IEC 60695-7-3:2011

IEC 60695-7-3 ®
Edition 1.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ

Fire hazard testing –
Part 7-3: Toxicity of fire effluent – Use and interpretation of test results

Essais relatifs aux risques du feu –
Partie 7-3: Toxicité des effluents du feu – Utilisation et interprétation des
résultats d'essai
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IEC 60695-7-3 ®
Edition 1.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ

Fire hazard testing –
Part 7-3: Toxicity of fire effluent – Use and interpretation of test results

Essais relatifs aux risques du feu –
Partie 7-3: Toxicité des effluents du feu – Utilisation et interprétation des
résultats d'essai
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 13.220.40; 29.020 ISBN 978-2-88912-629-3

– 2 – 60695-7-3 © IEC:2011
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references. 7
3 Terms and definitions . 8
4 Principles of toxic hazard assessment . 14
4.1 General . 14
4.2 Exposure dose. 15
4.3 Determination of concentration-time data . 16
4.4 Asphyxiants and the fractional effective dose, FED . 17
4.4.1 General . 17
4.4.2 Properties of the FED . 17
4.4.3 Uses of the FED . 18
4.5 Irritants and the fractional effective concentration, FEC . 18
4.6 Carbon dioxide . 19
4.7 Oxygen vitiation . 19
4.8 Heat stress . 19
4.9 Effects of stratification and transport of fire atmospheres . 19
5 Methods of toxic hazard assessment . 19
5.1 General approach . 19
5.2 Equations used to predict death . 19
5.2.1 Simple toxic gas model . 19
5.2.2 The N-gas model . 20
5.2.3 Hyperventilatory effect of carbon dioxide . 20
5.2.4 Lethal toxic potency values . 20
5.2.5 Mass loss model . 21
5.3 Equations used to predict incapacity . 21
5.3.1 Asphyxiant gas model . 21
5.3.2 Irritant gas model . 22
5.3.3 Mass loss model . 22
6 Toxic potency values . 22
6.1 Generic values of toxic potency . 22
6.2 Toxic potency values obtained from chemical analyses . 22
6.3 Toxic potency values obtained from animal tests . 22
7 Limitations on the interpretation of toxicity test results . 22
8 Effluent components to be measured . 23
8.1 Minimum reporting . 23
8.2 Additional reporting . 23
8.2.1 Gaseous fire effluent components . 23
8.2.2 Airborne particulates . 24
Annex A (informative) Guidance for the use of LC values . 25
Annex B (informative) A simple worked example to illustrate the principles of a toxic
hazard analysis . 28
Annex C (informative) F values for irritants . 32
Bibliography . 33

60695-7-3 © IEC:2011 – 3 –
Figure 1 – Exposure dose as a function of time and concentration . 15
Figure 2 – Time dependent components of fire hazard . 16
Figure 3 – Total FED and contributors, as a function of time . 18
Figure B.1 – Flame spread rate for materials A and B . 29
Figure B.2 – Relative toxic hazard of two materials – time to lethality, i.e. FED ≥ 1 . 31

Table 1 – Some toxic potency values . 20
Table 2 – Combustion products . 24
Table B.1 – Example FED calculation data for material A . 30
Table B.2– Example FED calculation data for material B . 30
Table C.1 – F values for irritants . 32

– 4 – 60695-7-3 © IEC:2011
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE HAZARD TESTING –
Part 7-3: Toxicity of fire effluent –
Use and interpretation of test results

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60695-7-3 has been prepared by IEC technical committee 89: Fire
hazard testing.
This first edition cancels and replaces the second edition of IEC/TS 60695-7-3 published in
2004. It constitutes a technical revision and now has a status of an International Standard.
It has the status of a basic safety publication in accordance with IEC Guide 104 and ISO/IEC
Guide 51.
This International Standard is to be used in conjunction with IEC 60695-7-1 and
IEC 60695-7-2.
The main changes with respect to the previous edition are listed below:
– change of designation from a Technical Specification to an International Standard;

