IEC 60695-8-1:2016

IEC 60695-8-1 ®
Edition 3.0 2016-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Fire hazard testing –
Part 8-1: Heat release – General guidance

Essais relatifs aux risques du feu –
Partie 8-1: Dégagement de chaleur – Guide général

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IEC 60695-8-1 ®
Edition 3.0 2016-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ

Fire hazard testing –
Part 8-1: Heat release – General guidance

Essais relatifs aux risques du feu –

Partie 8-1: Dégagement de chaleur – Guide général

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.220.40; 29.020 ISBN 978-2-8322-3749-6

– 2 – IEC 60695-8-1:2016  IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Principles of determining heat release . 11
4.1 Complete combustion measured by the oxygen bomb calorimeter . 11
4.2 Incomplete combustion . 12
4.2.1 Measurement techniques . 12
4.2.2 Heat release by oxygen consumption . 12
4.2.3 Heat release by carbon dioxide generation . 13
4.2.4 Heat release by increase of gas temperature . 13
5 Parameters used to report heat release data . 15
5.1 Heat of combustion (gross and net) . 15
5.2 Heat release rate (HRR) . 15
5.3 Heat release (HR) . 16
5.4 Heat release rate per unit area (HRR*) . 16
5.5 Total heat release . 17
5.6 Peak heat release rate . 17
5.7 Time to peak heat release rate . 17
5.8 Effective heat of combustion . 17
5.8.1 Measurement and calculation . 17
5.8.2 Examples. 18
5.9 FIGRA index . 19
5.10 ARHE and MARHE . 20
6 Considerations for the selection of test methods . 22
6.1 Ignition sources . 22
6.2 Type of test specimen . 22
6.3 Choice of conditions . 22
6.4 Test apparatus . 22
6.4.1 General . 22
6.4.2 Small-scale fire test apparatus . 22
6.4.3 Intermediate and large-scale fire test apparatus . 23
6.4.4 Comparison between small-scale and intermediate/large-scale fire test
methods . 23
6.5 Choice of fire tests . 23
7 Relevance of heat release data . 23
7.1 Contribution to fire hazard . 23
7.2 Secondary ignition and flame spread . 23
7.3 Determination of self-propagating fire thresholds . 24
7.4 Probability of reaching flash-over . 24
7.5 Smoke and toxic gas production . 24
7.6 The role of heat release testing in research and development . 24
Bibliography . 25

Figure 1 – Heat release rate (HRR) curve . 16
Figure 2 – Heat release (HR) curve . 16
Figure 3 – Heat release rate per unit area (HRR*) curve . 17
Figure 4 – Mass loss curve . 18
Figure 5 – FIGRA curve derived from Figure 1 . 19
Figure 6 – Illustrative HRR curve . 20
Figure 7 – FIGRA curve derived from Figure 6 . 20
Figure 8 – ARHE curve derived from Figure 1 . 21
Figure 9 – ARHE curve derived from Figure 6 . 21

−1
Table 1 – Relationship between heat of combustion expressed in units of kJ·g of
−1
fuel burned and kJ·g of oxygen consumed for a variety of fuels . 14
−1
Table 2 – Relationship between heat of combustion expressed in units of kJ·g of
−1
fuel burned and kJ·g of oxygen consumed for a variety of insulating liquids . 15

– 4 – IEC 60695-8-1:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE HAZARD TESTING –
Part 8-1: Heat release – General guidance

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
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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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 60695-8-1 has been prepared by IEC technical committee 89: Fire
hazard testing.
This third edition cancels and replaces the second edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) a modified Introduction;
b) reference to IEC 60695-1-12;
c) updated normative references;
d) revised terms and definitions;
e) new text in 4.2.2, 4.2.3, 6.1 and 6.4, including several mandatory statements;
f) mandatory statements in a new Subclause 6.5.

