ISO 23693-3:2026

International
Standard
ISO 23693-3
First edition
Determination of the resistance
2026-06
to gas explosions of passive fire
protection materials —
Part 3:
Tubular and I-section substrates
subject to elastic deformation only
Détermination de la résistance aux explosions de gaz des
matériaux de protection passive contre l’incendie —
Partie 3: Supports tubulaires et de section en I soumis à une
déformation élastique uniquement
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Explosion loads . 2
5 Test methods . 3
5.1 General .3
5.2 Method 1: measuring stagnation pressure and side-on overpressure .4
5.2.1 Testing with an instrumented tubular .4
5.2.2 Testing without an instrumented tubular .4
5.2.3 Measuring side-on overpressure .6
5.3 Method 2: use of computation fluid dynamics (CFD) modelling .7
6 Test specimens . 8
6.1 General .8
6.2 Other section types .8
7 Environmental conditions . 9
8 Instrumentation . 9
9 Test specification . 9
10 Data analysis . 9
11 Test acceptability criteria .11
11.1 Test method 1 .11
11.2 Test method 2 .11
12 Test report .11
Annex A (informative) Measurement of side-on overpressure .12
Annex B (normative) Description of damage to PFP .15
Bibliography . 17

iii
Foreword
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iv
International Standard ISO 23693-3:2026(en)
Determination of the resistance to gas explosions of passive
fire protection materials —
Part 3:
Tubular and I-section substrates subject to elastic
deformation only
1 Scope
This document describes methods for simulating the mechanical loads that can be imparted to passive fire
protection (PFP) materials and systems by explosions resulting from releases of flammable gas, pressurized
liquefied gas, flashing liquid fuels, or dust that can precede a fire.
These methods can be used to determine the resistance of passive fire protection materials to such events.
This document considers PFP materials applied to substrates that are subject to the combined effects of
pressure and drag that occur in the flow path of an explosion. This document excludes specimens in which
the substrate is subject to plastic deformation or brittle failure
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 23693-1, Determination of the resistance to gas explosions of passive fire protection materials — Part 1:
General requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
congested region
region that is occupied by items that provide obstacles to flow ahead of the flame,
thereby increasing flame velocity, the rate at which energy is released, and the overpressure produced
3.2
drag load
load on items resulting from the flow of gas generated by a gas explosion
3.3
overpressure
difference between actual pressure and ambient pressure

3.4
pressure load
load on an object resulting from the overpressure (3.3) generated by a gas explosion
3.5
projected area
part of the vent area that the instrumented test specimen covers
3.6
rise time
time for the pressure in a blast wave to rise to the peak overpressure (3.3)
3.7
side-on overpressure
overpressure (3.3) measured at right angles to the direction of travel of a blast wave
Note 1 to entry: This can also be described as incident or free field overpressure.
3.8
stagnation pressure
pressure at a location perpendicular to and facing the direction of the flow, where the velocity of the
explosion gases has been reduced to zero
3.9
streamlined housing
housing that a pressure transducer can be mounted into, which, if aligned with the direction of travel of the
blast wave and flow generated by a gas explosion, allows the side-on overpressure (3.7) to be measured
3.10
substrate
section to which the passive fire protection (PFP) materials are attached or mounted
4 Explosion loads
Methods for generating explosive loads are described in ISO 23693-1. Due to the nature of the specimen
being tested, it will be exposed to a combination of overpressure and drag loads. Pressure loads come from
the overpressure generated by the explosion; the drag loads are generated by the high velocity gas flow
around the object. To ensure that PFP systems applied to this type of object can survive a gas explosion it is
necessary to test them against a combination of pressure and drag loads.
To achieve a combination of pressure and drag loads, the test specimen shall be located in, or near, the vent
of a confined gas explosion or at the edge of the congested region of an unconfined gas explosion, where the
velocity of the gas flow will produce a drag load.
The pressure load is obtained by measuring the side-on overpressure.
Drag load is characterized either by measuring the stagnation pressure on an instrumented tubular
positioned so as to receive the same drag load as the specimen being tested or by instrumenting the
specimen being tested. When the instrumented tubular is used, it shall be located in the same position as the
specimen during a calibration test conducted under the same test conditions.