60695-7-3 © IEC:2011 – 5 –
– the Foreword, Introduction, and Clauses 1, 2 and 3 have been updated;
– expanded in all areas to further clarify the alignment with ISO/TC 92 Fire Safety and in
particular with ISO 13344, ISO 13571, ISO/IEC 13943, ISO 16312-1, ISO 16312-2,
ISO 19701, ISO 19702 and ISO 19706;
The text of this standard is based on the following documents:
FDIS Report on voting
89/1058/FDIS 89/1072/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the 60695 series, under the general title Fire hazard testing, can be
found on the IEC website.
Part 7 consists of the following parts:
Part 7-1: Toxicity of fire effluent – General guidance
Part 7-2: Toxicity of fire effluent – Summary and relevance of test methods
Part 7-3: Toxicity of fire effluent – Use and interpretation of test results
Part 7-50: Toxicity of fire effluent – Estimation of toxic potency – Apparatus and test method
Part 7-51: Toxicity of fire effluent – Estimation of toxic potency – Calculation and
interpretation of test results
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 60695-7-3 © IEC:2011
INTRODUCTION
Electrotechnical products sometimes become involved in fires. However, except for certain
specific cases (e.g. power generating stations, mass transit tunnels, computer suites),
electrotechnical products are not normally present in sufficient quantities to form the major
source of toxic hazard. For example, in domestic dwellings and places of public assembly,
electrotechnical products are usually a very minor source of fire effluent compared with, for
example, furnishings.
It should be noted that the IEC 60695-7 series of publications is subject to the ongoing
evolution of fire safety philosophy within ISO/TC 92.
The guidance in this international standard is consistent with the principles of fire safety
developed by ISO TC 92 SC 3 on toxic hazards in fire, as described in ISO 13344, ISO 13571.
ISO 16312-1, ISO 16312-2, ISO 19701, ISO 19702 and ISO 19706. General guidance for the
fire hazard assessment of electrotechnical products is given in IEC 60695-1-10 and
IEC 60695-1-11.
In 1989, the following views were expressed in ISO/TR 9122-1.
"Small-scale toxic potency tests as we know them today are inappropriate for regulatory
purposes. They cannot provide rank orderings of materials with respect to their propensity to
produce toxic atmospheres in fires. All currently available tests are limited because of their
inability to replicate the dynamics of fire growth which determine the time/concentration profiles
of the effluent in full-scale fires, and the response of electrotechnical products, not just
materials. This is a crucial limitation because the toxic effects of combustion effluent are now
known to depend much more on the rates and conditions of combustion than on the chemical
constitution of the burning materials."
Because of these limitations IEC TC 89 has developed IEC 60695-7-50 and ISO subsequently

developed ISO/TS 19700 [1] . Both these standards use the same apparatus. It is a practical
small-scale apparatus which is used to measure toxic potency and which, by virtue of its ability
to model defined stages of a fire, yields toxic potency data suitable for use, with appropriate
additional data, in a full hazard assessment. Both methods use variations in air flow and
temperature to give different physical fire models, but the ISO test method additionally uses the
equivalence ratio as a key parameter.
The evidence from fires and fire casualties, when taken with data from experimental fire and
combustion toxicity studies, suggests that chemical species with unusually high toxicity are not
important (see Clause 7). Carbon monoxide is by far the most significant agent contributing to
toxic hazard. Other agents of major significance are hydrogen cyanide, carbon dioxide and
irritants. There are also other important, non-toxic, threats to life such as the effects of heat,
radiant energy, depletion of oxygen and smoke obscuration, all of which are discussed in
ISO 13571. General guidance on smoke obscuration is provided in IEC 60695-6-1.
IEC TC89 recognizes that effective mitigation of toxic hazard from electrotechnical products is
best accomplished by tests and regulations leading to improved resistance to ignition and to
reduced rates of fire growth, thus limiting the level of exposure to fire effluent and facilitating
escape.
___________
Figures in square brackets refer to the bibliography.

