ISO 24473:2008

INTERNATIONAL ISO
STANDARD 24473
First edition
2008-04-15
Fire tests — Open calorimetry —
Measurement of the rate of production of
heat and combustion products for fires of
up to 40 MW
Essais au feu — Calorimétrie ouverte — Mesurage de la vitesse de
production de chaleur et de produits de combustion dans le cas de feux
ayant un débit thermique inférieur ou égal à 40 MW

Reference number
©
ISO 2008
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Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Hood and exhaust duct . 3
5.1 Requirements of the hood/duct and extraction system . 3
5.2 Laboratory requirements . 3
6 Instrumentation of the exhaust duct . 3
6.1 General . 3
6.2 Volume flow rate . 3
6.3 Gas temperature . 4
6.4 Gas analysis . 4
6.5 Optical density . 5
7 Additional equipment and procedures . 5
7.1 Weigh platform . 5
7.2 Heat flux measurements . 5
7.3 Data recorder . 6
7.4 Timing device . 6
8 Heat and smoke release measurement . 6
9 Experimental arrangements . 6
10 Ignition sources . 6
10.1 General . 6
10.2 Calibration of gas burners . 7
11 System performance . 7
11.1 HRR measurement confirmation . 7
11.2 System response . 8
11.3 Precision . 8
12 Reliability of data . 8
13 Preparation of test specimens . 8
14 Testing . 9
14.1 Initial conditions . 9
14.2 Procedure . 9
15 Test report . 10
Annex A (informative) Design of the hood and exhaust system . 11
Annex B (informative) Instrumentation of the exhaust duct . 16
Annex C (informative) Procedure for checking the stability of the oxygen analyser . 18
Annex D (informative) Light measuring systems . 19
Annex E (informative) Calculations . 21
Annex F (informative) Ignition sources . 25
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Annex G (normative) Specific procedure for testing upholstered furniture . 27
Annex H (informative) Repeatability and reproducibility . 29
Bibliography . 30
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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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 24473 was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 1, Fire initiation
and growth.
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.
vi
INTERNATIONAL STANDARD ISO 24473:2008(E)
Fire tests — Open calorimetry — Measurement of the rate of
production of heat and combustion products for fires of up to
40 MW
WARNING—So that suitable precautions can be taken to safeguard health, the attention of all
concerned in fire tests is drawn to the possibility that toxic or harmful gases can be evolved during
combustion of test specimens.
The test procedures involve high temperatures. Hazards can therefore exist for burns and ignition of
extraneous objects or clothing. The operators should use protective clothing, helmets, face-shields and
breathing equipment for avoiding exposure to toxic gases.
Laboratory safety procedures should be set up to ensure the safe termination of tests. Adequate means
of extinguishing such a fire must be provided.
Specimen collapse may also occur in the laboratory space. Laboratory safety procedures should be set
up to ensure safety of personnel with due consideration to such situations.
1Scope
This International Standard specifies a series of test methods that simulate a real scale fire on a test object or
group of objects under well-ventilated conditions. A range of different fire sizes can be studied according to the
scale of the equipment available.
The method is intended to evaluate the contribution to fire growth provided by an object or group of objects
using a specified ignition source.
A test performed in accordance with the method specified in this International Standard provides data for all
stages of a fire.
NOTE When the data are used in relation to specific situations the effect of the environment, including the effects of
feedback and restricted ventilation, needs to be taken into account.
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.
ISO 5660-1, Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 1: Heat
release rate (cone calorimeter method)
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
ISO 9705:1993, Fire tests — Full-scale room test for surface products
ISO 13784-1, Reaction-to-fire tests for sandwich panel building systems — Part 1: Test method for small rooms
ISO 13784-2, Reaction-to-fire tests for sandwich panel building systems — Part 2: Test method for large rooms
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ISO 13785-1, Reaction-to-fire tests for façades — Part 1: Intermediate-scale test
ISO 13943, Fire safety — Vocabulary
ISO/TS 14934-1, Fire tests — Calibration and use of radiometers and heat flux meters — Part 1: General
principles
ISO 14934-2, Fire tests — Calibration and use of heat flux meters — Part 2: Primary calibration methods
ISO 14934-3, Fire tests — Calibration and use of heat flux meters — Part 3: Secondary calibration method
ISO/TS 14934-4, Fire tests — Calibration of heat flux meters — Part 4: Guidance on the use of heat flux meters
in fire tests
ISO 19702, Toxicity testing of fire effluents — Guidance for analysis of gases and vapours in fire effluents using
FTIR gas analysis
EN 13823, Reaction to fire tests for building products — Building products excluding floorings exposed to the
thermal attack by a single burning item
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
3.1
assembly
fabrication of materials and/or composites, e.g., sandwich panel systems
3.2
material
single substance or uniformly dispersed mixture, e.g., metal, stone, timber, concrete, mineral fibre or polymers
3.3
product
material, composite or assembly about which information is required
3.4
test specimen
representative piece of the product that is to be tested together with any substrate or treatment
NOTE The test specimen may include an air gap.
