Smoke and heat control systems — Part 4: Natural smoke and heat exhaust ventilators — Design, requirements and installation

This document applies to the design and installation of natural smoke and heat exhaust ventilators (NSHEVs) for spaces from which smoke is extracted vertically by thermal buoyancy via the roof in the case of single-storey buildings and via the uppermost storey in the case of multi-storey buildings. It also applies to spaces in which NSHEVs are installed in external walls. This document includes tables and calculation methods for the design of clear layers in order to comply with the requirements of various protection objectives. This document includes information and provisions to be taken into account when applying the design rules set out herein and when installing NSHEVs.

Systèmes pour le contrôle des fumées et de la chaleur — Partie 4: Exutoires de fumées et de chaleur naturels — Dimensionnement, exigences et mise en place

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Status
Published
Publication Date
01-Apr-2019
Current Stage
6060 - International Standard published
Due Date
06-Feb-2020
Completion Date
02-Apr-2019
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INTERNATIONAL ISO
STANDARD 21927-4
First edition
2019-04
Smoke and heat control systems —
Part 4:
Natural smoke and heat exhaust
ventilators — Design, requirements
and installation
Systèmes pour le contrôle des fumées et de la chaleur —
Partie 4: Exutoires de fumées et de chaleur naturels —
Dimensionnement, exigences et mise en place
Reference number
ISO 21927-4:2019(E)
©
ISO 2019

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ISO 21927-4:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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ISO 21927-4:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Design principles . 2
5.1 General . 2
5.2 Height of space . 3
5.3 Target height of the clear layer, height of smoke barrier . 3
5.4 Area of smoke reservoir . 4
5.5 Air inlets . 4
5.6 Duration of fire growth . 5
5.7 Theoretical fire area, design groups . 5
5.8 Aerodynamic effectiveness of NSHEVs . 6
6 Design . 6
6.1 General . 6
6.2 Smoke exhaust openings in roofs . 6
6.3 Smoke exhaust openings in walls .12
7 Installation .13
7.1 General .13
7.2 Rules for installation .13
8 NSHEVs combined with fire extinguishing equipment .14
9 Testing, maintenance and repair .15
9.1 Testing .15
9.2 Maintenance .15
9.3 Repair .15
Bibliography .16
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ISO 21927-4:2019(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 21, Equipment for fire protection and fire
fighting, Subcommittee SC 11, Smoke and heat control systems and components.
A list of all parts in the ISO 21927 series can be found on the ISO website.
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.
iv © ISO 2019 – All rights reserved

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ISO 21927-4:2019(E)

Introduction
Smoke and heat control systems (SHCS) create and maintain smoke free areas in a construction works
by controlling smoke flow and thus improve the conditions for the safe escape and/or rescue of people
and animals and the protection of property and permit the fire to be fought while still in its early
stages. The use of smoke and heat exhaust ventilation systems (SHEVS) to create smoke free areas
beneath a buoyant smoke layer has become widespread. Their value in assisting in the evacuation of
people from construction works, reducing fire damage and financial loss by preventing smoke logging,
facilitating firefighting, reducing roof temperatures and retarding the lateral spread of fire is firmly
established. For these benefits to be obtained, it is essential that smoke and heat exhaust ventilators
operate fully and reliably whenever called upon to do so during their installed life. A heat and smoke
exhaust ventilation system is a scheme of safety equipment intended to perform a positive role in a fire
emergency.
Components for any smoke and heat control system are installed as part of a properly designed system.
Smoke and heat control systems help to:
— keep escape and access routes free from smoke;
— facilitate firefighting operations;
— delay and/or prevent flashover and thus full development of a fire;
— protect equipment and furnishings;
— reduce thermal effects on structural components during a fire;
— reduce damage due to thermal decomposition products and hot gases.
Pressure differential systems are used either to positively pressurize spaces separated from the fire or
to depressurize the space containing the fire in order to limit or prevent the flow of smoke and heat into
adjacent spaces. A typical use would be to pressurize an escape stair well in order to protect vertical
means of escape.
Depending on the design of the system, natural or powered smoke and heat ventilators can be used in a
smoke and heat control system.
Control equipment is needed in order to control all components in a SHCS, such as:
— natural ventilators;
— powered ventilators;
— smoke barriers;
— smoke dampers;
— air inlets;
— duct sections;
— dampers.
SHCS control equipment can also provide control for day-to-day ventilation and signals to other fire
safety equipment under fire conditions.
SHCS control equipment can be for extra-low voltage or low voltage electrical systems or pneumatic
systems or any combination thereof.
Power output devices for control equipment are dealt with in ISO 21927-10.
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INTERNATIONAL STANDARD ISO 21927-4:2019(E)
Smoke and heat control systems —
Part 4:
Natural smoke and heat exhaust ventilators — Design,
requirements and installation
1 Scope
This document applies to the design and installation of natural smoke and heat exhaust ventilators
(NSHEVs) for spaces from which smoke is extracted vertically by thermal buoyancy via the roof in the
case of single-storey buildings and via the uppermost storey in the case of multi-storey buildings. It
also applies to spaces in which NSHEVs are installed in external walls.
This document includes tables and calculation methods for the design of clear layers in order to comply
with the requirements of various protection objectives.
This document includes information and provisions to be taken into account when applying the design
rules set out herein and when installing NSHEVs.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
ISO 21927-1, Smoke and heat control systems — Part 1: Specification for smoke barriers
ISO 21927-2, Smoke and heat control systems — Part 2: Specification for natural smoke and heat exhaust
ventilators
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
aerodynamic free area
measure of smoke and heat exhaust area of the ventilator
Note 1 to entry: It is the geometric area multiplied by the coefficient of discharge.
3.2
automatic activation
initiation of operation without direct human intervention
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ISO 21927-4:2019(E)