60695-7-3 © IEC:2011 – 7 –
FIRE HAZARD TESTING –
Part 7-3: Toxicity of fire effluent –
Use and interpretation of test results

1 Scope
This part of IEC 60695 concerns laboratory tests used to measure the toxic components of the
fire effluent from either electrotechnical products or materials used in electrotechnical
products. It provides guidance on the use and interpretation of results from such tests. It
discusses currently available approaches to toxic hazard assessment consistent with the
approach of ISO TC 92 SC 3, as set out in ISO 13344, ISO 13571, ISO 16312-1, ISO 16312-2,
ISO 19701, ISO 19702 and ISO 19706. It also provides guidance on the use of toxic potency
data in fire hazard assessment and on principles which underlie the use of combustibility and
toxicological information in fire hazard assessment.
The methods described are applicable to data concerning both the incapacitating effects and
the lethal effects of fire effluents.
This basic safety publication is intended for use by technical committees in the preparation of
standards in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications in the preparation of its publications. The requirements, test methods
or test conditions of this basic safety publication will not apply unless specifically referred to or
included in the relevant publications.
2 Normative references
The following referenced documents are indispensable for the application 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.
IEC 60695-1-10, Fire hazard testing – Part 1-10: Guidance for assessing fire hazard of
electrotechnical products – General guidelines
IEC 60695-1-11, Fire hazard testing – Part 1-11: Guidance for assessing the fire hazard of
electrotechnical products – Fire hazard assessment
IEC 60695-7-1, Fire hazard testing – Part 7-1: Toxicity of fire effluent – General guidance
IEC 60695-7-2, Fire hazard testing – Part 7-2: Toxicity of fire effluent – Summary and
relevance of test methods
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
ISO/IEC Guide 51, Safety aspects – Guidelines for their inclusion in standards
ISO/IEC 13943:2008, Fire safety – Vocabulary
ISO 13344:2004, Estimation of the lethal toxic potency of fire effluents

– 8 – 60695-7-3 © IEC:2011
ISO 13571:2007, Life-threatening components of fire – Guidelines for the estimation of time
available for escape using fire data
ISO 16312-1, Guidance for assessing the validity of physical fire models for obtaining fire
effluent toxicity data for fire hazard and risk assessment – Part 1: Criteria
ISO/TR 16312-2, Guidance for assessing the validity of physical fire models for obtaining fire
effluent toxicity data for fire hazard and risk assessment – Part 2: Evaluation of individual
physical fire models
ISO 19701, Methods for sampling and analysis of fire effluents
ISO 19702, Toxicity testing of fire effluents – Guidance for analysis of gases and vapours in
fire effluents using FTIR gas analysis
ISO 19706 , Guidelines for assessing the fire threat to people
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 13943, some of
which are reproduced below for the user’s convenience, apply.
3.1
asphyxiant
toxicant that causes hypoxia, which can result in central nervous system depression or
cardiovascular effects
NOTE Loss of consciousness and ultimately death can occur.
[ISO/IEC 13943:2008, definition 4.17]
3.2
burn, intransitive verb
undergo combustion
[ISO/IEC 13943:2008, definition 4.28]
3.3
burn, transitive verb
cause combustion
[ISO/IEC 13943:2008, definition 4.29]
3.4
combustible, adjective
capable of being ignited and burned
[ISO/IEC 13943:2008, definition 4.43]
3.5
combustible, noun
item capable of combustion
[ISO/IEC 13943:2008, definition 4.44]
___________
ISO 9122-1: Toxicity testing of fire effluents – Part 1: General has been withdrawn and replaced by ISO 19706.

