BS 476-24:1987 download free.Fire tests on building materials and structures Part 24: Method for determination of the fire resistance of ventilation ducts — [ISO title: Fire resistance tests — Ventilation ducts].
0 Introduction
BS 476-24 has been prepared because a fire resistance test for ventilation ducts has become necessary in order to permit evaluation of ducts designed to prevent fire spread across fire barriers in the absence of fire dampers. It should be read in conjunction with ISO 834.
The Annex provides explanatory notes which give important background information, but it does not constitute a mandatory part of this International Standard.
SAFETY WARNING — So that suitable precautions may be taken to safeguard health, the attention of all concerned in fire tests is drawn to the possibility that toxic or harmful gases may be evolved during the combustion of test specimens.
1 Scope and field of application
1.1 BS 476-24 specifies a method of test and criteria for the determination of the fire resistance of vertical and horizontal ventilation ducts under standardized fire conditions.
1.2 The general purpose of this test is to measure the ability of a representative duct or duct assembly to resist the spread of fire from one fire compartment to another without the aid of fire dampers.
1.3 It is applicable to vertical and horizontal ducts, with or without branches, taking into account joints, air supply and exhaust openings, as well as suspension devices, etc.
1.4 BS 476-24 is not applicable to:
a) ducts above fire-resisting suspended ceilings (horizontal membranes) in those cases where the ducts rely for their fire resistance on the performance of the ceiling;
NOTE Other tests are necessary for these ducts,
b) ducts containing fire dampers at points where they pass through fire separations.
NOTE In order to assess the fire resistance of fire dampers. other tests are required. A method of test for fire dampers is under consideration as a subject for a future International Standard.
1.5 BS 476-24 is not appropriate for the following ducts unless the further criteria described in the Annexare established to the satisfaction of the appropriate authority:
a) ducts of materials which are extremely sensitive to thermal shock;
NOTE Thermal shock may affect such ducts in a way that would differ from the effect in this test, but the test may still be used where it can be established that sensitivity to thermal shock is within acceptable limits.
c) restraint forces at the penetration point in the furnace wall opposing horizontal expansion of the ducts, to provide an indication of potential
structural failure of lightweight partitions
through which the ducts may pass; however, if the duct specimen at the penetration point is
fire-stopped with mineral wool or other flexible fire-stopping, there will not be any full restraint at this point (see 7.2.9 and the Annex), and if the duct is restrained outside the furnace (see 7.2.9), it will not be appropriate to measure restraint
forces at the penetration point.
3.4 The test takes into account the effect of fire
exposure from the outside as well as the effect of fire entering the ducts in conditions where forced air
movement may or may not be present.
3.5 The test specimens incorporate the usual joints and exhaust openings and are suspended as they
would be in practice. The specimens are supplied with air in a manner which is indicative of the
“fan off’ and “fan on” situations which could arise in practice.
As the load-bearing capacity of suspension or fixing devices is often critical in a fire, additional separate evaluation of these devices is required. This evaluation may be carried out in a separate furnace. For the suspension and fixing devices, the
evaluation procedure may be separated into parts, such as tests for the device for fastening to the floor, ceiling or wall, tests for the device for fastening to the duct and tests for the hangers. After having
chosen the correct fastening device and hanger, the complete assembly can be evaluated.
3.6 If specified by the sponsor, part of the test may be omitted if the duct concerned is not required, in practice, to meet all the conditions envisaged by the test: for example a duct designed for use only in the vertical position need not be tested in the horizontal position. Any such deviations from the full test
procedure shall be clearly described in the test report.
4 Apparatus
The main items of apparatus are as follows:
4.1 Furnace, capable of subjecting a ventilation duct to the standard heating and pressure conditions
specified in clause 5, suitable for testing ducts in the vertical (see Figure 1) or horizontal (see Figure 2)
position.
4.2 Device, if applicable (see 3.3), fixed to the furnace wall, for measuring the forces which
restrain thermal elongation in horizontal ducts. A test arrangement for this purpose is shown in Figure 3. Details are described in the Annex.
The positions of the thermocouples shall be as shown in Figure 6 and Figure 71) Thermocouples for estimating average temperature shall be placed in such a way as to give information representative of the normal heat transfer through the walls of the ducts.
5.1.5 Measurement of temperatures of flue gases
The gas temperatures inside the ducts shall be measured at the locations shown in Figure 6 and Figure 7. The hot junctions of the thermocouples shall be placed centrally in the ducts and at the centre of the top edge of the opening in the vertical duct A (see Figure 6). Further details are given in ISO 834, subclause 4.1.2.3.
5.2 Pressure conditions
The furnace pressure shall be maintained according to ISO 834, subclause 4.2.
The neutral plane shall be below the horizontal specimen. The pressure inside horizontal duct A (see Figure 2) shall be 300 ± 10 Pa below the ambient (laboratory) pressure at the beginning of the test, and during the test the fan setting shall not be altered. The underpressure shall be continuously recorded to provide a measure of air leakage.
5.3 Air velocity
The air velocity in duct B (see Figure 1 and Figure 2) shall be 3 mIs measured at ambient temperature at the start of the test and thereafter the fan velocity shall not be readjusted. The measuring point shall be located inside the tube connecting the test specimen to the fan. The measurements shall then be corrected by the ratio of the cross-sectional areas.
6 Preparation of test specimens
6.1 Dimensions
6.1.1 The test specimens shall normally be full size.
6.1.2 If compliance with the requirements of 6.1.1 is not possible, the following shall be the minimum dimensions of the parts of test specimen exposed:
a) in the furnace (see Figure 1 and Figure 2 and
clause A.5):
1) horizontal ducts: length 3,0 m,
2) vertical ducts: length 2,0 m;
b) outside the furnace:
1) horizontal ducts: length 2,5 m,
2) vertical ducts: length 2,0 m.