3.3
coefficient of discharge
aerodynamic efficiency
c
v
ratio of actual flow rate, measured under specified conditions, to the theoretical flow rate through the
ventilator
Note 1 to entry: The coefficient takes into account any obstructions in the ventilator, such as controls, louvres
and vanes, and the effect of external side winds.
3.4
exhaust ventilator
device for the movement of gases out of the construction works
3.5
initiation device
device that activates the operating mechanism of the component, e.g. of a damper or a ventilator, on
receipt of information from a fire detection system or thermal device
3.6
smoke and heat exhaust ventilation system
SHEVS
group of components jointly selected to exhaust smoke and heat in order to establish a buoyant layer of
warm gases above cooler and cleaner air
3.7
natural smoke and heat exhaust ventilator
NSHEV
product specially designed to move smoke and hot gases out of a construction works naturally under
conditions of fire
4 Symbols and abbreviated terms
Symbol Definition Unit
2
A area of smoke exhaust opening m
a
2
A fire area m
fa
2
A area of air inlet m
in
2
A area of smoke reservoir m
R
c factor for determining the area of the air inlet —
z
d height of clear layer m
h height of space to be protected m
H height of smoke barrier m
sb
z height of smoke layer (h – d) m
5 Design principles
5.1 General
The design of natural smoke and heat exhaust ventilation systems (see Figure 1) depends, inter alia, on:
— the rate of energy release;
— the theoretical fire area of a building or the resulting design group;
— the target height of the clear layer; and
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ISO 21927-4:2019(E)

— the height of the relevant space.
Key
2
A area of smoke exhaust opening, in m z height of smoke layer (h – d), in m
a
2
A area of air inlet, in m 1 clear layer
in
d height of clear layer, in m 2 plume
h height of space to be protected, in m 3 smoke layer
H height of smoke barrier, in m
SB
Figure 1 — Diagram of a natural smoke and heat exhaust ventilation system in a smoke
reservoir
The values to be used to determine the parameters above are auxiliary design values and only apply to
designs in accordance with this document.
5.2 Height of space
The height, h, of the space to be protected shall be the clear height in the case of horizontal roofs/
floors and the mean clear height in the case of pitched roofs or sloping floors. In both cases. it shall
be measured from the floor to the lower surface of the roof/floor. Floors with smoke outlets are not
regarded as floors in this context.
In the case of sawtooth roofs, the height of the space to be used for design purposes is the mean height
of the NSHEV above the floor.
5.3 Target height of the clear layer, height of smoke barrier
The clear layer is defined as the distance between the surface of the floor assumed for design purposes
and the lower surface of the smoke layer.
Clear layers enable, inter alia:
— the occupants of a building to escape to safety;
— the emergency services to rescue people, animals and property;
— fires to be fought effectively; and
— damage due to fire gases and products of thermal decomposition to be reduced.
The target height of the clear area, d, shall be not less than 2,50 m.
Design should be based on higher values of d if required by the purpose for which the space is to be
used (e.g. spaces containing objects sensitive to smoke or flammable warehouse stock). The distance
between the objects to be protected and the smoke layer should be not less than 0,5 m.
For clear layers with a height d ≤ 4 m, the height of the smoke barrier shall protrude at least 0,5 m into
the clear layer. For clear layers with a height d > 4 m the smoke barrier shall at least equal to the height
of the smoke layer, z, but not less than 1,0 m in all cases.
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ISO 21927-4:2019(E)

