ISO 21843:2018

INTERNATIONAL ISO
STANDARD 21843
First edition
2018-09
Determination of the resistance
to hydrocarbon pool fires of fire
protection materials and systems for
pressure vessels
Détermination de la résistance aux feux de nappe d'hydrocarbure
des matériaux et systèmes de protection incendie des récipients sous
pression
Reference number
ISO 21843:2018(E)
©
ISO 2018

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ISO 21843:2018(E)

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© ISO 2018
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Published in Switzerland
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ISO 21843:2018(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Principle . 4
6 Test equipment. 4
6.1 General . 4
6.2 Burner arrangement . 4
6.3 Fuel supply for burners . 4
6.4 Test fluids . 5
6.5 Test building . 5
7 Calibration tests . 5
7.1 General requirements . 5
7.2 Calibration test vessel construction . 5
7.3 Calibration test procedure . 7
7.4 Analysis of calibration tests . 8
7.5 Requirements for successful calibration tests . 9
7.6 Environmental conditions .10
7.7 Tolerances .10
7.8 Calibration report .11
8 Construction of fire test specimens .11
9 Instrumentation .12
10 Fire protection materials and systems .13
10.1 General .13
10.2 Applied fire protection materials .13
10.3 Assemblies and mounted fire protection systems .15
11 Test procedure .15
12 Termination of the test .16
13 Repeatability and reproducibility .16
14 Uncertainty of measurement .16
15 Test report .16
16 Practical application of test results .17
16.1 Pressure relief valve (PRV) .17
16.2 Propane (or alternative test fluid) fill level .17
17 Performance criteria .18
17.1 General .18
17.2 Substrate temperature .18
17.3 Coatings and spray-applied materials .18
17.4 Systems and assemblies .18
18 Factors affecting the validity of the test .19
18.1 Interruption of the test .19
18.2 Failure of thermocouples and DFTs .19
18.3 Failure of pressure transducers .19
18.4 Test related tube and pipe .19
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ISO 21843:2018(E)

18.5 Variation in environmental conditions .20
18.6 Directional flame thermometer (DFT) results .20
19 Recommended classification procedures .20
19.1 General .20
19.2 Type of fire .20
19.3 Type of application .20
19.4 Classification based on temperature rise and period of resistance .21
19.5 Classification based on duration before failure .21
Annex A (informative) Example P&I diagram for test facility .22
Annex B (informative) Directional flame thermometers (DFTs) .23
Annex C (normative) Method of affixing thermometers .24
Annex D (informative) Radiation convection balance .25
Annex E (informative) Additional classification procedures: Classification based on
duration before failure .30
Bibliography .35
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ISO 21843:2018(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire
containment.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO 21843:2018(E)

Introduction
This document describes a test procedure to assess the protection afforded by fire protection materials
and systems to pressure vessels. It gives an indication of how fire protection materials perform when
exposed to a set of specified fire conditions. Actual vessels can vary in construction from that tested
and can utilise additional protection systems. The test conditions have been shown to be representative
of the severity of unconfined pool fires fuelled by light and medium oil distillates such as LPG and
petroleum products.
Test laboratories should be aware of the significant potential hazards involved in pressure vessels
testing. Facilities intending to undertake tests in accordance with this document should be designed to
be safe in the event of vessel failure.
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INTERNATIONAL STANDARD ISO 21843:2018(E)
Determination of the resistance to hydrocarbon pool fires of
fire protection materials and systems for pressure vessels
1 Scope
This document specifies a test method for determining the fire resistance of pressure vessels with a
fire protection system when subjected to standard fire exposure conditions. It does not address vessels
cooled by water deluge or water monitor. The test data thus obtained permits subsequent classification
on the basis of the duration for which the performance of the pressure vessel under these conditions
satisfies specified criteria. The design of the pressure vessel is not covered in this document.
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.
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp3 .1
3.1
blowdown valve
BDV
blowdown device
valve or device that opens to depressurize a pressure vessel
EXAMPLE Fusible plug.
3.2
burner arrangement
configuration of the equipment designed to engulf the test specimen in fire, with specific reference to
the size, orientation, frequency and spacing of burner heads, and the design of fuel supply piping
3.3
burst pressure
calculated burst pressure
pressure that gives a hoop stress equal to the ultimate strength of the vessel material at the
specific wall temperature of interest
Note 1 to entry: For long duration tests, stress rupture analysis is also considered a realistic failure mode.
3.4
calibration test
test performed by the laboratory prior and separate to customer tests, to confirm that the chosen burner
arrangement in combination with the desired test specimen conforms with the required conditions of
this document
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ISO 21843:2018(E)

