Description of BS 476-24:1987 2014

1.1 This International Standard 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 This International Standard is not applicable to:

1. 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.

2. 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 This International Standard is not appropriate for the following ducts unless the further criteria described in the an­ nex are established to the satisfaction of the appropriate authority:

1. 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.

2. smoke outlet ducts;

   NOTE – These ducts need to retain their integrity and cross­ sectional area under fire conditions. Consequently criteria for ac­ ceptance additional to those given in this International Standard are required. This International Standard is only applicable, therefore, to smoke outlet ducts if the criteria for integrity failure of a representative smoke outlet duct within the furnace and the loss of retention of cross-sectional area of such ducts are agreed between all parties concerned and are investigated and reported (see the annex).

3. ducts lined on the inside with combustible material or which in practice may accumulate combustible deposits on their inside face (such as kitchen extract ducts).

   NOTE – Additional criteria regarding the insulation performance of the duct are required in this case (see the annex).

1.6 This International Standard does not take into consideration the effect of impact shock loading on ducts due to the collapse of supporting or adjacent structural members or other components, or of impact- or thermal shock loading resulting from the application of a water (hose) stream.

NOTE – The method described in this International Standard should be used solely to measure and describe the properties of ducts and their supports in response to heat and flame under controlled laboratory conditions and should not by itself be considered or used for the description. appraisal or regulation of the fire hazard of such ducts or supports under actual fire conditions.

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