60695-7-3 © IEC:2011 – 9 –
3.6
combustion
exothermic reaction of a substance with an oxidizing agent
NOTE Combustion generally emits fire effluent accompanied by flames and/or glowing.
[ISO/IEC 13943:2008, definition 4.46]
3.7
concentration
mass per unit volume
–3
NOTE 1 For a fire effluent, the typical units are grams per cubic metre (g × m ).
NOTE 2 For a toxic gas, concentration is usually expressed as a volume fraction at T = 298 K and P = 1 atm, with
3 3 –6
typical units of microlitres per litre (µL/L), which is equivalent to cm /m or 10 .
NOTE 3 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.
[ISO/IEC 13943:2008, definition 4.52]
3.8
effective concentration 50
EC
concentration of a toxic gas or fire effluent, statistically calculated from concentration-response
data, that causes a specified effect in 50 % of a population of a given species within a
specified exposure time and post-exposure time
–3
NOTE 1 For fire effluent, typical units are grams per cubic metre (g × m ).
NOTE 2 For a toxic gas, typical units are microlitres per litre (µL/L) (at T = 298 K and P = 1 atm); see volume
fraction.
NOTE 3 The observed effect is usually a behavioural response, incapacitation, or death. The EC for
incapacitation is termed the IC . The EC for lethality is termed the LC .
50 50 50
[ISO/IEC 13943:2008, definition 4.72]
3.9
effective exposure dose 50
ECt
product of EC and the exposure time over which it was determined
–3
NOTE 1 For fire effluent, typical units are grams times minutes per cubic metre (g × min × m ).
–1
NOTE 2 For a toxic gas, typical units are microlitres times minutes per litre (µL × min × L ) (at T = 298 K and
P = 1 atm); see volume fraction.
NOTE 3 ECt is a measure of toxic potency
[ISO/IEC 13943:2008, definition 4.73]
3.10
equivalence ratio
fuel/air ratio divided by the fuel/air ratio required for a stoichiometric mixture
NOTE 1 Standard, dry air contains 20,95 % oxygen by volume. In practice, the oxygen concentration in entrained
air may vary and calculation of the equivalence ratio to a standard, dry air basis is required.
NOTE 2 The equivalence ratio is dimensionless.
[ISO/IEC 13943:2008, definition 4.81]

– 10 – 60695-7-3 © IEC:2011
3.11
exposure dose
measure of the maximum amount of a toxic gas or fire effluent that is available for inhalation,
calculated by integration of the area under a concentration-time curve
–3
NOTE 1 For fire effluent, typical units are grams times minutes per cubic metre (g × min × m ).
–1
NOTE 2 For a toxic gas, typical units are microlitres times minutes per litre (µL × min × L ) (at T = 298 K and
P = 1 atm); see volume fraction.
[ISO/IEC 13943:2008, definition 4.89]
3.12
fire
(general) process of combustion characterized by the emission of heat and fire effluent and
usually accompanied by smoke, flame, glowing or a combination thereof
NOTE In the English language, the term “fire” is used to designate three concepts, two of which, fire (3.13) and
fire (3.14), relate to specific types of self-supporting combustion with different meanings and two of them are
designated using two different terms in both French and German.
[ISO/IEC 13943:2008, definition 4.96]
3.13
fire
(controlled) self-supporting combustion that has been deliberately arranged to provide useful
effects and is limited in its extent in time and space
[ISO/IEC 13943:2008, definition 4.97]
3.14
fire
(uncontrolled) self-supporting combustion that has not been deliberately arranged to provide
useful effects and is not limited in its extent in time and space
[ISO/IEC 13943:2008, definition 4.98]
3.15
fire effluent
totality of gases and aerosols, including suspended particles, created by combustion or
pyrolysis in a fire
[ISO/IEC 13943:2008, definition 4.105]
3.16
fire hazard
physical object or condition with a potential for an undesirable consequence from fire
[ISO/IEC 13943:2008, definition 4.112]
3.17
fire model
fire simulation
calculation method that describes a system or process related to fire development, including
fire dynamics and the effects of fire
[ISO/IEC 13943:2008, definition 4.116]
3.18
fire scenario
qualitative description of the course of a fire with respect to time, identifying key events that
characterise the studied fire and differentiate it from other possible fires