4Principle
The potential for the contribution of a single object or group of objects to the hazard of heat release and spread
of fire, without being influenced by the effects of any surrounding structure, is evaluated over the period of
combustion using a calorimeter. The rate of heat release of the fire is based on calculation of oxygen
consumption.
NOTE 1 Procedures to determine the heat release rate (HRR) based on the rate of production of carbon dioxide, can also
be used, but are not covered in this International Standard.
The hazard of reduced visibility is estimated by the measurement of the production of light-obscuring smoke.
The fire growth is visually documented by photographic and/or video recording.
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NOTE 2 The procedure can be extended to include measurement of:
— time-related weight loss of the fuel;
— the incident heat flux or surface temperature at positions in the vicinity of the fire, as an indication of the hazard of fire
spread to an adjacent object;
— the rate of production of certain gaseous combustion products under well-ventilated conditions, using appropriate
analytical procedures for gases, as input to data for studies of toxicological hazards.
5 Hood and exhaust duct
5.1 Requirements of the hood/duct and extraction system
The hood and duct system shall be large enough in terms of the size of the hood and the air throughput of the
system to ensure that all the combustion products are collected. It shall be at a height such that the flames do
not impinge on the hood itself.
NOTE 1 The principles of the design and operation of a hood and duct system and examples of designs in use are given in
Annex A.
The system shall not disturb the fire-induced flow at the fire itself.
NOTE 2 This can be demonstrated by carrying out tests with a gas burner at different flow rates in the proposed operating
range to show that the HRR data are independent of the setting of the exhaust system (for example as outlined in 11.3).
5.2 Laboratory requirements
The equipment shall be positioned in a laboratory and placed so as to avoid the effects of reflected radiation
from walls and to allow free inflow of air. For fires of up to 1MW, the open sides of the calorimeter hood shall be
at least 2m from the nearest walls. For larger fires this shall be increased; up to 10 m for fires of 20 MW.
The ambient air temperature in the laboratory shall be recorded at intervals of 3s or less. This is necessary
because the operation of the flow system will cause replacement of a quantity of air within the laboratory in
which it is installed.
NOTE The number of air changes per hour will be dependent upon the size of the room and the volume flow rate of the
calorimeter. It is necessary to provide adequate ventilation to prevent negative pressure.
6 Instrumentation of the exhaust duct
6.1 General
The following sub-clauses specify minimum requirements for instrumentation in the exhaust duct.
NOTE Additional information and designs can be found in Annex B.
6.2 Volume flow rate
The volume flow rate in the exhaust duct shall be measured to an accuracy of at least ±5%.
The response time of the barometric instrument that measures flowrate shall be a maximum of 1s for a change
from 10 % to 90 % of the difference between the initial and final differential pressure.
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6.3 Gas temperature
The temperature of the gas in the duct shall be measured using a 1,0 mm to 1,6 mm outside diameter, sheathed
thermocouple supported in a position in the vicinity of the bi-directional probe. The thermocouple should not be
allowed to disturb the flow pattern around the bi-directional probe.
It is recommended to provide more than one thermocouple in case one should fail during the test.
6.4 Gas analysis
6.4.1 Sampling line
The gas samples shall be taken in the exhaust duct at a position where the combustion products are uniformly
mixed and down stream of the flow probe and the temperature probe. The sampling line shall be made from an
inert material that will not influence the gas species to be analysed. The gas samples shall be taken across the
whole diameter of the duct. If a single sampling point is used, samples shall be taken across the duct at this
axial position to demonstrate that the concentration across the duct is within ±2% of the average value as
determined by probe traverses. The sample gas shall pass through particulate filters and a cooler, then through
a cell containing anhydrous calcium sulfate drying agent, under the influence of an oil-free diaphram pump,
before being distributed to the different analysers.
