ISO 7240-7:2011 pdf free download – Fire detection and alarm systems一 Part 7: Point-type smoke detectors using scattered light, transmitted light or ionization.
5.18.2.3 Mounting of specimens
Mount the four specimens (Nos. 17, 18, 19 and 20) on the fire test room ceiling in the designated area (see Annex F) in accordance with the manufacturer’s instructions, such that they are in the least sensitive orientation relative to an assumed air flow from the centre of the room to the specimen.
Connect each specimen to its supply and monitoring equipment, as specified in 5.1.2, and allow it to stabilize in its quiescent condition before the start of each test fire.
Detectors that dynamically modify their sensitivity in response to varying ambient conditions can require special reset procedures and/or stabilization times. The manufacturer’s guidance should be sought in such cases to ensure that the state of the detectors at the start of each test is representative of their normal quiescent state.
5.18.2.4 Initial conditions
IMPORTANT — The stability of the air and temperature affects the smoke flow within the room. This is particularly important for the test fires that produce low thermal lift for the smoke (e.g. TF2 and TF3). Therefore, the difference between the temperature near the floor and the ceiling should be < 2 °C, and local heat sources that can cause convection currents (e.g. lights and heaters) should be avoided. If it is necessary for people to be in the room at the beginning of a test fire, they should leave as soon as possible, taking care to produce the minimum disturbance to the air. Before each test fire, ventilate the room with clean air until it is free from smoke, so that the conditions given below can be obtained. Switch off the ventilation system and close all doors, windows and other openings. Then allow the air in the room to stabilize and the following conditions to be obtained before the test is started: Diametrically opposite the hammer shaft are two steel counter-balance arms, each 20 mm in outside diameter and 185 mm long. These arms are screwed into the boss so that a length of 150 mm protrudes. A steel counterbalance weight is mounted on the arms so that its position can be adjusted to balance the weight of the striker and arms, as in Figure El. On the end of the central boss is mounted a 150 mm diameter aluminium alloy pulley, 12 mm wide, and around this is wound an inextensible cable, with one end fixed to the pulley. The other end of the cable supports the operating weight. The rigid frame also supports the mounting board on which the specimen is mounted by its normal fixings. The mounting board is adjustable vertically so that the upper half of the impact face of the hammer strikes the specimen when the hammer is moving horizontally, as shown in Figure E.1. To operate the apparatus, the position of the mounting board with the specimen is first adjusted as shown in Figure E.1 and the mounting board is then secured rigidly to the frame. The hammer assembly is then balanced carefully by adjustment of the counter-balance weight with the operating weight removed. The hammer arm is then drawn back to the horizontal position ready for release and the operating weight is reinstated. On release of the assembly, the operating weight spins the hammer and arm through an angle of 3ir12 rad to strike the specimen. The mass, in kilograms, of the operating weight to produce the required impact energy of 1,9 J equals 0,3881 kg, where r is the effective radius of the pulley, in metres. This equals approximately 0,55 kg for a pulley radius of 75 mm.