Siemens FDOOT221 Technical Manual page 50

4 Planning
Ambient features
50
Building Technologies
Fire Safety
Deceptive phenomena
Deceptive phenomena can deceive a fire detector and bring about a false alarm.
The deceptive phenomena differ depending on the fire detector. Examples of
deceptive phenomena include steam, cigarette smoke, dust, dry ice in
discotheques, exhaust fumes, aerosols occurring during welding, and 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 risk of fire 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 risk of fire 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. Therefore, we need to define what is
termed a small admissible critical fire size.
007004_n_en_--
01.07.2012