PARTICLE-TRANSPORT IN SAMPLING LINES USED IN FIRE DETECTION SYSTEMS

For certain application areas in fire detection, air sampling systems are used which sample at different locations. The sampled air is trans ported to one fire detector. The aerosol coming from a starting fire, transported to at least one of the openings of the pipe system, is mod ified mainly because of non-representative sampling at the intake, par ticle losses in the pipe and dilution by sampled air from other openin gs. These changes of the aerosol during transport for a model system d esigned using design rules given by the manufacturer, are calculated. The main goal of this article is to give information regarding which p article size range a sampling is possible for, to impart a feeling abo ut problems which may occur. For very small particles (< 0.1 mu m) and especially for very large particles (> 5 mu m), the particle losses b ecome important. However, dilution is the most important factor. The r eduction in concentration by using a multiple sampling system can be c ounteracted if the alarm level of the defector is reduced correspondin gly. In order to guarantee the same detection level, the alarm level f or the investigated model system has to be reduced to less than 1.8% o f the alarm level without a sampling pipe system. (C) 1997 Published b y Elsevier Science Ltd.