The text of this standard is based on the following documents:
FDIS Report on voting
89/1342/FDIS 89/1348/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.
It has the status of a basic safety publication in accordance with IEC Guide 104 and
ISO/IEC Guide 51.
This standard is to be used in conjunction with IEC 60695-8-2.
A list of all the parts in the IEC 60695 series, under the general title Fire hazard testing, can
be found on the IEC website.
IEC 60695-8 consists of the following parts:
Part 8-1: Heat release – General guidance
Part 8-2: Heat release – Summary of test methods
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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 – IEC 60695-8-1:2016  IEC 2016
INTRODUCTION
In the design of any electrotechnical product, the risk of fire and the potential hazards
associated with fire need to be considered. In this respect the objective of component, circuit
and equipment design as well as the choice of materials is to reduce the risk of fire to a
tolerable level even in the event of reasonably foreseeable (mis)use, malfunction or failure.
IEC 60695-1-10 [1] provides guidance on how this is to be accomplished.
Fires involving electrotechnical products can be initiated from external non-electrical sources.
Considerations of this nature are dealt with in an overall risk assessment.
The aim of the IEC 60695 series of standards is to save lives and property by reducing the
number of fires or reducing the consequences of the fire. This can be accomplished by:
• trying to prevent ignition caused by an electrically energised component part and, in the
event of ignition, to confine any resulting fire within the bounds of the enclosure of the
electrotechnical product;
• trying to minimise flame spread beyond the product’s enclosure and to minimise the
harmful effects of fire effluents including heat, smoke, and toxic or corrosive combustion
products.
Fires are responsible for creating hazards to life and property as a result of the generation of
heat (thermal hazard), toxic and/or corrosive compounds and obscuration of vision due to
smoke. Fire risk increases as the heat released increases, possibly leading to a flash-over fire.
One of the most important measurements in fire testing is the measurement of heat release,
and it is used as an important factor in the determination of fire hazard; it is also used as one
of the parameters in fire safety engineering calculations.
The measurement and use of heat release data, together with other fire test data, can be
used to reduce the likelihood of (or the effects of) fire, even in the event of reasonably
foreseeable (mis)use, malfunction or failure of electrotechnical products.
When a material is heated by some external source, fire effluent can be generated and can
form a mixture with air, which can ignite and initiate a fire. The heat released in the process is
carried away by the fire effluent-air mixture, radiatively lost or transferred back to the solid
material, to generate further pyrolysis products, thus continuing the process.
Heat may also be transferred to other nearby products, which may burn, and then release
additional heat and fire effluent.
The rate at which thermal energy is released in a fire is defined as the heat release rate. Heat
release rate is important because of its influence on flame spread and on the initiation of
secondary fires. Other characteristics are also important, such as ignitability, flame spread
and the side-effects of the fire (see the IEC 60695 series of standards).
______________
Numbers in square brackets refer to the Bibliography.

FIRE HAZARD TESTING –
Part 8-1: Heat release – General guidance

1 Scope
This part of IEC 60695-8 provides guidance on the measurement and interpretation of heat
release from electrotechnical products and materials from which they are constructed.
Heat release data can be used as part of fire hazard assessment and in fire safety

engineering, as described in IEC 60695-1-11 [2] and IEC 60695-1-12 [3].
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 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.
IEC 60695-4:2012, Fire hazard testing – Part 4: Terminology concerning fire tests for
electrotechnical products
IEC 60695-8-2, Fire hazard testing – Part 8-2: Heat release – 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 13943:2008, Fire safety – Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943:2008 and
IEC 60695-4:2012 (some of which are reproduced below), as well as the following, apply.
3.1
combustion
exothermic reaction of a substance with an oxidizing agent
Note 1 to entry: Combustion generally emits fire effluent accompanied by flames and/or glowing.

– 8 – IEC 60695-8-1:2016  IEC 2016
[SOURCE: ISO 13943: 2008, 4.46]
3.2
combustion product
product of combustion
solid, liquid and gaseous material resulting from combustion
Note 1 to entry: Combustion products can include fire effluent, ash, char, clinker and/or soot.
[SOURCE: ISO 13943:2008, 4.48]
3.3
complete combustion
combustion in which all the combustion products are fully oxidized
Note 1 to entry: This means that, when the oxidizing agent 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 material,
those elements are converted to the most stable products in their standard states at 298 K.
[SOURCE: ISO 13943:2008, 4.50]
3.4
effective heat of combustion
heat released from a burning test specimen in a given time interval divided by the mass lost
from the test specimen in the same time period
Note 1 to entry: The value is the same as the net heat of combustion if the entire test specimen is converted to
volatile combustion products and if all the combustion products are fully oxidized.
−1
Note 2 to entry: The typical units are kilojoules per gram (kJ·g ).
[SOURCE: ISO 13943:2008, 4.74]
3.5
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 1 to entry: In the English language the term “fire” is used to designate three concepts, two of which, fire (3.6)
and fire (3.7), 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.
[SOURCE: ISO 13943:2008, 4.96]
3.6
fire
〈controlled〉 self-supporting combustion that has been deliberately arranged to provide useful
effects and is limited in its extent in time and space
[SOURCE: ISO 13943:2008, 4.97]
3.7
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
[SOURCE: ISO 13943:2008, 4.98]

