreement between the result of a measurement and the true value of the measurand

[SOURCE: ASTM E176: 2015]
3.5
activation time

time interval from response by a sensing device until the suppression system (3.375), smoke (3.347)

control system, alarm system or other fire safety system is fully operational
3.6
active fire protection

method(s) used to reduce or prevent the spread and effects of fire (3.114), heat or smoke (3.347) by

virtue of detection and/or suppression of the fire and which require a certain amount of motion and/or

response to be activated

EXAMPLE The application of agents (e.g. halon gas or water spray) to the fire or the control of ventilation

and/or smoke.
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ISO 13943:2017(E)

Note 1 to entry: Compare with the terms passive fire protection (3.293) and suppression systems (3.375).

3.7
actual delivered density
ADD

volumetric flow rate of water per unit area that is delivered onto the top horizontal surface of a

simulated burning combustible (3.52) array

Note 1 to entry: ADD is typically determined relative to a specific heat release rate (3.206) of a fire (3.114).

Note 2 to entry: ADD can be measured according to ISO 6182-7.
Note 3 to entry: The typical unit is mm⋅min .
3.8
acute toxicity
toxicity (3.405) that causes rapidly occurring toxic (3.399) effects
Note 1 to entry: Compare with the term toxic potency (3.402).
3.9
aerosol

suspension of droplets (3.84) and/or solid particles in a gas phase which are generated by fire (3.114)

Note 1 to entry: The size of the droplets or particles typically ranges from under 10 nm to over 10 μm.

Note 2 to entry: Compare with the term droplets.
3.10
aerosol particle

individual piece of solid material that is part of the dispersed phase in an aerosol (3.9)

Note 1 to entry: There are two categories of fire aerosol particles: unburned or partially burned particles

containing a high proportion of carbon (i.e. “soot”), and relatively completely combusted, small particle sized

“ashes”. Soot (3.354) particles of small diameter, (i.e. about 1 μm), typically consist of small elementary spheres

of between 10 nm and 50 nm in diameter. Formation of soot particles is dependent on many parameters including

nucleation, agglomeration and surface growth. Oxidation (3.289) of soot particles, i.e. further combustion (3.55),

is also possible.
3.11
afterflame
flame (3.159) that persists after the ignition source (3.219) has been removed
3.12
afterflame time

length of time for which an afterflame (3.11) persists under specified conditions

Note 1 to entry: Compare with the term duration of flaming (3.85).
3.13
afterglow

persistence of glowing combustion (3.197) after both removal of the ignition source (3.219) and the

cessation of any flaming combustion (3.175)
3.14
afterglow time
length of time for which an afterglow (3.13) persists under specified conditions
3.15
agent outlet

orifice of a piping system by means of which an extinguishing fluid can be applied towards the source

of a fire (3.114)
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ISO 13943:2017(E)
3.16
alarm time

time interval between ignition (3.217) of a fire (3.114) and activation of an alarm

Note 1 to entry: The time of ignition may be known, e.g. in the case of a fire model (3.136) or a fire test (3.157), or

it may be assumed, e.g. it may be based upon an estimate working back from the time of detection. The basis on

which the time of ignition is determined is always stated when the alarm time is specified.

3.17
alight, adj.
lit, adj. CA, US
lighted, adj.
undergoing combustion (3.55)
3.18
analyte
substance that is identified or quantified in a specimen during an analysis
3.19
arc resistance

ability of an electrically insulating material to resist the influence of an electric arc,

under specified conditions

Note 1 to entry: The arc resistance is identified by the length of the arc, the absence or presence of a conducting

path, and the burning or damage of the test specimen (3.384).
3.20
area burning rate
DEPRECATED: burning rate
DEPRECATED: rate of burning
area of material burned (3.34) per unit time under specified conditions
2 −1
Note 1 to entry: The typical unit is m ⋅s .
3.21
arson
crime of setting a fire (3.114), usually with intent to cause damage
3.22
ash
ashes
mineral residue resulting from complete combustion (3.59)
3.23
asphyxiant

toxicant (3.404) that causes hypoxia, which can result in central nervous system depression or

cardiovascular effects
Note 1 to entry: Loss of consciousness and ultimately, death may occur.
3.24
auto-ignition
spontaneous ignition
self-ignition
unpiloted ignition
DEPRECATED: spontaneous combustion
ignition (3.217) caused by an internal exothermic reaction

Note 1 to entry: The ignition may be caused either by self-heating (3.341) or, in the case of unpiloted ignition, by

heating from an external source, as long as the external source does not include an open flame

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Note 2 to entry: In North America, “spontaneous ignition” is the preferred term used to designate ignition

caused by self-heating.

Note 3 to entry: Compare with the terms piloted ignition (3.299) and spontaneous ignition temperature (3.363).

