User Manual

e1851a

Siemens Building Technologies

Cerberus Division

01.2002

Fire aerosols versus

airflow

Fire aerosols which arise in a clean room are comparable

with airborne foreign particles. Depending on the size and

type of fire, they are diluted by the powerful air flow and im-

mediately swept away

Detectors on the ceiling Conventional fire detection systems with detectors on the

ceiling are only suitable for the early detection of incipient

fires in clean rooms in areas of non-unidirectional airflow

with 10 – 50 changes of air/h. (service areas)

When using point-type smoke detectors, they must be in-

stalled according to the EDP system monitoring concept

with 25m

per detector and a distance of 5m between de-

tectors. The area of a perforated ceiling around the detec-

tor must be sealed according to CRP e432.

In areas with unidirectional airflow (laminar flow) ceiling-

mounted detectors provide redundant protection against a

catastrophe.

Air handling equipment The treated outside air and circulated air must always be

monitored after the air handling equipment by air sampling

smoke detector units type DBZ1197/DO1153.

This enables fires in the air handling equipment as well as

smoke drawn in with the outside air to be detected at an

early stage.

Pressure differences

between adjacent

workrooms

Another tricky point is the pressure differences between

adjacent workrooms. With the air sampling smoke detec-

tion system, where the air is extracted via a tube system,

after the active detector the air extracted must be taken

back to the area with the same air pressure.

For the planning of a fire detection system in a clean room, it is essential that the air han-

dling system concept is known. The planning engineer must be familiar with the various air

handling concepts and design the fire detection system accordingly.

3.3 Typical fire hazards

D the ignition of process gases and solvents in heating equipment

D short circuit/overloading in equipment and installations

D danger through fires from outside

D arson/tampering