3.8
fire effluent
totality of gases and aerosols, including suspended particles, created by combustion or
pyrolysis in a fire
[SOURCE: ISO 13943:2008, 4.105]
3.9
fire hazard
physical object or condition with a potential for an undesirable consequence from fire
[SOURCE: ISO 13943:2008, 4.112]
3.10
fire safety engineering
application of engineering methods based on scientific principles to the development or
assessment of designs in the built environment through the analysis of specific fire scenarios
or through the quantification of risk for a group of fire scenarios
[SOURCE: ISO 13943:2008, 4.112]
3.11
fire test
test that measures behaviour of a fire or exposes an item to the effects of a fire
Note 1 to entry: The results of a fire test can be used to quantify fire severity or determine the fire resistance or
reaction to fire of the test specimen.
[SOURCE: ISO 13943:2008, 4.132]
3.12
flashover
〈stage of fire〉 transition to a state of total surface involvement in a fire of combustible materials
within an enclosure
[SOURCE: ISO 13943: 2008, 4.156]
3.13
gross heat of combustion
heat of combustion of a substance when the combustion is complete and any produced water
is entirely condensed under specified conditions
cf. complete combustion (3.3)
−1
Note 1 to entry: The typical units are kilojoules per gram (kJ·g ).
[SOURCE: ISO 13943: 2008, 4.170]
3.14
heat of combustion
DEPRECATED: calorific potential
DEPRECATED: calorific value
thermal energy produced by combustion of unit mass of a given substance
cf. effective heat of combustion (3.4), gross heat of combustion (3.13) and net heat of
combustion (3.19)
−1
Note 1 to entry: The typical units are kilojoules per gram (kJ·g ).
[SOURCE: ISO 13943: 2008, 4.174]

– 10 – IEC 60695-8-1:2016  IEC 2016
3.15
heat release
thermal energy produced by combustion
Note 1 to entry: The typical units are joules (J).
[SOURCE: ISO 13943: 2008, 4.176]
3.16
heat release rate
DEPRECATED: burning rate
DEPRECATED: rate of burning
rate of thermal energy production generated by combustion
Note 1 to entry: The typical units are watts (W).
[SOURCE: ISO 13943: 2008, 4.177]
3.17
intermediate-scale fire test
fire test performed on a test specimen of medium dimensions
Note 1 to entry: A fire test performed on a test specimen for which the maximum dimension is between 1 m and
3 m is usually called an intermediate-scale fire test.
[SOURCE: ISO 13943: 2008, 4.200]
3.18
large-scale fire test
fire test, that cannot be carried out in a typical laboratory chamber, performed on a test
specimen of large dimensions
Note 1 to entry: A fire test performed on a test specimen for which the maximum dimension is greater than 3 m is
usually called a large-scale fire test.
[SOURCE: ISO 13943: 2008, 4.205]
3.19
net heat of combustion
heat of combustion when any water produced is considered to be in the gaseous state
Note 1 to entry: The net heat of combustion is always smaller than the gross heat of combustion because the
heat released by the condensation of water vapour is not included.
−1
Note 2 to entry: The typical units are kilojoules per gram (kJ·g ).
[SOURCE: ISO 13943: 2008, 4.237]
3.20
oxidation
chemical reaction in which the proportion of oxygen or other electronegative element in a
substance is increased
Note 1 to entry: In chemistry, the term has the broader meaning of a process that involves the loss of an electron
or electrons from an atom, molecule or ion.
[SOURCE: ISO 13943: 2008, 4.245]
3.21
oxidizing agent
substance capable of causing oxidation

