BS EN 50399:2011 pdf download – Common test methods for cables under fire conditions — Heat release and smoke production measurement on cables during flame spread test — Test apparatus, procedures, results
4.2 Air input
Air shall be introduced to the test chamber through a plenum box fitted directly underneath, and of approximately the same dimensions as, the air inlet aperture. The depth of the plenum box shall be (150 ± 10) mm. Air shall be blown into the plenum box from a fan through a rectangular straight section of duct of constant cross section of (300 ± 10) mm width and (80 ± 5) mm height and a minimum length of 800 mm, which shall enter from the rear of the chamber and be parallel to the floor and along the burner centre line as shown in Figure 1. The duct shall be arranged to inlet air to the plenum box through an aperture in the longest side, centred horizontally and such that the bottom of the duct shall be no greater than 10 mm above the bottom of the plenum box. A grid shall be fitted in the air inlet aperture to achieve uniform flow of the air. The grid shall be constructed of steel plate approximately 2 mm thick with holes of approximately 5 mm diameter drilled at approximately 8 mm spacing between centres. The airflow rate shall be measured in a circular duct prior to the rectangular cross section duct.
It shall be measured by a gas flow measuring device located at a straight section of the circular duct. The minimum length of straight circular section before and after the measuring device shall be selected according to the technical specification of the measuring device.
NOTE 1 A fluid flow measuring system according to either EN ISO 5167-2 (orifice plate) or EN ISO 5167-4 (Venturi tube) is recommended. Alternatively, a Pitot tube taking multiple samples across the section of the duct and averaging to account for variations across the section or a hot wire anemometer measuring at multiple positions across the section of the duct as described in Annex D may be used. The airflow shall be set prior to a test at (8 000 ± 400) l / min and shall not be changed during the test. The airflow shall be checked throughout the test and shall not vary by more than 10 % of the set value. NOTE 2 This information does not need to be recorded.
4.3 Hood A hood (see Figure 2) having a truncated shape, and where the base has a minimum length of 1,50 m and a minimum width of 1,00 m, shall be centred above the outlet of the test chamber. The base of the hood shall be raised above the top of the test chamber, with the largest side of the hood parallel to the largest side of the outlet of the chamber. NOTE 1 A gap of approximately 200 mm to 400 mm between the top of the test chamber and the base of the hood has generally been found suitable.
There shall be a chamber above the hood to allow a connection to the exhaust duct.
NOTE 2 Plates/baffles may be installed in the hood to improve mixing of the air / effluents.
The system shall be designed to collect all the combustion products leaving the test chamber through the outlet during the test. There shall be no leakage of flames or smoke. The exhaust capacity shall be at least 1 m³/s at normal pressure and a temperature of 25 °C. The exhaust system design shall not be based on natural convection.
NOTE 3 In order to extract all gases and vapours, especially in the case of heavily burning cables, or cables which require to be specially extinguished and produce high volumes of gases and vapours, an exhaust system with a capacity of 1,5 m³/s is recommended.