NOTE An example of an arrangement is given in Figure B.1. One material which can be used to construct the sampling line
is PTFE. The ratio of sampled to analysed gas is normally at least 20. However, it is more important that the system be
designed as a whole in order to optimise system response as described in 11.2.
6.4.2 Oxygen
The O analyser shall be of the paramagnetic type or equivalent in performance and capable of measuring a
range of at least 0% to 21 % (volume percent) oxygen.
volume of gas×100
volume percent =
volume of air
The accuracy of the oxygen measurement shall be ± 0,02 % by volume oxygen or less (i.e. ± 0,00 2 % volume
fraction oxygen or less). The noise and drift of the analyser shall be not more than 100 ppm (0,01 % by volume)
over a period of 30 min (measured as specified in Annex C). The output from the analyser and the data
acquisition system shall have a resolution of 0,01 % by volume oxygen or better. The HRR value is most
sensitive to the oxygen measurement, therefore the performance of the oxygen meter shall exceed the overall
requirements for system response and accuracy.
6.4.3 Carbon monoxide and carbon dioxide
The gas species shall be measured using analysers with an accuracy of ± 0,05 % by volume or less (i.e.
± 0,000 5 volume fraction or less) for carbon dioxide and ± 0,001 % by volume or less (i.e. ± 0,000 01 volume
fraction or less) for carbon monoxide.
The HRR value is also sensitive to the carbon dioxide and carbon monoxide measurements, therefore the
performance of the carbon dioxide and carbon monoxide meters shall exceed the overall requirements for
system response and accuracy.
6.4.4 Measurement of other combustion gas components
When required by the sponsor or regulator, this shall be carried out for a range of different gaseous components
using FTIR spectroscopic techniques described in ISO 19702 or other techniques of gas sampling and analysis.
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6.5 Optical density
The optical density of the smoke shall be determined by measuring light obscuration using a white light system
or a laser system.
EXAMPLE 1 A white light system could consist of a lamp, lenses, an aperture and a photocell (see Annex D).
For a white light system the detector shall have a spectrally distributed responsivity in agreement with the CIE
(Commission Internationale d'Éclairage), V (γ)-function, the CIE photopic curves to an accuracy of at least
±5%.
EXAMPLE 2 A laser system could be one based on the use of a He-Ne laser light source (see Annex D).
The equipment shall be constructed in such a way as to ensure that soot deposited during the test does not
reduce the light transmission by more than 5%. The light beam shall cross the exhaust duct along its diameter
at a position where the smoke is homogenous. The detector output shall be demonstrated to be linear within
5% over the range of output to be used.
7 Additional equipment and procedures
7.1 Weigh platform
The electronic output of the weigh platform shall be logged with the same frequency and on the same time base
as the other logged data.
The platform shall be sufficiently protected from the fire that the output is unaffected by heat from the fire and
shall be capable of retaining all the liquid and solid products of combustion.
NOTE This can be achieved by covering the platform with a sheet of calcium silicate board of at least 12,7 mm thickness
supported, if necessary, by a metal framework. If necessary, a shallow metal tray, capable of holding the test arrangement,
should also be used.
In order to avoid the effect of an up thrust on the measured weight induced by the fire, the ingress of air below
the weigh platform shall be prevented on all four sides by the fitting of low walls (screens).
Each day of testing, the platform shall be checked over the range of weight loss expected using standard
1%
weights. The output shall be accurate to of the expected range of mass loss or better.
7.2 Heat flux measurements
7.2.1 General
Measurements of incident heat flux may be made at specific positions in the vicinity of the burning item to
provide information on the possibility of ignition of a wall surface or a secondary item.
7.2.2 Specification
The heat flux meter shall be of the Gardon (foil) or the Schmidt-Boelter (thermocouple) type with a design range
−2
of about 50 kW m . Schmidt-Boelter gauges are recommended when the convective currents are expected to
◦
be significant. The target area shall be a flat, black surface having an acceptance angle of 180 . The heat flux
meter shall have an accuracy of at least ±3% and a repeatability value within 0,5 %. In operation, the meter
◦
shall be maintained at a constant temperature (within ± 5 C) above the dew point of the combustion products.
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7.2.3 Calibration
The calibration and use of heat flux meters shall be in accordance with ISO/TS 14934-1, ISO 14934-2,
ISO 14934-3 and ISO/TS 14934-4.
