Siemens FDOOT241-9 Technical Manual page 41

Building Technologies
Fire Safety & Security Products
Deceptive phenomena
Deceptive phenomena can deceive a fire detector and bring about a false alarm.
Depending on the fire detector in question, the deceptive phenomena may be e.g.
vapor, cigarette smoke, dust, dry ice in discotheques, exhaust fumes, aerosols
occurring during welding or heat sources such as radiant heaters or hot engines.
In a small hotel room with a rather low ceiling where vapor from the bathroom may
penetrate the room, or in operating facilities where a lot of dust is generated, many
deceptive phenomena must be taken into consideration. In a clean room where
electronic modules are fabricated the risk of deceptive phenomena is rather low.
Risk of fire
In production facilities where highly combustible materials such as flammable
liquids, cotton, paper etc. are processed and where electrical machines are
operated, the fire risk is very high. Minor overheating or sparks may cause a fire. In
a storehouse where steel is stored and where no electrical installation is provided
with the exception of lighting, the fire risk is very low.
Critical fire size
When a waste paper basket in a metal-processing facility catches fire, the
consequential damage is usually rather low. Here we are talking about a critical,
medium fire size that can still be tolerated. The situation is completely different in
pharmaceutical production facilities where even the lowest smoke concentration
may impair the process and where combustible materials are processed. Even the
smallest fire must be detected immediately. In this case, we speak of a small
admissible critical fire size.
Project engineering
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16.04.2009