3.5
critical pressure
pressure calculated for a given critical wall temperature as the burst pressure divided by a factor of
safety (FOS)
3.6
critical temperature
design limiting temperature, or a specified limiting wall temperature, that the vessel wall temperature
shall not exceed during fire exposure
Note 1 to entry: This temperature is related to a factor of safety (FOS) for the vessel when exposed to fire.
3.7
directional flame thermometers
DFTs
passive thermocouple based sensors that can be used for the measurement of both temperature and
heat flux
Note 1 to entry: Various designs are available. A simple design is described in this document.
3.8
factor of safety
FOS
ratio of the calculated ultimate strength of the vessel steel at the temperature of interest (e.g. critical
temperature) divided by the actual hoop stress in the vessel
Note 1 to entry: A typical FOS is in the range 2 to 3.
3.9
fire protection system
thermal protection system
protection afforded to the vessel to reduce the rate of heat transfer from the fire to the vessel, throughout
the period of exposure to fire, including any protection materials together with any encasement (such
as a jacket), and supporting system (such as mesh reinforcement or framing system) and any specified
primer and top coat if applicable
Note 1 to entry: Often referred to as a thermal protection system in North America.
3.10
pool fire
hydrocarbon diffusion fire that occurs over a static or flowing release of flammable liquids
Note 1 to entry: It simulates large turbulent diffusion flames that are strongly radiating.
3.11
pressure relief valve
pressure safety valve
PRV
pressure-activated valve intended to limit pressure rise to a specified value
Note 1 to entry: These valves have set opening and reclosing pressures.
3.12
pressure vessel
vessel capable of containing pressures significantly above ambient, even if normal operational
procedure does not involve pressure rise above ambient
Note 1 to entry: Pressure vessels are often referred to as vessels or tanks.
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ISO 21843:2018(E)

3.13
radiation-convection balance
fraction or percentage of total heat transfer to a cool surface that is due to radiation
Note 1 to entry: The cool surface may be a water-cooled calorimeter at a temperature of up to 100 °C.
3.14
test related tube and pipe
additional tube or pipe added to the vessel for the purposes of performing tests
Note 1 to entry: They may not be present on the real application tank.
3.15
total containment pressure vessel
pressure vessel that has no automatic means of pressure relief or depressurization
3.16
ullage space
vapour-filled space at the top of the vessel, where there is no liquid contact with the wall
3.17
vessel shell
primary wall of the vessel
4 Symbols and abbreviated terms
A area
f radiation fraction
rad
T temperature
t time
m mass
−2
q net absorbed heat flux (W.m )
net
q heat flux due to convection
conv
q Heat flux due to radiation
rad
ε emissivity
−8 −2 −4
σ Stefan-Boltzmann constant (5,67 × 10 W.m .K )
Subscript terms
cal calorimeter
DFT directional flame thermometer
f fire
indic indicated
s substrate
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ISO 21843:2018(E)

5 Principle
The method provides an indication of how vessels protected with fire protection materials or systems
perform when exposed to pool fires on solid surfaces. It simulates the thermal loads to a vessel engulfed
in a large pool fire through the use of burners to create a flame capable of engulfing a vessel. To ensure
that suitable test conditions are achieved and maintained, it describes calibration tests to be performed
prior to fire testing, sets permitted tolerances from the calibrated set-up, and delimits environmental
conditions.
6 Test equipment
6.1 General
The test procedure is intended to simulate a liquid hydrocarbon pool fire that achieves a heat flux to a
2 2
cool surface of 90 kW/m to 120 kW/m .
NOTE The literature suggests that heat flux to a cool surface in a large pool fire is 80 % to 90 % due to
radiation and the remainder is by convection.
An example piping and instrumentation diagram for a vessel testing facility is shown in Annex A. Test
equipment employed in the conduct of the test consists essentially of the following:
a) a specially designed burner arrangement to subject the test specimen to the conditions specified in
the calibration section;
b) propane storage capable of fuelling the test for the required duration;
c) equipment to control and monitor the propane flow rate throughout the test;
d) equipment to vent and purge the vessel after testing.
6.2 Burner arrangement
This test procedure uses liquid propane fuelled burners to simulate a pool fire. Burners are used
because they provide more control over the test conditions. The burner system shall be designed to
produce a low momentum and luminous fire of sufficient thickness so that the resulting heat flux is
predominantly by radiation (i.e. radiation fraction greater than 75 %).
To simulate pool fire conditions a burner system shall be used. Burners shall be designed to achieve
total engulfment and uniformity of heating and shall be present on all four sides of the vessel. The
maximum nozzle spacing shall be no greater than 0,5 m.
The burner design can be varied by the test laboratory to meet the calibration requirements; for
informative purposes, an example of burner design is shown in Annex A.
The burner arrangement shall be designed to receive equal mass flow rates of propane to two
diametrically opposite locations at the ends of the vessel to ensure broadly symmetrical heating.
The supply line length and fittings shall also be designed to ensure equal propane flow to the burner
arrangement and all supply lines. Cooling of the supply shall be provided as necessary to protect the
burner supply for the duration of the test. The burner system shall be designed to ensure stabilization of
the flow rate and stabilization of the flame temperatures (as defined by directional flame thermometers
(DFTs) in Clause 9 and Annex B) shall be achieved within 2 min of the test commencing.
6.3 Fuel supply for burners
The burner system fuel shall be commercial propane or LPG. The fuel supply shall be capable of
delivering up to 1,0 kg/s to the burner arrangement and controlling the flow rate to within ±0,05 kg/s
of the target flow rate as determined by calibration testing.
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ISO 21843:2018(E)