The drag load on an object in a flow is given by Formula (1):
D = C A p (1)
L D dyn
where
D is the drag load, in newtons (N);
L
C is the drag coefficient of object;
D
A is the projected area of object normal to flow direction, in square metres (m );
p is the dynamic pressure, in newtons per square metre (N/m ), and is calculated using
dyn
Formula (2):
p = ρu /2 (2)
dyn
where
ρ is the gas density, in kilograms per cubic metre (kg/m );
u is the flow velocity, in metres per second (m/s).
It is difficult to know the actual drag coefficient of an object as it changes with shape, orientation, flow
velocity and flow conditions. When computer programs that model the effects of a gas explosion calculate
drag load they typically assume a C of unity, so drag load is equal to the dynamic pressure.
D
When conducting gas explosion trials, the dynamic pressure can be calculated from the measured stagnation
pressure and side-on pressure using Formula (3):
p = p – p (3)
dyn stag side
where
p is the stagnation pressure, in newtons per square metre, (N/m );
stag
p side-on pressure, in newtons per square metre, (N/m ).
side
NOTE 1 The actual drag load on an object is dependent both on the flow velocity and the drag coefficient of the
object. The drag coefficient is dependent on the geometry and orientation of the object being considered.
NOTE 2 This document does not consider bending or deflection of samples. If used for rating PFP performance of
bending and deflection, it is necessary to perform additional analysis.
Test laboratories should be aware of the significant potential hazards involved in gas explosion resistance
testing and take appropriate steps to ensure the safety of all concerned.
5 Test methods
5.1 General
Two test methods are available, both designed to ensure that the required levels of overpressure and drag
load are attained. The two methods are:
a) Method 1: quantifying the drag and pressure loads by direct measurement of the stagnation pressure
and side-on overpressure.
b) Method 2: using computational fluid dynamic modelling to simulate the gas explosion such that the drag
load and overpressure load on the specimen under test can be calculated.
These methods are described in 5.2 and 5.3.

5.2 Method 1: measuring stagnation pressure and side-on overpressure
5.2.1 Testing with an instrumented tubular
An instrumented tubular shall have a minimum external diameter of 100 mm. Its external diameter shall
be within ±20 % of the tubular diameter or I-beam depth of the specimen to be tested. For testing involving
an I-beam section, the depth of the section is the dimension of the specimen measured perpendicular to
the flow direction and perpendicular to the span. The instrumented tubular shall have three pressure
gauges mounted to measure the stagnation pressure of the flow, see Figure 1. The pressure gauges shall
be mounted in the central 50 % of the length of the tubular spaced 100 mm apart (see Figures 1 and 2). If
multiple specimens are to be tested then the same number of instrumented tubulars shall be required in a
calibration test and put in the same positions in which the specimens are to be mounted. When a calibration
test has been carried out using an instrumented tubular(s) the result of the test will be considered valid for
any specimen tested to the same test conditions. The calibration would only need to be repeated if there is
a change in the test conditions.
NOTE I-beam refers to I sections of any dimension.
5.2.2 Testing without an instrumented tubular
If an instrumented tubular is not used then the specimen(s) being tested shall be instrumented to measure
stagnation pressure. This shall be done without impairing the PFP systems being tested. If the test specimen
is a tubular, the three pressure gauges shall be mounted as shown in Figures 1 and 2. If the specimen to be
instrumented is an I-beam then three pressure gauges are to be mounted on it as shown in Figures 3 or 4
depending on the orientation of the I-beam relative to the flow path.
Dimensions in millimetres
Key
p stagnation pressure transducer
stag
1 direction of gas flow
Figure 1 — Pressure gauge layout on an instrumented tubular

Key
1 instrumented tubular or specimen
2 region in which pressure gauges can be located
3 supports
L length of instrumented tubular or specimen
Figure 2 — Region in which pressure gauges can be located on instrumented tubular or I-beam
specimens
Dimensions in millimetres
Key
Y section
d section depth
1 direction of gas flow
Figure 3 — Pressure gauge layout on an instrumented I-beam – Flow impacting on web

Dimensions in millimetres
Key
Z section
d section depth
1 direction of gas flow
Figure 4 — Pressure gauge layout on an instrumented I-beam – Flow impacting on flange
5.2.3 Measuring side-on overpressure
Side-on overpressure shall
...