3.25
auto-ignition temperature

minimum temperature at which auto-ignition (3.24) is obtained in a fire test (3.157)

Note 1 to entry: The typical unit is °C.
Note 2 to entry: Compare with the term spontaneous ignition temperature (3.363).
3.26
available safe escape time
ASET
time available for escape

calculated time interval between the time of ignition (3.217) and the time at which conditions become

such that the occupant is estimated to be incapacitated, i.e. unable to take effective action to escape

(3.99) to a safe refuge (3.333) or place of safety (3.300)

Note 1 to entry: The time of ignition may be known, e.g. in the case of a fire model (3.136) or a fire test (3.157), or

it may be assumed, e.g. it may be based upon an estimate working back from the time of detection. The basis on

which the time of ignition is determined needs to be stated.

Note 2 to entry: This definition equates incapacitation (3.225) with failure to escape. Other criteria for ASET are

possible. If an alternate criterion is selected, it needs to be stated.

Note 3 to entry: Each occupant may have a different value of ASET, depending on that occupant’s personal

characteristics.
3.27
backdraft

rapid flaming combustion (3.175) caused by the sudden introduction of air into a confined oxygen-

deficient space that contains hot products of incomplete combustion (3.55)

Note 1 to entry: In some cases, these conditions may result in an explosion (3.105).

3.28
behavioural scenario
description of the behaviour of occupants during the course of a fire (3.114)
3.29
black body
form that completely absorbs any electromagnetic radiation falling upon it
3.30
black body radiation source

ideal thermal radiation source which completely absorbs all incident heat radiation, whatever

wavelength and direction
Note 1 to entry: The emissivity (3.89) of a black body radiant source is unity.
Note 2 to entry: A black body can also be an ideal radiator of energy.
[SOURCE: ISO 14934-1:2010, 3.1.7]
3.31
building element
integral part of a built environment (3.32)

Note 1 to entry: This includes floors, walls, beams, columns, doors, and penetrations, but does not include

contents.
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ISO 13943:2017(E)

Note 2 to entry: This definition is wider in its scope than that given in ISO 6707-1.

3.32
built environment
building or other structure

EXAMPLE Off-shore platforms, civil engineering works such as tunnels, bridges and mines, and means of

transportation such as motor vehicles and marine vessels.

Note 1 to entry: ISO 6707-1 contains a number of terms and definitions for concepts related to the built

environment.
3.33
buoyant plume
convective updraft of fluid above a heat source
Note 1 to entry: Compare with the term fire plume (3.138).
3.34
burn, intransitive verb
undergo combustion (3.55)
3.35
burn, transitive verb
cause combustion (3.55)
3.36
burned area

that part of the damaged area (3.72) of a material that has been destroyed by combustion (3.55) or

pyrolysis (3.316), under specified conditions
Note 1 to entry: The typical unit is m .
3.37
burned length
maximum extent in a specified direction of the burned area (3.36)
Note 1 to entry: The typical unit is m.
Note 2 to entry: Compare with the term damaged length (3.73).
3.38
burning behaviour

response of a test specimen (3.384), when it burns under specified conditions, to examination

of reaction to fire (3.324) or fire resistance (3.141)
3.39
burning debris

burning material, other than drops, which has detached from a test specimen (3.384) during a fire test

(3.157) and continues to burn (3.34) on the floor

Note 1 to entry: Compare with the terms burning droplets (3.40), flaming debris (3.176) and flaming droplets

(3.177).
3.40
burning droplets

flaming molten or flaming liquefied drops which fall from a test specimen (3.384) during a fire test

(3.157) and continue to burn (3.34) on the floor

Note 1 to entry: Compare with the terms flaming droplet (3.177), flaming debris (3.176) and burning debris (3.39).

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SIST EN ISO 13943:2017
ISO 13943:2017(E)
3.41
bursting
violent rupture of an object due to an overpressure within it or upon it
3.42
calibration

process of adjusting modelling parameters in a computational fire model (3.136) for the

purpose of improving agreement with experimental data
3.43
calorimeter
apparatus that measures heat

Note 1 to entry: Compare with the terms heat release rate calorimeter (3.207) and mass calorimeter (3.257).

3.44
carboxyhaemoglobin
compound formed when CO combines with haemoglobin

Note 1 to entry: Haemoglobin has an affinity for binding to CO that is approximately 245 times higher than that

for binding to oxygen; thereby, the ability of haemoglobin to carry oxygen is seriously compromised during CO

poisoning.
3.45
carboxyhaemoglobin saturation

percentage of blood haemoglobin converted to carboxyhaemoglobin from the reversible reaction with

inhaled carbon monoxide
3.46
ceiling jet

gas motion in a hot gas layer near a ceiling that is generated by the buoyancy of a fire plume (3.138) that

is impinging upon the ceiling
3.47
char, noun

carbonaceous residue resulting from pyrolysis (3.316) or incomplete combustion (3.55)

3.48
char, verb
form char (3.47)
3.49
char length
length of charred area

Note 1 to entry: Compare with the terms burned length (3.37) and damaged length (3.73).