60695-7-3 © IEC:2011 – 11 –
NOTE It typically defines the ignition and fire growth processes, the fully developed fire stage, the fire decay
stage, and the environment and systems that impact on the course of the fire.
[ISO/IEC 13943:2008, definition 4.129]
3.19
flame spread
propagation of a flame front
[ISO/IEC 13943:2008, definition 4.142]
3.20
flashover
〈stage of fire〉 transition to a state of total surface involvement in a fire of combustible materials
within an enclosure
[ISO/IEC 13943:2008, definition 4.156]
3.21
fractional effective concentration
FEC
ratio of the concentration of an irritant to that concentration expected to produce a specified
effect on an exposed subject of average susceptibility
NOTE 1 As a concept, FEC may refer to any effect, including incapacitation, lethality or other endpoints.
NOTE 2 When not used with reference to a specific irritant, the term “FEC” represents the summation of FEC
values for all irritants in a fire-generated atmosphere.
NOTE 3 The FEC is dimensionless.
[ISO/IEC 13943:2008, definition 4.159]
3.22
fractional effective dose
FED
ratio of the exposure dose for an asphyxiant to that exposure dose of the asphyxiant expected
to produce a specified effect on an exposed subject of average susceptibility
NOTE 1 As a concept, fractional effective dose may refer to any effect, including incapacitation, lethality or other
endpoints.
NOTE 2 When not used with reference to a specific asphyxiant, the term “FED” represents the summation of FED
values for all asphyxiants in a combustion atmosphere.
NOTE 3 The FED is dimensionless.
[ISO/IEC 13943:2008, definition 4.160]
3.23
fully developed fire
state of total involvement of combustible materials in a fire
[ISO/IEC 13943:2008, definition 4.164]
3.24
hyperventilation
rate and/or depth of breathing which is greater than normal
[ISO/IEC 13943:2008, definition 4.180]
3.25
ignition
sustained ignition (deprecated)
〈general〉 initiation of combustion

– 12 – 60695-7-3 © IEC:2011
[ISO/IEC 13943:2008, definition 4.187]
3.26
incapacitation
state of physical inability to accomplish a specific task
NOTE An example of a specific task is to accomplish escape from a fire.
[ISO/IEC 13943:2008, definition 4.194]
3.27
noun
irritant,
〈sensory/upper respiratory〉 gas or aerosol that stimulates nerve receptors in the eyes, nose,
mouth, throat and respiratory tract, causing varying degrees of discomfort and pain with the
initiation of numerous physiological defence responses
NOTE Physiological defence responses include reflex eye closure, tear production, coughing, and
bronchoconstriction.
[ISO/IEC 13943:2008, definition 4.203]
3.28
lethal concentration 50
LC
concentration of a toxic gas or fire effluent, statistically calculated from concentration-response
data, that causes death of 50 % of a population of a given species within a specified exposure
time and post-exposure time
–3
NOTE 1 For fire effluent, typical units are g × m .
NOTE 2 For a toxic gas, the typical units are microlitres per litre (µL/L) (T = 298 K and P = 1 atm); see volume
fraction.
[ISO/IEC 13943:2008, definition 4.207]
3.29
lethal exposure dose 50
LCt
product of LC and the exposure time over which it is determined
NOTE 1 LCt is a measure of lethal toxic potency.
–3
NOTE 2 For fire effluent, the typical units are grams times minutes per cubic metre (g × min × m ).
–1
NOTE 3 For a toxic gas, typical units are microlitres times minutes per litre (µL × min × L ) at T = 298 K and
P = 1 atm; see volume fraction.
[ISO/IEC 13943:2008, definition 4.208]
3.30
mass loss concentration
〈closed system〉 mass of the test specimen consumed during combustion divided by the test
chamber volume
–3
NOTE The typical units are grams per cubic metre (g × m ).
[ISO/IEC 13943:2008, definition 4.222]
3.31
mass loss concentration
〈open system〉 mass of the test specimen consumed during combustion divided by the total
volume of air passed through the test apparatus
NOTE 1 The definition assumes that the mass is dispersed in the air flow uniformly over time.