NOTE Attention is drawn to the fact that measurements of total heat flux such as those described above will comprise a
convective component as well as a radiative component, and the magnitude of the latter will depend on test conditions
including geometry. Consequently the results can only be valid in relation to the geometry of the test.
7.3 Data recorder
A data logger capable of recording and storing input data from all instruments at intervals not exceeding 3s
shall be provided, and this frequency shall apply to all logged measurements.
7.4 Timing device
A clock with 1s divisions or an equivalent timing device shall be provided.
8 Heat and smoke release measurement
The calculation of rate of heat release (HRR) and the rate of smoke production shall be in accordance with the
procedures given in Annex E.
NOTE Annex E also contains procedures for the calculation of other parameters.
9 Experimental arrangements
The test item or the test arrangement should be placed centrally below the hood. Items should be positioned as
in use. For example, furniture may be placed directly on the floor or on a weigh platform, a television set may be
placed on a table, curtains may be hung on a rail and electronic equipment or books may be placed in suitable
racks.
A specific procedure for the testing of upholstered furniture is given in Annex G. (It should be noted that other
procedures are available using different burners.)
When investigating the fire behaviour of a system, it is critical to understand the contributions of the different
components. It may be necessary to conduct heat release rate experiments on the individual components in
addition to the entire system.
NOTE Advice on the measurement range of the calorimeter in relation to the size of the fire is given in 5.1 and Annex A.
However, it is also necessary to ensure that the maximum heat release rate is not in the lower part of the measuring range
of the calorimeter, under which circumstances the uncertainty of measurement would be high (low oxygen depletion). For
this reason the ISO 9705 calorimeter system, for example, is unsuitable for measurements on fires with a maximum HRR of
less than 50 kW.
10 Ignition sources
10.1 General
The ignition source should be equivalent in size, positioning and heating characteristics (e.g. flame or radiant,
luminous flame or premixed flame) to the type of ignition that forms the basis of the hazard examined.
Information on ignition sources detailed in existing standards and the use of ignition sources are given in
Annex F.
The position of the heat source in relation to the test specimen shall be recorded.
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Baseline HRR measurements for the ignition source shall be collected.
For gas burner sources, the heat of combustion of the gas from the local supply shall be known, as well as the
uncertainty of the measurement. The gas flow to the burner shall be controlled with an accuracy of at least
±3%. The heat output from the burner shall be controlled within ±5% of the prescribed value.
WARNING — The operating of gas burners should only be carried out with the appropriate safety
precautions.
10.2 Calibration of gas burners
The calibration of a mass flow controller shall be renewed at least annually. Alternatively, the system shall be
checked at least bi-annually by one of the following methods, giving agreement to within 2%.
1) Use of “in-line” wet or dry calibrated gas meter.
2) Mass loss of gas from liquid supply tank (with vaporizer) or from cylinders.
NOTE This requires a suitable system for weighing the gas supply and a flexible connection between the gas supply and
the metering system. The influence of the flexible connection on the mass change needs to be negligible and it is recognised
that the method may not be suitable in all cases. It is necessary to demonstrate that the mass loss equals the fuel burning
rate and no procedure is at present available for doing this.
The safety aspects of this procedure need to be considered as, in some countries, flexible connections may not
be used and the gas container will need to be disconnected for weighing.
11 System performance
11.1 HRR measurement confirmation
An HRR measurement confirmation test shall be performed prior to each test or continuous series of tests.
NOTE 1 The calculation procedures required are given in Annex E.
NOTE 2 When operating a calorimeter in which flowrate is determined using an orifice plate device, the results of a test of
this type are often used to derive the orifice plate constant, and in such cases cannot be used to confirm the HRR
measurement.
For calorimeter installations conforming to ISO 9705, the confirmation test shall be performed with the burner
heat outputs given in Table1, with the burner positioned directly under the hood of the calorimeter.
Measurements shall be taken at least every 3s and shall be started 1 min prior to ignition of the burner.
For other installations, the measurements shall be made in the same way, but the higher level of HRR should be
at least 30 % of the range of HRR for which data are to be used and the lower level shall be one third of the
higher level.
At steady state conditions, the difference between the mean heat release rate over 1 min, calculated from the
measured oxygen consumption and that calculated from the metered gas input shall not exceed 10 % for each
level of heat output.