5.4 Area of smoke reservoir
To enable NSHEVs to be designed according to this document, spaces shall either have a maximum area
2 2
of 1 600 m or be divided into smoke reservoirs with a maximum area, A , of 1 600 m by means of
R
smoke barriers. The maximum distance between smoke barriers or between wall and smoke barrier
shall not exceed 60 m. Any further subdivisions (e.g. closed joists) within the smoke reservoir shall not
affect the design.
NOTE Smoke reservoirs are created by placing separating elements around the perimeter of a space or, at
the minimum, by placing continuous smoke barriers around the open inner sides of a space. A “space” is defined
as an area enclosed by separating elements on all sides.
5.5 Air inlets
An adequate number of air inlets, with an area, A , is always required in the lower part of external
in
walls to act as air replacement openings near floor level.
The required area of the air inlets shall be based on the area of the largest smoke reservoir. This area
shall be taken into account when designing the external walls of a space. The air inlets should be located
on at least two sides of the building and should be evenly distributed.
The following are considered as air inlets:
— separate supply air devices;
— doors or windows provided they are labelled as “air inlets for NSHEVs” on the inside and outside and
can be opened from outside without being destroyed in the process (e.g. it shall not be necessary to
smash window panes or break down walls or doors). This does not apply in cases in which a works
fire service is able to create the necessary air inlets.
It shall be possible to open the air inlets immediately (e.g. automatically, by the works fire service or as
a result of operational or organizational measures) after the NSHEVs have been activated.
The effective area of the air inlets shall be not less than 1,5 times the aerodynamic free areas of all
NSHEV openings in the largest smoke reservoir in a space, as specified in Table 3.
The effective area of the following types of air inlet shall be obtained by correcting the area of the
structural opening by a factor, c , as specified in Table 1.
z
Table 1 — Correction factors, c , for different types of opening serving as air inlets
z
Correction factor
Type of opening Opening angle
c
z
Door openings, wire mesh 0,7
Openable shutters 90° 0,65
90° 0,65
≥60° 0,5
Side-hung or bottom-hung windows
≥45° 0,4
≥30° 0,3
A tolerance of ±5° is permitted for the opening angles specified in Table 1.
The factor c used to assess the effective area of an air inlet, as obtained from the area of the wall
z
opening and the opening angle, should not be confused with the c value. The latter is used to obtain the
v
aerodynamic free area of smoke exhaust openings, A , from the geometrical inlet area, A , of smoke and
a g
heat exhaust ventilators.
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ISO 21927-4:2019(E)

The distance between the upper edge of the air inlet and the bottom of the layer of smoke gases shall
be not less than 1 m. The distance may be reduced to 0,50 m in the vicinity of doors or windows with a
width not greater than 1,25 m.
In the case of air inlets resulting in an upward air flow (e.g. those with protective gratings facing
upwards) the distance between the upper edge of the air inlet and the bottom of the layer of smoke
gases should be not less than 1,5 m.
5.6 Duration of fire growth
The duration of fire growth to be assumed for the purposes of this document (see Table 2) is the time
that elapses between the outbreak of a fire and the start of firefighting measures.
The time that elapses between the outbreak of a fire and the alarm being raised shall be taken as 10 min.
This period of time does not apply where fire alarm systems incorporating automatic fire detectors
activated by smoke have been installed. The fire alarm shall be transmitted to a fire station or other
station that can provide assistance and is manned around the clock.
It does not apply either to spaces that are continuously manned, ensuring that any fire is detected
immediately and the fire service notified accordingly.
It shall be taken as 5 min where NSHEVs are fitted with automatic fire detectors activated by smoke.
2
In such cases, it is sufficient to install one smoke detector per every 200 m of the smoke reservoir. A
distance of 10 m between beams is sufficient for linear smoke detectors.
A mean time of 10 min shall be assumed for the time that elapses between the fire alarm being raised
and the start of firefighting measures. In favourable circumstances, such as where there are on-
site firefighters who can reach the scene of a fire in less than 5 min, it may be reduced to 5 min. The
mean time shall be increased to 15 min if the circumstances are unfavourable and to 20 min if the
circumstances are exceptionally unfavourable.
The times referred to in this clause are auxiliary design values and are only to be used when calculating
the fire growth rate needed for the purposes of this standard.
5.7 Theoretical fire area, design groups
The theoretical fire area is obtained from the fire propagation rate and the assumed duration of fire
growth. The design group is based on the theoretical fire area (see Table 2).
Table 2 — Design groups
Assumed duration of fire Design group for specific fire propagation rates
growth
(see 5.6) <0,15 m/min <0,25 m/min <0,45 m/min
a
particularly low average particularly high
min
≤5 1 2 3
≤10 2 3 4
≤15 3 4 5
a a b
≤20 4 5 5
b b
>20 5 5 5
a
Average values without specific verification; design group 5 (in bold) is obtained if the average values are used.
b
In such cases, the protection objectives set out in this standard cannot be achieved solely by means of NSHEVs and
other measures are required in order to achieve them.
The highest fire propagation rate shall always apply if the individual smoke reservoirs within a space
are used in different ways so that very different fire propagation rates can be expected.
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ISO 21927-4:2019(E)

