Peculiarities of Placement of Fire Detectors in Premises with Engineering Structures Located in the Ceiling Area

The placement of fire detectors in conditions of a protected facility significantly affects the efficiency of the detection of fire factors by fire detectors. Problems of the placement of point-type smoke, heat, and gas fire detectors in premises with engineering structures in the ceiling area located at a certain distance from the ceiling have been considered. The combustion source generates a convection column that carries fire factors (heat, smoke, and gaseous combustion products), usually with an opening angle of about 15°. Having reached the ceiling, the airflow generated by the convection column starts spreading horizontally in all directions. The horizontal component of the rate of propagation of fire factors depends on the intensity of a combustion source and the distance from the fire source axis. The process of the spread of fire factors in the ceiling area changes in case of beams, ventilation ducts, and other engineering and technological structures located on the ceiling that protrude from a partition and prevent the spread of fire factors. It is common that a gap remains between the partition and the upper part of engineering structures, i.e., the engineering structure is not installed directly to the ceiling but at some distance from it. In this case, the main parameters affecting the distribution of fire factors are the height of the gap, the width of the engineering structure, and the horizontal air mass velocity generated by the airflow from the fire source and depending on the intensity of the combustion source. In case of a slowly developing smoldering characterized by the low velocity of airflows, fire factors may not bypass the gap between the engineering structure and the partition, whereas in the case of intensive combustion accompanied by active movement of air masses, the heat, smoke, and gaseous combustion products will pass the gap freely. The experiments have used five types of point-type smoke fire detectors. The following test fire sources have been used as a combustion load: TF-2A (pyrolysis smoldering of wood) and TF-5 (combustion of a flammable liquid with smoke emission). The test fire source TF-2A generates a lower air mass velocity when compared with the TF-5 source. A 500 mm wide box simulator has been used as an engineering structure. The first test has been conducted without the box in the ceiling area. Then, the box simulator has been alternatively installed in the ceiling area, creating a gap between the partition and the upper plane of the box of 50, 100, and 200 mm. The test fire source has been placed from one side of the box simulator’s projection to the floor, whereas fire detectors have been installed in the ceiling on the other side of the box simulator. During the tests, the activation time of fire detectors has been controlled. The test results confirm the theoretical conclusions.