Page 705 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

environments, whereas gaseous systems are more appropriate for
computer rooms where personnel typically do not reside.

Water Suppression Systems
There are four main types of water suppression systems:

A wet pipe system (also known as a closed head system) is always
full of water. Water discharges immediately when suppression is
triggered.

A dry pipe system contains compressed air. Once suppression is
triggered, the air escapes, opening a water valve that in turn causes
the pipes to fill and discharge water into the environment.

A deluge system is another form of dry pipe system that uses larger

pipes and therefore delivers a significantly larger volume of water.
Deluge systems are inappropriate for environments that contain
electronics and computers.

A preaction system is a combination dry pipe/wet pipe system. The
system exists as a dry pipe until the initial stages of a fire (smoke,
heat, and so on) are detected, and then the pipes are filled with
water. The water is released only after the sprinkler head activation

triggers are melted by sufficient heat. If the fire is quenched before
sprinklers are triggered, pipes can be manually emptied and reset.
This also allows manual intervention to stop the release of water
before sprinkler triggering occurs.

Preaction systems are the most appropriate water-based system for
environments that house both computers and humans together.

The most common cause of failure for a water-based system

is human error, such as turning off a water source when a fire
occurs or triggering water release when there is no fire.

Gas Discharge Systems

Gas discharge systems are usually more effective than water discharge