60695-7-3 © IEC:2011 – 13 –
–3
NOTE 2 The typical units are grams per cubic metre (g × m ).
[ISO/IEC 13943:2008, definition 4.223]
3.32
physical fire model
laboratory process, including the apparatus, the environment and the fire test procedure
intended to represent a certain phase of a fire
[ISO/IEC 13943:2008, definition 4.251]
3.33
pyrolysis
chemical decomposition of a substance by the action of heat
NOTE 1 Pyrolysis is often used to refer to a stage of fire before flaming combustion has begun.
NOTE 2 In fire science no assumption is made about the presence or absence of oxygen.
[ISO/IEC 13943:2008, definition 4.266]
3.34
small-scale fire test
fire test performed on a test specimen of small dimensions
NOTE A fire test performed on a test specimen of which the maximum dimension is less than 1 m is usually called
a small-scale fire test.
[ISO/IEC 13943:2008, definition 4.292]
3.35
smoke
visible part of fire effluent
[ISO/IEC 13943:2008, definition 4.293]
3.36
toxic
poisonous
NOTE A poisonous substance produces adverse effects upon a living organism, e.g. irritation, narcosis or death.
[ISO/IEC 13943:2008, definition 4.335]
3.37
toxic gas
toxic vapour
NOTE In the context of fire effluent, the term is usually applied to a single chemical element or compound.
[ISO/IEC 13943:2008, definition 4.336]
3.38
toxic hazard
potential for harm resulting from exposure to toxic combustion products
[ISO/IEC 13943:2008, definition 4.337]
3.39
toxic potency
measure of the amount of toxicant required to elicit a specific toxic effect
NOTE A small value of toxic potency corresponds to a high toxicity, and vice versa.
[ISO/IEC 13943:2008, definition 4.338]

– 14 – 60695-7-3 © IEC:2011
3.40
toxicant
toxin
toxic substance
[ISO/IEC 13943:2008, definition 4.340]
3.41
toxicity
toxic quality
[ISO/IEC 13943:2008, definition 4.341]
3.42
volume fraction
〈gas in a gas mixture〉 ratio of
− the volume that the gas alone would occupy at a defined temperature and pressure, to:
− the volume occupied by the gas mixture at the same temperature and pressure
NOTE 1 The concentration of a gas at a temperature, T, and at 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 2 Unless stated otherwise, a temperature of 298 K and a pressure of 1 atm are assumed.
NOTE 3 The volume fraction is dimensionless and is usually expressed in terms of microlitres per litre (µL/L),
3 3 –6
which is equivalent to cm /m or 10 ), or as a percentage.
[ISO/IEC 13943:2008, definition 4.351]
3.43
yield
mass of a combustion product generated during combustion divided by the mass loss of the
test specimen
NOTE The yield is dimensionless.
[ISO/IEC 13943:2008, definition 4.354]
4 Principles of toxic hazard assessment
4.1 General
Fire hazard assessment is the discipline of predicting the expected degree of human harm or
property loss resulting from the action of a fire. Toxic hazard assessment is the branch of fire
hazard assessment which addresses the effect of inhaled fire effluent on those exposed.
General guidance on the fire hazard of electrotechnical products is given in IEC 60695-1-10,
and a comprehensive description of the technical background for fire hazard assessment is
presented in IEC 60695-1-11. ISO 13571 address the consequences of human exposure to the
life threat components of fire as occupants move through an enclosed structure, and it includes
the effects of toxic fire effluent.
Toxic hazard assessment attempts to quantify the potential for harm resulting from exposure to
the toxic products of combustion. Until recently, studies have tended to be based on
calculations of exposure times that cause death. However, the emphasis is moving to the
calculation of exposure times that cause incapacitation and which render the victim unable to
escape from the effects of the fire.
Some toxic species act as asphyxiants, e.g. carbon monoxide and hydrogen cyanide. and
others act as irritants, e.g. acrolein, hydrogen chloride and sulphur dioxide. These two types of
toxicants are treated differently. The effects of an asphyxiant depend upon the accumulated

