FIRE PROTECTION SYSTEMS
Halon systems often protect data processing centers and other areas which
contain sensitive electrical equipment. Such systems also exist in electric
and telephone switchgear rooms. In addition to the type of hazard
protected, another critical criterion for using halon is the need to provide a
tight enclosure. Since halon is a gas, it can leak through improperly sealed
openings and, as a result, the required design density is not maintained.
Lately, there has been great concern over the effects halon has on the
environment, and in particular its depletion effect on the ozone layer. This
has resulted in a re-evaluation of the use of halon as a fire suppression
agent. In addition, the use of halon in acceptance testing has been subject
to study, and options such as using different test gases (e.g., sulfur
hexafluoride, SF
6
) are now being evaluated. Several new products are
now under development to replace the halon agent in existing fire
suppression systems.
Dry Chemical
Dry chemical extinguishing agents can extinguish extremely fast if
introduced directly into the flaming area. Smothering and cooling result
from the application of dry chemical agents, but the primary extinguishing
capabilities result from the combustion-chain-reaction-breaking abilities of
the dry chemical agent. This is the same principal extinguishing feature of
halons.
Dry chemical fire suppression systems use a dry chemical powder mixture
as an extinguishing agent. Common dry chemical agents include sodium
bicarbonate, potassium bicarbonate, urea-potassium bicarbonate, and
monoammonium phosphate. Additives in the base compound reduce
caking, promote water repellence, and increase flow and storage
characteristics. Examples of common additives include metallic stearates,
tricalcium phosphates, and silicones. Multipurpose dry chemical usually
refers to the monoammonium agent which can be used to suppress fires
involving ordinary combustibles, and energized electrical equipment as
well as flammable liquids.
Regular dry chemical is not considered a good agent for ordinary
combustibles, since water also must be applied to attack any subsurface
burning which the regular dry chemical cannot reach. The multipurpose
agent does have penetrating abilities, thus its multipurpose listing. Agents
should never be mixed unless specifically listed for mixing, as some
agents will generate CO
2
.
This may cause containers to explode and the
agent to cake.
SM PS-24