Generally, the values given in the column "average" of Table 2 shall be used. The values given in the
column "particularly low" may be used for particularly low fire propagation rates (e.g. combustible
materials in non-combustible packaging) while those in the column "particularly high" shall be used for
particularly high fire propagation rates (e.g. readily flammable materials in combustible packaging).
In cases in which design group 4 or 5 is obtained from Table 2, design group 3 may be used without
further verification if an automatic sprinkler system covering the entire area has been installed.
5.8 Aerodynamic effectiveness of NSHEVs
The aerodynamic effectiveness of the smoke exhaust openings of NSHEVs installed in roofs shall be
verified in accordance with the methods described in ISO 21927-2. Information on the aerodynamic
effectiveness of smoke exhaust openings of NSHEVs installed in walls is given in 6.3.
6 Design
6.1 General
The area of the smoke exhaust openings to be provided to enable smoke to be removed from each smoke
2
reservoir ("required area of smoke exhaust openings") is specified as a minimum area, in m , in Table 3
as the development of a fire and the resultant smoke does not depend on the size of the smoke reservoir
in which the outbreak occurs.
The area of the smoke exhaust openings specified here shall be provided in each smoke reservoir,
2 2
irrespective of its size (applies to smoke reservoirs with an area between 200 m and 1 600 m ).
6.2 Smoke exhaust openings in roofs
The overall aerodynamic free area of the smoke exhaust openings, A , of NSHEVs required for each
a
smoke reservoir, A , in a space shall be taken from Table 3. Table 3 applies to various design groups and
R
various heights of spaces and clear layers.
2
Table 3 — Required area of the smoke exhaust openings, A , per m in each smoke reservoir
a
Height of Height of Height of clear Required area of the smoke exhaust openings
a 2
space smoke layer layer A in m
a
h z d Design group
m m m 1 2 3 4 5
3,0 0,5 2,5 4,8 6,2 8,2 11,0 15,4
1,0 2,5 3,4 4,4 5,8 7,8 10,9
3,5
0,5 3,0 6,7 8,7 11,3 15,0 20,4
1,5 2,5 2,8 3,6 4,7 6,4 8,9
4,0
1,0 3,0 4,8 6,2 8,0 10,6 14,4
2,0 2,5 2,4 3,1 4,1 5,5 7,7
4,5 1,5 3,0 3,9 5,0 6,5 8,7 11,8
1,0 3,5 5,9 8,4 10,7 13,9 18,6
a
For intermediate values, the next highest value in the table shall be selected.
b
The tabulated values for spaces with a height of 12 m may be used for spaces exceeding 12 m in height if calculations
are based on the height of the relevant clear layer.
NOTE  The values of A given in this table do not include any safety increments.
a
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ISO 21927-4:2019(E)