Note 2 to entry: In some standards, char length is defined by a specific test method.

3.50
chimney effect

upward movement of hot fire effluent (3.123) caused by convection (3.66) currents confined within an

essentially vertical enclosure (3.92)
Note 1 to entry: This usually draws more air into the fire (3.114).
3.51
clinker

solid agglomerate of residues formed by either complete combustion (3.59) or incomplete combustion

(3.55) and which may result from complete or partial melting
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ISO 13943:2017(E)
3.52
combustible, adj.
capable of being ignited (3.216) and burned (3.34)
3.53
combustible, noun
item capable of combustion (3.55)
3.54
combustible load

theoretical mass that would be lost from a test specimen (3.384) when it is assumed to have undergone

complete combustion (3.59) in a fire test (3.157)
3.55
combustion
exothermic reaction of a substance with an oxidizing agent (3.290)

Note 1 to entry: Combustion generally emits fire effluent (3.123) accompanied by flames (3.159) and/or glowing

(3.196).
3.56
combustion efficiency

ratio of the amount of heat release (3.205) in incomplete combustion (3.55) to the theoretical heat of

complete combustion (3.59)

Note 1 to entry: Combustion efficiency can be calculated only for cases where complete combustion can be

defined.
Note 2 to entry: Combustion efficiency is usually expressed as a percentage.
Note 3 to entry: The combustion efficiency is dimensionless.
3.57
combustion product
product of combustion
solid, liquid and gaseous material resulting from combustion (3.55)

Note 1 to entry: Combustion products may include fire effluent (3.123), ash (3.22), char (3.47), clinker (3.51)

and/or soot (3.354).
3.58
common mode failure

failure involving a single source that affects more than one type of safety system simultaneously

3.59
complete combustion
combustion (3.55) in which all the combustion products (3.57) are fully oxidized

Note 1 to entry: This means that, when the oxidizing agent (3.290) is oxygen, all carbon is converted to carbon

dioxide and all hydrogen is converted to water.

Note 2 to entry: If elements other than carbon, hydrogen and oxygen are present in the combustible (3.52)

material, those elements are converted to the most stable products in their standard states at 298 K.

3.60
computerized model
operational computer programme that implements a conceptual model (3.64)
3.61
composite material
structured combination of two or more discrete materials
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ISO 13943:2017(E)
3.62
concentration
mass of a dispersed or dissolved material in a given volume
Note 1 to entry: For fire effluent (3.123), the typical unit is g⋅m .

Note 2 to entry: For toxic gas (3.400), concentration is usually expressed as a volume fraction (3.421) at T = 298 K

3 3 −6
and P = 1 atm, with typical units of μL/L (= cm /m = 10 ).

Note 3 to entry: The concentration of a gas at a temperature, T, and a pressure, P, can be calculated from its

volume fraction (assuming ideal gas behaviour) by multiplying the volume fraction by the density of the gas at

that temperature and pressure.

Note 4 to entry: Pascal (Pa) is the SI unit for pressure; however, atmosphere (atm) is typically used in this context,

where 1 atm = 101,3 kPa.
3.63
concentration-time curve

plot of the concentration (3.62) of a toxic gas (3.400) or fire effluent (3.123) as a

function of time

Note 1 to entry: For fire effluent, concentration is usually measured in units of g⋅m .

Note 2 to entry: For toxic gas, concentration is usually expressed as a volume fraction (3.421) at T = 298 K and

3 3 −6
P = 1 atm, with typical units of μL/L (= cm /m = 10 ).

Note 3 to entry: Pascal (Pa) is the SI unit for pressure; however, atmosphere (atm) is typically used in this context,

where 1 atm = 101,3 kPa.
3.64
conceptual model

information, mathematical modelling, data, assumptions, boundary conditions and mathematical

equations that describes the (physical) system or process of interest
3.65
controlled burn

operational strategy where the application of firefighting media such as water or foam is restricted

or avoided

Note 1 to entry: Controlled burns are often conducted to minimize damage to public health and the environment.

Other motivations for controlled burn may include limited danger of fire spread, concerns about firefighter

safety, or limited capacity and resources at hand for firefighting operations.

Note 2 to entry: The strategy would normally be used to try and prevent water pollution by contaminated

firewater. It can also reduce air pollution due to the better combustion (3.55) and dispersion of pollutants. But it

may also have adverse impacts such as allowing or increasing the formation of hazardous gaseous by-products. It

may also have benefits for fire fighter safety and public health.
3.66
convection
transfer of heat by movement of a fluid
3.67
convective heat flux
heat flux (3.201) caused by convection (3.66)
3.68
convective heat transfer
transfer of heat to a surface from a surrounding fluid by convection (3.66)

Note 1 to entry: The amount of heat transfer depends on the temperature difference between the fluid and the

surface, the fluid properties and the fluid velocity and direction.
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