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Table 1 — Burner heat output profile for ISO/TR 9705-2 calorimeter
Time Heat output
min kW
0 to 2 0
2 to 7 100
7 to 12 300
12 to 17 100
17 to 19 0
NOTE HRR measurement confirmation at higher levels can be performed to decrease the measuring uncertainty. This can
be carried out using gas burners, liquid pool fires or liquid spray burners (Reference [5]). A suitable burner and metering
system using natural gas and capable of being used for fires of up to 6MW has been described (Reference [6]). As an
example of a liquid fuel pool fire, methanol or n-heptane is burned in a flat stainless steel container of a suitable size. For
pool fires a comparison should be made of the measured net effective heat of combustion measured over the period from
19,94 MJ/kg 44,56 MJ/kg
ignition to flame-out with a published value for the same fuel (methanol , heptane ) (Reference [7]).
For methyl alcohol, a combustion efficiency of 96 % should be used.
11.2 System response
The “delay time”, the “response time” and the “duct flow time” are based on the signals from the oxygen and
carbon dioxide analysers and the duct temperature measuring instrument, and shall be calculated from the step
change data obtained in the test described in 11.1.
The delay time for any step shall be taken as the difference between the time at which the duct gas temperature
◦
changes by 2,5 C and the time when the oxygen mole fraction has changed by 0,000 5 or the carbon dioxide
mole fraction has changed by 0,000 2. For the first step change from low to high level, this shall be 30 s or less
for both analysers. These delay times shall be used to correct all test data (see E.2.2).
The response time of the oxygen or carbon dioxide gas analyser shall be taken as the time taken during any
step in the system check between a 10 % and 90 % response to the change being made. For the first step
change from low to high level this shall be 15 s or less for both analysers.
The duct flow time shall be taken as the difference between the observed time of ignition and an increase of
◦
2,5 C in the duct gas temperature. This shall be used to correct all data in relation to the start of the test
(see E.2.2). For the first step change from low to high level, it shall be 9s or less.
The time for a 90 % step change in the fuel supply shall be 2s or less.
NOTE Fast radiometers around the heat source are independent measures of the step change.
11.3 Precision
The system shall be checked at various volume flow rates by increasing the volume flow in the exhaust duct in
four equal steps, over the range of flow settings to be used [for an ISO 9705 installation these steps shall be
2 −1 ◦
from 2m s (at 0,1 MPa and 25 C) up to the maximum]. The heat output from the burner shall be the higher
level used in 11.1. The discrepancy in the mean heat release rate, calculated over 1 min, shall be not more than
10 % of the actual heat output from the burner.
12 Reliability of data
This is discussed in Annex H.
13 Preparation of test specimens
13.1 The product to be tested shall, as far as possible, be placed in the same way as in practical use.
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13.2 Unless hydroscopic, specimens shall be conditioned to equilibrium in an atmosphere of (50± 5) %
relative humidity at a temperature of (23± 2) %. Equilibrium shall be deemed to be reached when the item has
achieved constant mass.
Constant mass is considered to be reached when two successive weighing operations, carried out at an interval
of , do not differ by more than of the mass of the test piece or , whichever is the greater.
24 h 0,1 % 0,1 g
13.3 Full details of the test specimen shall be obtained (and those of any secondary items), including
composition, dimensions, manufacturer and manufacturer's model number and reference. If relevant, details of
component parts shall also be given.
NOTE In the case of furniture this includes the mass, composition and constructional details of the cover, the interliner (if
any), the filling material and the framework.
14 Testing
14.1 Initial conditions
◦ ◦
14.1.1 The temperature in the test facility at the start of the test shall be between 10 C and 30 C.
14.1.2 The horizontal wind speed measured at a horizontal distance of 1m from the specimen shall not
−1
exceed .0,5 m s
14.1.3 The ignition source shall be placed in the required position. Full details of the geometry of the test
set-up shall be recorded.
14.1.4 The test arrangement shall be assembled centrally under the hood of the calorimeter.
14.1.5 The test arrangement shall be photographed or video recorded prior to testing.
14.2 Procedure
14.2.1 Start all recording and measuring devices and record data for at least 2 min prior to ignition of the
burner.
14.2.2 Ignite the burner and adjust it to the required output levels. Adjust the exhaust capacity so that all
combustion products are collected. Changes should be made slowly to avoid adverse effects on the delay
times.
14.2.3 Make a photographic and/or video recording of the test. A clock shall appear in all photographic
records, giving time to the nearest 1s.
