New York City Dry Chemical Fire Extinguishers
The most
common household fire extinguisher is the dry chemical extinguisher. The dry
chemical extinguisher is designed to handle Class A fires such as organic solid
material such as wood, Class B fires that involve liquid such as gas and oil,
and Class C fires that involve electricity. The dry chemical extinguisher can
be designed and installed for fixed system use and portable extinguisher use.
If using a portable dry chemical extinguisher use caution when fighting active
fires and contact authorities should the fire breach the contained area.
Fire has a
long history of presenting issues to humankind through loss of life, loss of
property, and personal possessions. The first patented fire extinguisher was
created in 1723, by Ambrose Godfrey designed to extinguish a fire should the
need arise. Since then many improvements have been made and fire extinguishers
are now designed for specific use, such as the dry chemical fire extinguisher.
DRY
CHEMICAL EXTINGUISHING AGENTS
Wikipedia states there are several types of
dry chemical fire extinguishing agents that are listed below.
Dry
chemical This is a powder based agent that extinguishes by separating the four
parts of the fire tetrahedron. It prevents the chemical reaction involving
heat, fuel, and oxygen and halts the production of fire sustaining
"free-radicals", thus extinguishing the fire.
Mono ammonium phosphate, also known as "tri-class",
"multipurpose" or "ABC" dry chemical, used on class A, B,
and C fires. It receives its class A rating from the agent's ability to melt
and flow at 177 °C (350 °F) to smother the fire, more corrosive than other dry
chemical agents, pale yellow in color.
Sodium bicarbonate, "regular" or
"ordinary" used on class B and C fires, was the first of the dry
chemical agents developed. In the heat of a fire, it releases a cloud of carbon
dioxide that smothers the fire. That is the gas drives oxygen away from the
fire, thus stopping the chemical reaction. This agent is not generally
effective on class A fires because the agent is expended and the cloud of case
dissipates quickly, and if the fuel is still sufficiently hot, the fire starts
up again. While liquid and gas fires don't usually store much heat in their
fuel source, solid fires do. Sodium bicarbonate was very common in commercial
kitchens before the advent of wet chemical agents, but now is falling out of
favor, as it is much less effective than wet chemical agents for class K fires,
less effective than Purple-K for class B fires, and is ineffective on class A
fires, white or blue in color.
Potassium bicarbonate (aka Purple-K), used on class B and C
fires. About two times as effective on class B fires as sodium bicarbonate, it
is the preferred dry chemical agent of the oil and gas industry. The only dry
chemical agent certified for use in ARFF by the NFPA, Violet in color.
Potassium bicarbonate & Urea Complex (aka Monnex/ Powerex),
used on Class B and C fires. More effective than all other powders due to its
ability to decrepitate (where the powder breaks up into smaller particles) in
the flame zone creating a larger surface area for free radical inhibition. Grey
in color.
Potassium Chloride or Super-K dry chemical was developed in
an effort to create a high efficiency, protein-foam compatible dry chemical.
Developed in the 60s, prior to Purple-K, it was never as popular as other
agents since, being a salt, it was quite corrosive, for B and C fires, white in
color.
Foam-Compatible,
which is a sodium bicarbonate
(BC) based dry chemical, was developed for use with protein foams for fighting
class B fires. Most dry chemicals contain metal stearates to waterproof them,
but these will tend to destroy the foam blanket created by protein (animal)
based foams. Foam compatible type uses silicone as a waterproofing agent, which
does not harm foam. Effectiveness is identical to regular dry chemical, and it
is light green in color (some ANSUL brand formulations are blue). This agent is
generally no longer used since most modern dry chemicals are considered
compatible with synthetic foams such as AFFF.
MET-L-KYL / PYROKYL is a specialty variation of sodium
bicarbonate for fighting pyrophoric liquid fires (ignite on contact with air).
In addition to sodium bicarbonate, it also contains silica gel particles. The
sodium bicarbonate interrupts the chain reaction of the fuel and the silica
soaks up any unburned fuel, preventing contact with air. It is effective on
other class B fuels as well, blue, red in color.
OSHA
has the following requirements for commercial buildings and public use
facilities:
• Part Number: 1910
• Part Title: Occupational Safety and Health Standards
• Subpart: L
• Subpart Title: Fire Protection
• Standard Number: 1910.161
• Title: Fixed extinguishing systems, dry chemical.
--------------------------------------------------------------------------------
1910.161(a)
Scope and application
This section applies to all fixed
extinguishing systems, using dry chemical as the extinguishing agent, installed
to meet a particular OSHA standard. These systems shall also comply with
1910.160.
1910.161(b)
Specific requirements
1910.161(b) (1)
The employer shall assure that dry chemical agents are compatible with any
foams or wetting agents with which they are used.
1910.161(b) (2)
The employer may not mix together dry chemical extinguishing agents of
different compositions. The employer shall assure that dry chemical systems are
refilled with the chemical stated on the approval nameplate or an equivalent
compatible material.
1910.161(b) (3)
When dry chemical discharge may obscure vision, the employer shall provide a
pre-discharge employee alarm which complies with 1910.165 and which will give
employees time to safely exit from the discharge area prior to system
discharge.
..1910.161(b) (4)
1910.161(b) (4)
The employer shall sample the dry chemical supply of all but stored pressure
systems at least annually to assure that the dry chemical supply is free of
moisture which may cause the supply to cake or form lumps.
1910.161(b)(5)
The employer shall assure that the rate of application of dry chemicals is
such that the designed concentration of the system will be reached within 30
seconds of initial discharge.
[45 FR 60712, Sept. 12, 1980]
