2 cissp ® Official Study Guide Eighth Edition

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 acti-
vation 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 interven-
tion 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.

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Implement Site and Facility Security Controls 
421
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 systems. However, 
gas discharge systems should not be used in environments in which people are located. Gas 
discharge systems usually remove the oxygen from the air, thus making them hazardous to 
personnel. They employ a pressurized gaseous suppression medium, such as CO
2
, halon, or 
FM-200 (a halon replacement). 
Halon is an effective fi re suppression compound (it starves a fi re of oxygen by disrupting 
the chemical reaction between oxygen and combustible materials), but it degrades into toxic 
gases at 900 degrees Fahrenheit. Also, it is not environmentally friendly (it is an ozone-
depleting substance). In 1994, the EPA banned the manufacture of halon in the United 
States. It is also illegal to import halon manufactured after 1994. (Production of halon 
1301, halon 1211, and halon 2403 ceased in developed countries on December 31, 2003.) 
However, according to the Montreal Protocol, you can obtain halon by contacting a halon 
recycling facility. The EPA seeks to exhaust existing stocks of halon to take this substance 
out of circulation. 
Owing to issues with halon, it is often replaced by a more ecologically friendly and less 
toxic medium. The following list itemizes various EPA-approved substitutes for halon (see 
http://www.epa.gov/ozone/snap/fire/halonreps.html
for more information): 
■
FM-200 (HFC-227ea) 
■
CEA-410 or CEA-308 
■
NAF-S-III (HCFC Blend A) 
■
FE-13 (HCFC-23) 
■
Argon (IG55) or Argonite (IG01) 
■
Inergen (IG541) 
■
Aero-K (microscopic potassium compounds in aerosol form)
You can also replace halon substitutes with low-pressure water mists, but such systems 
are usually not employed in computer rooms or electrical equipment storage facilities. A 
low-pressure water mist is a vapor cloud used to quickly reduce the temperature in an area.