14.2.4 During the test, make a record of observations and the times when they occur.
14.2.5 End the test when the combustion has become insignificant, and normally after 30 min if no significant
combustion has developed. A decision to continue beyond this time should only be made if it is expected that
the effects of instrument drift are insignificant and that the final conditions (see 14.2.8) can be met.
14.2.6 The test may need to be terminated earlier if structural collapse or other conditions develop which are
potentially dangerous to the laboratory staff. Continue observation until signs of visual combustion have ceased
or the test is ended.
14.2.7 Report the extent of damage of the product after the test.
14.2.8 After extinction of the fire and/or removal of the test materials and debris, the final oxygen analyser and
carbon dioxide analyser readings should be within 0,02 % by volume (0,000 2 volume fraction) of the initial
values and the light meter attenuation shall be less than 2% of full range. If this is not the case, it should be
reported in the test report and an error analysis should be conducted. In certain cases the data can be invalid.
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For some large scale tests it may not be practical to extinguish and remove the residues in a short time at the
end of a test and in such cases the reasons for omitting this procedure should be reported.
14.2.9 Record any other unusual behaviour.
15 Test report
The test report shall contain the following information:
a) name and address of the testing laboratory;
b) date and identification number of the report;
c) name and address of the sponsor;
d) purpose of the test;
e) method of sampling;
f) name and address of manufacturer or supplier of the product;
g) name or other identification marks and description of the product;
h) construction and installation details of the product:
1) drawings;
2) descriptions;
3) assembly instructions;
4) specification of materials of construction;
5) details of the joints and fixings;
i) date of supply of the product;
j) date of test;
k) test method used and reference to this International Standard, i.e., ISO 24473:2008;
l) conditioning of the test specimen, environmental data during the test (temperature, atmospheric pressure,
relative humidity, etc.);
m) deviations from the test method, if any;
n) test results:
1) observations during and after the test;
2) the graphical output of time/volume flow in the exhaust duct (optional);
3) the graphical output of time/rate of total heat release and time/heat release from the burner;
4) the graphical output of time/production of carbon monoxide at reference temperature and pressure
(optional);
5) the graphical output of time/production of carbon dioxide at reference temperature and pressure
(optional);
6) the graphical output of time/rate of mass loss (if carried out);
7) the graphical output of time/production of light-obscuring smoke at actual duct flow temperature.
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Annex A
(informative)
Design of the hood and exhaust system
1)
A.1 Design and operation of a full-scale hood and duct system for open calorimetry
The hood, duct and exhaust system are the basis of the calorimeter and the size of these depends on the size
of the fire being studied. In general, the same instrumentation set can be used for any level of measurement.
The straight section of the exhaust duct in front of the measuring section (the section containing the pressure
probe, thermocouple, sampling tube and light measurement system) should be at least ten duct diameters in
length in order to achieve effective mixing of the combustion products. In order to ensure a more uniform flow
profile across the duct, it is also necessary to continue the straight section of the duct for up to five duct
diameters beyond the measuring section of the duct and before the extraction fan.
In a most accurate mode of operation, the mean reach of the flames should not extend above the inlet plane of
the hood. Experience has shown that, in this mode, the calorimeter does not affect the yield of fire products. In
a less accurate mode of operation, flames are allowed to extend above the inlet plane of the hood and it is then
possible to measure higher heat release rates with the calorimeter without much loss in accuracy, at least for
combustibles with fairly high combustion efficiency. However, in this mode concentrations of fire gases
associated with incomplete combustion, such as CO, have been seen to increase. It should be noted that fitting
extensions to the hood may not be good practice if their presence encourages conducting test fires so large that
smoke descends into the extension region.
The volume of the hood should be as small as possible in order to minimize the “hold-up” of combustion gases
in the hood, which produces a time lag and smear in gas concentrations reaching the calorimeter analysis
station. However, the inlet area must be large enough to collect the plume gases. A conical hood is much
.
preferred to other designs. For an arbitrary calorimeter capacity Q, in kilowatts, a near-optimum inlet diameter
of a conical hood (or inlet side of a box hood) can be scaled according to:
.
2/5
Inlet diameter (metres)=[Q/20 000] × 10,7 (A.1)
The clearance of the rim of the inlet cone above the base of the combustible (which may or may not be at the
floor of the test building) should be at least as large as the greatest expected flame height. If this is not known,
the clearance height can be scaled according to:
.