Note 1 to entry: Combustion is an oxidation.
[SOURCE: ISO 13943: 2008, 4.246]
3.22
oxygen consumption principle
proportional relationship between the mass of oxygen consumed during combustion and the
heat released
−1
Note 1 to entry: A value of 13,1 kJ·g is commonly used.
[SOURCE: ISO 13943: 2008, 4.247]
3.23
pyrolysis
chemical decomposition of a substance by the action of heat
Note 1 to entry: The term is often used to refer to a stage of fire before flaming combustion has occurred.
Note 2 to entry: In fire science, no assumption is made about the presence or absence of oxygen.
[SOURCE:ISO 13943: 2008, 4.266]
3.24
small-scale fire test
fire test performed on a test specimen of small dimensions
Note 1 to entry: A fire test performed on a test specimen for which the maximum dimension is less than 1 m is
usually called a small-scale fire test.
[SOURCE: ISO 13943: 2008, 4.292]
3.25
test specimen
item subjected to a procedure of assessment or measurement
Note 1 to entry: In a fire test, the item may be a material, product, component, element of construction, or any
combination of these. It may also be a sensor which is used to simulate the behaviour of a product.
[SOURCE: ISO 13943: 2008, 4.321]
4 Principles of determining heat release
4.1 Complete combustion measured by the oxygen bomb calorimeter
The most important device for measuring heats of combustion is the adiabatic constant
volume bomb calorimeter. The “bomb” is a central vessel which is sufficiently strong to
withstand high pressures so that its internal volume remains constant. The bomb is immersed
in a stirred water bath, and the combination of bomb and water bath is the calorimeter. The
calorimeter is also immersed in an outer water bath. During a combustion reaction, the
temperature of the water in the calorimeter and in the outer water bath is continuously
monitored and adjusted by electrical heating to the same value. This is to ensure that there is
no net loss of heat from the calorimeter to its surroundings, i.e. to ensure that the calorimeter
is adiabatic.
To carry out a measurement, a known mass of sample is placed inside the bomb in contact
with an electrical ignition wire. The vessel is filled with oxygen under pressure, sealed and
allowed to attain thermal equilibrium. The sample is then ignited using a measured input of
energy. Combustion is complete because it takes place in an excess of high pressure oxygen.

– 12 – IEC 60695-8-1:2016  IEC 2016
The heat released is calculated from the known heat capacity of the calorimeter and the rise
of temperature which occurs as a result of the combustion reaction.
The experiment gives the heat released at constant volume, i.e. the change in internal energy,
∆U. The gross heat of combustion is the enthalpy change, ∆H, where:
∆H=∆U+∆(PV)
where ∆(PV) is calculated using the ideal gas law;
∆(PV )=∆(nRT)
NOTE Bomb calorimeter measurement of the heat of combustion of building products is described in ISO 1716 [4].
4.2 Incomplete combustion
4.2.1 Measurement techniques
Combustion in fires, which usually occur in air and at atmospheric pressure, is almost always
incomplete and therefore the heat released will be less than the combined heats of
combustion of the materials involved.
The heat released can be determined indirectly using one of the following techniques:
a) oxygen consumption;
b) carbon dioxide generation;
c) gas temperature increase.
4.2.2 Heat release by oxygen consumption
For a large number of organic fuels, an approximately constant amount of heat is released per
−1
unit of oxygen consumed [5], [6]. The average value for this constant is 13,1 kJ·g of oxygen
and this value is widely used for practical applications both in small-scale and large-scale
testing. This relationship implies that it is sufficient to measure the oxygen consumed in a
combustion system, and the mass flow rate in the exhaust duct in order to determine heat
release.
Table 1 lists some net heat of combustion values [6]. With the exception of three materials:
ethene, ethyne and poly(oxymethylene), all the calculated heats of combustion per gram of
oxygen consumed lie between 12,5 kJ and 13,6 kJ. The values in Table 1 are calculated
assuming complete combustion. However, Huggett [6] does discuss the effects of possible
incomplete combustion and calculates values of ∆H for several such cases. For example, in
c
the case of cellulose burning to give a 9:1 ratio of CO2 to CO:

−1
(C H O ) + 5,7 O → 5,4 CO + 0,6 CO + 5 H O  ∆H = −13,37 kJ·g of O

6 10 5 2 2 2 c 2
or burning to give an appreciable amount of carbonaceous char:
−1
(C H O ) + 3 O → 3 CO + 3 C + 5 H O ∆H = −13,91 kJ·g of O

6 10 5 2 2 2 c 2
compared with complete combustion:
−1
(C H O ) + 6 O → 6 CO + 5 H O ∆H = −13,59 kJ·g of O