Table 3 (continued)
Height of Height of Height of clear Required area of the smoke exhaust openings
a 2
space smoke layer layer A in m
a
h z d Design group
m m m 1 2 3 4 5
2,5 2,5 2,2 2,8 3,6 4,9 6,9
2,0 3,0 3,4 4,4 5,7 7,5 10,2
5,0
1,5 3,5 4,8 6,8 8,7 11,4 15,2
1,0 4,0 7,1 10,3 13,8 17,7 23,4
3,0 2,5 2,0 2,5 3,3 4,5 6,3
2,5 3,0 3,0 3,9 5,1 6,7 9,1
5,5 2,0 3,5 4,2 5,9 7,5 9,8 13,1
1,5 4,0 5,8 8,5 11,3 14,5 19,1
1,0 4,5 8,2 12,2 17,4 22,2 28,8
3,5 2,5 1,8 2,3 3,1 4,2 5,8
3,0 3,0 2,7 3,6 4,6 6,1 8,3
2,5 3,5 3,7 5,3 6,7 8,8 11,8
6,0
2,0 4,0 5,0 7,3 9,8 12,6 16,5
1,5 4,5 6,7 10,0 14,2 18,1 23,5
1,0 5,0 9,3 14,0 20,5 27,2 35,0
4,0 2,5 1,7 2,2 2,9 3,9 5,4
3,5 3,0 2,6 3,3 4,3 5,7 7,7
3,0 3,5 3,4 4,8 6,2 8,0 10,7
6,5 2,5 4,0 4,5 6,5 8,7 11,2 14,8
2,0 4,5 5,8 8,6 12,3 15,7 20,4
1,5 5,0 7,6 11,4 16,7 22,2 28,6
1,0 5,5 10,3 15,7 23,4 32,7 41,8
4,5 2,5 1,6 2,1 2,7 3,7 5,1
4,0 3,0 2,4 3,1 4,0 5,3 7,2
3,5 3,5 3,2 4,5 5,7 7,4 9,9
3,0 4,0 4,1 6,0 8,0 10,2 13,5
7,0
2,5 4,5 5,2 7,7 11,0 14,0 18,2
2,0 5,0 6,6 9,9 14,5 19,2 24,7
1,5 5,5 8,4 12,8 19,1 26,7 34,2
1,0 6,0 11,9 17,3 26,3 38,5 49,4
a
For intermediate values, the next highest value in the table shall be selected.
b
The tabulated values for spaces with a height of 12 m may be used for spaces exceeding 12 m in height if calculations
are based on the height of the relevant clear layer.
NOTE  The values of A given in this table do not include any safety increments.
a
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ISO 21927-4:2019(E)

Table 3 (continued)
Height of Height of Height of clear Required area of the smoke exhaust openings
a 2
space smoke layer layer A in m
a
h z d Design group
m m m 1 2 3 4 5
5,0 2,5 1,5 2,0 2,6 3,5 4,9
4,5 3,0 2,2 2,9 3,8 5,0 6,8
4,0 3,5 3,0 4,2 5,3 7,0 9,3
3,5 4,0 3,8 5,5 7,4 9,5 12,5
7,5 3,0 4,5 4,8 7,0 10,0 12,8 16,6
2,5 5,0 5,9 8,8 13,0 17,2 22,1
2,0 5,5 7,3 11,1 16,6 23,2 29,6
1,5 6,0 9,7 14,1 21,4 31,4 40,3
1,0 6,5 14,4 18,7 28,9 43,1 57,7
5,5 2,5 1,5 1,9 2,5 3,3 4,6
5,0 3,0 2,1 2,8 3,6 4,8 6,5
4,5 3,5 2,8 3,9 5,0 6,6 8,8
4,0 4,0 3,6 5,2 6,9 8,9 11,7
3,5 4,5 4,4 6,5 9,3 11,8 15,4
8,0
3,0 5,0 5,4 8,1 11,9 15,7 20,2
2,5 5,5 6,5 9,9 14,8 20,7 26,5
2,0 6,0 8,4 12,2 18,6 27,2 34,9
1,5 6,5 11,7 15,2 23,6 35,2 47,1
1,0 7,0 17,1 19,9 31,4 47,7 66,8
6,0 2,5 1,4 1,8 2,4 3,2 4,4
5,5 3,0 2,0 2,6 3,4 4,5 6,2
5,0 3,5 2,7 3,7 4,8 6,2 8,3
4,5 4,0 3,3 4,9 6,5 8,4 11,0
4,0 4,5 4,1 6,1 8,7 11,1 14,4
8,5 3,5 5,0 5,0 7,5 11,0 14,5 18,7
3,0 5,5 5,9 9,1 13,5 18,9 24,1
2,5 6,0 7,5 10,9 16,6 24,4 31,2
2,0 6,5 10,2 13,2 20,5 30,5 40,8
1,5 7,0 13,9 16,2 25,7 38,9 54,6
1,0 7,5 20,0 22,0 33,7 52,0 76,5
a
For intermediate values, the next highes
...

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