2/5
Clearance height (m)=[Q/20 000] × 11,3 (A.2)
It is normally necessary to use a hood of fixed height and this recommendation may not therefore be achieved
without the use of staging.
In the “less accurate mode”, with flames reaching the top of the hood, heat release rates considerably greater
than the nominal calorimeter capacity (“most accurate mode”) can be accommodated, perhaps by a factor of
two.
The duct flow rate should be large enough to limit the temperature rise (from ambient) in the duct to a
reasonable value for the design capacity, suggested as 105 K. This insures that operation in the “less accurate
mode,” with flames reaching the top of the hood, does not lead to excessive temperature rise, which should
remain within 210 K. The maximum required duct flow can be scaled from:
.
Maximum duct flow (kilograms per second)=[Q/20 000]× 136 (A.3)
1) Information supplied by G. Heskestad, FM Global.
©
ISO 2008 – All rights reserved 11

The duct diameter should be small enough to create sufficiently high duct velocities to prevent temperature
stratification in the duct, yet not so small that pressure drops are excessive. Duct diameters can be scaled
(corresponding to a cold velocity of 15,6 m/s) from:
.
1/2
Duct diameter (metres)=[Q/20 000] × 3,05 (A.4)
A.2 Existing designs of hood/duct system
A.2.1 General
Information on some large calorimeters currently in use is given in Table A.1. (These may not have been built
using the design guidelines referred to in Clause A.1.)
Table A.1 — Details of existing large calorimeter installations in use
Height of hood
Diameter Method of flow Maximum Shape of hood Description of
Duct shape opening above
of duct measurement flow rate opening hood opening
ground
3 −1
(m) (m s ) (m)
Bi-directional
Circular 1,4 43 Square 9m×9m sides 5
a
probe/profile
Bi-directional 8 to 12
Circular 1,0 20 Conical 6m diameter
a
probe/profile (variable)
9m× 12 m
6 bi-directional
Circular 1,52 No data Rectangular 3
probes sides
b
Circular 3,08 4 pitot tubes 108 Conical 9,24 m diameter 9,24
a
Single probe + flow profile data.
b
Probes equally spaced on circle at 2/3 radius normal to flow with a wall static pressure tap.
©
12 ISO 2008 – All rights reserved

A.2.2 Details of the hood and duct system of the ISO 9705 calorimeter
Dimensions in millimetres
Key
1 guide vanes
2 bi-directional probe
3 guide vanes
4 lamp, photocell system
5 gas analysis
6 exhaust duct ∅ 400 mm
7 opening 3 000 mm× 3 000 mm
8 frame of steel profile 50 mm× 100 mm× 3,2 mm
9 steel plates 1 000 mm× 3 000 mm
10 steel plates 2mm× 500 mm× 900 mm
11 hood of 2mm thick steel plates
12 four steel plates 395 mm× 400 mm
a
To exhaust gas cleaning.
Figure A.1 — Schematic diagram of the exhaust system and location
of sampling probes for the ISO 9705 calorimeter
The ISO 9705 system uses a full-scale calorimeter that has been standardized. It comprises a duct of diameter
0,4 m and a hood with a 3m×3m square opening connected by a mixing chamber. The mixing chamber is not
essential for open calorimetry tests (but is necessary for room tests). It has been found to be suitable for
studying the burning behaviour of medium sized objects such as furniture and sections of construction with a
maximum heat release of between 1MW and 2MW. It should be noted that, in accordance with Clause A.1, an
3 −1
exhaust duct flow rate of 6,8 m s would be required for the most accurate measurements at a level of 1MW.
3 −1
This is almost twice that required in the standard itself (3,5 m s ).
©
ISO 2008 – All rights reserved 13

A.2.3 Details of a 7,5 MW calorimeter installation (Reference [8])
Dimensions in metres
Key
A 0,884 m diameter orifice.
B Laboratory attic space.
C 1,524 m diameter duct.
D Calorimeter station.
E Poured concrete floor.
F Suspended ceiling.
G Air inlet louvers.
H Calorimetry laboratory space.
Figure A.2 — Schematic diagram of a 7,5 MW calorimeter
6,096 m
The fire calorimeter, consists of a collection cone of 304 stainless steel, in diameter at its lowest point,
which is 7,925 m above the concrete floor of the laboratory. Attached to the top of the cone is a 1,524 m inner
diameter 304 stainless steel duct, which elbows from the cone and eventually joins into the exh
...