6 10 5 2 2 2 c 2
Huggett discusses several other examples and concludes that the assumption of a constant
heat release per unit of oxygen consumed will be sufficiently accurate for most applications.
If the correct value of ∆H per gram of O is known for a particular material then this shall be
c 2
used instead of the approximate value.
Table 2 lists some heat of combustion values for insulating liquids.
There is a variety of fire tests that use the oxygen consumption method. They vary from the
micro-scale, e.g. ASTM D 7309 [7], to the large-scale, e.g. EN 50289-4-11 [8].
Heat release fire tests that are of relevance to the testing of electrotechnical products are
described in IEC 60695-8-2.
4.2.3 Heat release by carbon dioxide generation
This technique is based on the concept that the energy released in a combustion reaction is
approximately proportional to the amount of carbon dioxide generated, provided that
combustion is complete or nearly complete (i.e. with very small CO/CO ratios). The average
−1
value for the proportionality constant is 13,3 kJ·g of carbon dioxide generated. If a more
accurate value is known for the material or product, it shall be used in calculating heat
release.
In general, heat release values determined by carbon dioxide generation agree well with heat
release rate values determined by oxygen consumption.
4.2.4 Heat release by increase of gas temperature
The gas temperature technique is based on the assumptions that there are no heat losses
and that all the heat generated by the fire is used to increase the temperature of the hot
flowing mixture of air and fire effluent, and that their temperatures can be determined
downstream from the flaming zone. If the heat losses, mainly from thermal radiation, are
negligible, then the gas temperature rise technique (also called the thermopile technique)
would represent the same heat release value as the oxygen consumption or the carbon
dioxide generation method. The heat release is determined by measuring the increase in the
temperature of the gases, at the thermopile, with respect to a reference temperature,
generally the ambient temperature. This is converted to heat release by means of
measurements of the total flow of the air and fire effluent mixture using the specific heat of
the mixture at the appropriate air temperature, or simply by calibration with a constant flow of
a material of well-known heat release, such as methane.
In general, heat release values determined by temperature measurement are lower than heat
release values determined by oxygen consumption or carbon dioxide generation calorimetry
techniques, because heat losses are generally not negligible. In a small-scale test, these heat
losses can, with care, be minimized by attempting to make the system as adiabatic as
possible.
A method of obtaining heat release values by temperature measurement has been developed
as ISO 13927 [22] which uses the same heating system and specimen mounting system as
ISO 5660-1 and can be used for production control and/or comparison purposes for research
and development. The test apparatus is both relatively easy to use and is of relatively low
cost.
– 14 – IEC 60695-8-1:2016  IEC 2016
−1
Table 1 – Relationship between heat of combustion expressed in units of kJ·g
−1
of fuel burned and kJ·g of oxygen consumed for a variety of fuels
a
∆H
c
Fuel Formula
−1 −1
kJ·g of fuel kJ·g of O
Methane (g) CH 50,0 12,5
Ethane (g) C H 47,5 12,7
2 6
Butane (g) C H 45,7 12,8
4 10
Octane (l) C H 44,4 12,7
8 18
Ethene (g) C H 47,1 13,8
2 4
Ethyne (g) C H 48,2 15,7
2 2
Benzene (l) C H 40,1 13,1
6 6
Polyethylene –(–C H –) – 43,3 12,6
2 4 n
Polypropylene –(–C H –) – 43,3 12,7
3 6 n
Polyisobutylene –(–C H –) – 43,7 12,8
4 8 n
Polybutadiene –(–C H –) – 42,7 13,1
4 6 n
Polystyrene –(–C H –) – 39,8 13,0
8 8 n
PVC –(–CH CHCl–) – 16 12
2 n
PMMA –(–C H O –) – 24,9 12,9
5 8 2 n
PAN –(–C H N–) – 30,8 13,6
3 3 n
Polyoxymethylene –(–CH O–) – 15,4 14,5
2 n
PET –(–C H O –) – 22,0 13,2
10 8 4 n
Polycarbonate –(–C H O –) – 29,7 13,1
16 14 3 n
Cellulose triacetate –(–C H O –) – 17,6 13,2
12 16 8 n
Nylon 66 –(–C H NO–) – 29,5 12,6
6 11 n
Cellulose –(–C H O –) – 16 13
6 10 5 n
Cotton – 15,5 13,6
Paper (newsprint) – 18,4 13,4
Wood (maple) – 17,7 12,5
Lignite – 24,8 13,1
Coal (bituminous) – 35,2 13,5
NOTE 1 (g) = gas, (l) = liquid.
NOTE 2 Most of the values in column 3 are calculated from thermodynamic data. The values in column 4 are
calculated from those in column 3 assuming complete combustion.
NOTE 3 For values calculated from thermodynamic data, carbon is assumed to be converted to carbon dioxide,
hydrogen to water, nitrogen to nitrogen dioxide and chlorine to hydrogen chloride.
a
Reactants and products at 25 °C, all products gaseous.