60695-7-3 © IEC:2011 – 15 –
dose, known as the exposure dose, whereas the effects of an irritant depend on whether a
threshold concentration has been reached.
4.2 Exposure dose
For most asphyxiant components of fire effluent, it is commonly assumed that the severity of
the toxic effect is roughly proportional to both the concentration and the time of exposure. This
is known as Haber’s rule. Thus, if the concentration of asphyxiant is doubled and the exposure
time is halved, the toxic effect on an exposed organism is usually about the same [2]. For
some fire effluent components, the toxic response may be more complex. For more
information, the user is referred to ISO 13344 and ISO 13571.
This behaviour is reflected in the use of a parameter known as the exposure dose which is
related to the amount of toxicant available for inhalation from the fire effluent. It is calculated
by integration of the concentration, C, with respect to time, t (see also Figure 1).
Exposure dose = C × dt ( 1 )
∫
If the concentration is constant the exposure dose is simply the product of the concentration
and the exposure time, Ct, but this is not normally the case because in fires the concentrations
of toxicants vary with time.
NOTE Toxicologists sometimes use the symbol Ct for exposure dose even though it is normally calculated by
integration.
Exposure dose
at time  t
Exposure time
IEC  1815/11
Time  t
Figure 1 – Exposure dose as a function of time and concentration
The units of exposure dose are concentration multiplied by time, usually expressed as grams
–3
per cubic metre times minutes (g × min × m ). Sometimes volume fraction (see 3.42) is used
instead of concentration and exposure doses are then usually quoted in units of
–6
10 × min.
NOTE The use of volume fractions makes an assumption that the gas mixture is at a temperature of 25 °C and at
a pressure of 0,1 Mpa. The concentration of the toxicant can be calculated by multiplying the volume fraction by the
density of the pure toxicant at 25 °C and 0,1 Mpa.
Each contributor to the fire effluent will have its own concentration-time curve, and in many
studies all the significant toxic species are considered independently and then their effects are
summed. This approach is known as the “toxic gas model”.
An alternative approach is to consider the fire effluent from a given material or product as a
single toxicant (if its toxic potency is known or can be assumed). In this case the exposure
dose is a function of the exposure time and a parameter known as the mass loss
Concentration
– 16 – 60695-7-3 © IEC:2011
concentration. The different materials or products are considered independently and then their
effects are summed. This approach is known as the “mass loss model”.
4.3 Determination of concentration-time data
There are two ways to determine concentration-time data:
a) by direct measurement in a full-scale simulation of the fire scenario; or
b) by computation of the mass loss rate of the fuels in a model fire scenario.
The computational method can take two forms. For simple situations involving one or two
burning items, hand calculations are often adequate. One such example is presented in
Annex B. In other cases, the approach is often to make use of computer-based mathematical
models. These fire models have so far been developed for simple environments and usually
require as input not only the characteristics of the fire scenario, but also the time-based mass
loss rate of all combustible products exposed to the fire, including electrotechnical products.
Net mass loss for a given product begins when its previously determined ignition conditions
(radiant flux or temperature) are reached. The mass loss rate is proportional to the exposed
surface area and the amount of heat reaching the surface from the fire. The proportionality
constant is determined for each product by laboratory measurements of the mass loss rate per
unit of exposed surface area at a series of known radiant fluxes. Mass loss ceases when the
all the fuel has been calculated to be consumed.
Using mass loss rates and scenario specific information as input, computer codes take into
account the effects of the structure, ventilation and victim location, and calculate effluent
temperature and concentrations at successive times at the selected location. Time dependent
behaviour of various aspects of fire hazard can be obtained as output as illustrated in Figure 2

Temperature
Carbon monoxide
Smoke density
Total toxic gases
% Oxygen
Fuel Mass
Time
Initiation    Detection   Loss of        Incapacity                    Death
effective
visibility
IEC  1816/11
Figure 2 – Time dependent components of fire hazard
Components of fire hazard
(arbitrary scale)
60695-7-3 © IEC:2011 – 17 –
4.4 Asphyxiants and the fractional effective dose, FED
4.4.1 General
The toxic potency of an asphyxiant component is characterized by the size of the exposure
dose required to produce an observed toxic effect. The exposure dose of the toxicant required
to produce a defined effect in 50 % of an exposed population is called
...