6.4 Test fluids
The test fluid for the test vessel shall be commercial propane or LPG. Means of filling the test vessel
(including air purge) prior to a test, and purging the vessel subsequent to the test to allow safe
inspection, shall be provided. Equipment to pump or push liquid propane from the test vessel back to
a storage vessel after the test may be utilised. A means of determining the total propane loss from the
test vessel throughout the test shall be available.
6.5 Test building
Large-scale exterior fire tests are subject to environmentally induced variations due to wind. Stricter
tolerances in deviation from the as-tested environmental conditions are imposed for testing if the test
is not protected from the environment through the use of an enclosure in the form of a shed or building.
These tolerances are described in 7.7
If used, environmental protection shall be suitably enclosed on all four sides and have full roof coverage.
Openings for ventilation shall be equally distributed and sized, so far as is practicable.
7 Calibration tests
7.1 General requirements
Due to the variations involved in external large-scale testing, it is required to successfully perform
three calibration tests before a particular fire burner system and test configuration is considered
suitable as the basis for fire testing.
The net heat flux to a water-filled vessel shall be determined and DFTs shall be used to assess both
the uniformity of heating and the radiation-convection balance. A thermal imager shall also be used to
confirm uniformity of heating and radiation-convection balance in the calibration tests. See Annex D for
methods to estimate the radiation-convection balance. All three tests shall be performed in accordance
with 7.2 and 7.3 and shall use the same vessel, burner configurations and test parameters.
The calibration test results shall be assessed in accordance with 7.4. Once a test configuration has
met the requirements in 7.5, it shall be considered suitable for testing of actual test specimens in
environmental conditions as defined in 7.6. The tolerances in variation from the calibration test set up
during actual fire testing are given in 7.7.
Calibration testing should be repeated in the event of any modifications to the test specimen beyond
the permitted tolerances in 7.7, any modifications to the burner or nozzle arrangement or propane flow
rate, any significant modifications to the test equipment or test building, or any departure from the
environmental conditions as defined in 7.6.
Calibration tests shall be performed at least every three years even in the event of no changes as
listed above, to ensure equipment functions as intended. Calibration test results shall be written
up as calibration reports as described in 7.8 and retained by the test laboratory for reference when
conducting future fire tests.
7.2 Calibration test vessel construction
The calibration vessel shall be manufactured according to appropriate pressure vessel regulations. It
shall have a minimum diameter of 1 200 mm, and a minimum length of 2 000 mm. The vessel shall be
supported on two steel saddles, which shall be insulated or water-cooled. No fire protection materials
or system shall be installed on the calibration vessel shell.
An appropriately sized vent shall be cut at the top of the vessel to permit extraction of thermocouples
and to prevent pressurization during calibration. An agitator shall be installed within the vessel,
located close to the middle. Only connecting piping required for operation of the agitator is permitted,
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ISO 21843:2018(E)

and this piping may be water-cooled if necessary. Any covers or guards for gauges and connections
shall be removed, and all remaining connections shall be sealed.
The vessel shell shall be instrumented with 16 DFTs. A simple design of DFTs is given as an example in
Annex B. DFTs shall be attached to the vessel in locations shown in Figure 1. Individual TCs that conflict
with the position of lifting lugs or fittings may be moved by up to 0,15 m. Thermocouples that conflict
with saddles shall be moved horizontally towards the middle of the vessel until they are at least 0,25 m
from the saddle.
The calibration vessel shall be internally instrumented with 10 insulated type k thermocouples (1,5 mm
minimum diameter) for measurement of the water temperature. The internal thermocouples shall
be located at two statio
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