−1
Table 2 – Relationship between heat of combustion expressed in units of kJ·g
−1
of fuel burned and kJ·g of oxygen consumed for a variety of insulating liquids
a
∆H
c
Insulating liquids Formula
−1 −1
kJ·g of fuel kJ·g of O
Silicone oil (1) – 25 14,5
b
Pentaerythritol ester (2) – 36,8
Mixture of mono- and
b
– 39,5
dibenzyl toluene (3)
b
Paraffinic mineral (4) – 46,1
(1) Silicone transformer liquid, type T1, IEC 60836 [9]
(2) Transformer esters, type T1, IEC 61099 [10]
(3) Capacitor insulating liquid, IEC 60867 [11]

(4) Transformer and switchgear mineral oil, IEC 60296 [12]
NOTE Technical Committee 10 has found a range of values from different sources for the heat of combustion
−1 −1
of silicone oil of 25 kJ⋅g to 27 kJ⋅g .
a
Reactants and products at 25 °C, all products gaseous.
b
No data are currently available.

5 Parameters used to report heat release data
5.1 Heat of combustion (gross and net)
The standard heat of combustion of a substance is defined in thermochemical terms as the
enthalpy change that occurs when one mole of a substance undergoes complete combustion
under standard conditions. In the fire science community, heat of combustion is also referred
to as “gross heat of combustion”, and the units used are energy per unit mass rather than
energy per mole.
NOTE Older terms, now deprecated, are “calorific potential” and “gross calorific value”.
The water formed as a product of combustion is considered to be in the liquid state. For a
compound containing carbon and hydrogen, for example, complete combustion means the
conversion of all the carbon to carbon dioxide gas, and conversion of all the hydrogen to
liquid water.
Gross heat of combustion is measured by oxygen bomb calorimetry in which all the sample is
completely converted to fully oxidized products (see 4.1). In real fires this is rarely the case.
Some potentially combustible material is often left as char and products of combustion are
often only partly oxidized, for example, soot particles in smoke and carbon monoxide.
Net heat of combustion is similar to gross heat of combustion except that any water formed is
assumed to be in the vapour state. The difference is the latent heat of vaporization of water at
−1
298 K which is 2,40 kJ·g . Net heat of combustion is therefore always smaller than gross
heat of combustion. In flames and fire, water remains as vapour and therefore it is more
appropriate to use net heat of combustion values.
5.2 Heat release rate (HRR)
Heat release rate (see 3.16) is defined as the thermal energy released per unit time in a fire
or fire test. It is a particularly useful parameter because it can be used to quantify the
intensity of a fire.
– 16 – IEC 60695-8-1:2016  IEC 2016
Heat release rate is commonly reported in the form of a graph against time. A heat release
rate curve is shown in Figure 1.
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0 100 200 300 400 500 600 700
Time (s)
IEC
Figure 1 – Heat release rate (HRR) curve
5.3 Heat release (HR)
Heat release (see 3.15) is defined as the thermal energy that is produced in a fire or fire test.
It is a particularly useful parameter because it can be used to quantify the size of a fire. Heat
release is usually calculated by integration, with respect to time, of heat release rate data.
Figure 2 shows the curve calculated from Figure 1. However, usually only the total heat
release (see 5.5) is reported.
1 000
Total heat release = 900 kJ
0 100 200 300 400 500 600 700
Time (s)
IEC
Figure 2 – Heat release (HR) curve
5.4 Heat release rate per unit area (HRR*)
Sometimes, in the case of flat test specimens, heat release rate is reported in terms of the
−2
rate of heat release per unit area of the exposed surface. Typical units are kW·m .
NOTE Data from the cone calorimeter [13] are usually reported in this way [14].
A heat release rate per unit area curve is shown in Figure 3. (It is based on the curve of
Figure 1 assuming an exposed surface area of 100 cm .)

HR/kJ
HRR/kW
0 100 200 300 400 500 600 700
Time (s)
IEC
Figure 3 – Heat release rate per unit area (HRR*) curve
5.5 Total heat release
Total heat release is the heat release value at the end of the time period of interest. It can be
obtained by integrating the rate of heat release, usually from the time of ignition to the end of
the fire test. It can be used to quantify the size of a fire.
The total heat release in the curve of Figure 2 is 900 kJ.
5.6
...