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ACE
FIRE PREVENTION LTD.
|
| Class
A |
For
use on fires involving common household items such as wood,
cloth, and paper |
|
Class
B |
For
use on fires Involving flammable liquids, plastics, solvents,
and gasses (includes fires listed as Class
K or E) |
Class
C |
For
use on fires Involving energized electrical
circuits such as distribution panels, transformers, appliances,
motors and the like |
NOTE: There are two additional FIRE classifications: Class D Fires - Involve combustible metals. Magnesium, phosphorus, sodium and powdered aluminum (the latter is used in solid fuel rockets) are the more common examples. Class D fires utilize chemically generated oxidents and cannot be extinguished by any means other than total fuel exhaustion (in other words you must allow it to burn itself out); Class K (also known as Class E) Fires - Involve cooking oils and fats. |
Water should never be used (in the limited quanties you would normally encounter in a bucket for instance) on a Class B or Class C fire. In the former you could risk spreading the burning fuel over a larger area while in the latter case you risk electrocution (both having very unpleasant results).
Which brings us to the perfect place to introduce another type of fire extinguishing "agent". Sand has been used to combat fires for almost as long as the bucket full of water. Old style fire engines had large buckets of sand hanging from them. Sand limits the amount of fuel available to a fire by reducing the area of contact with the air (oxygen). On a flammable liquid fire, it also has the benefit of absorbing the fuel and preventing it from spreading further. It does little to cool the fire though.
What
comprises the modern fire extinguisher, and how does it work?
We're going to answer this question and more
in the following paragraphs.
The fire extinguisher has several main parts, most obvious of which is the container (or bottle). It's usually constructed of spun aluminum or welded steel, is cylindrically shaped to make it easy to handle and store, is usually small enough for a single person to carry, hold or operate, and is simple enough for practically anyone to use. At the top of the cylinder is a valve assembly with an operating lever that's usually incorporated into the carry handle. A pin or other simple locking device prevents the operating lever from being inadvertently triggered during transport, inspection, or servicing. A gauge usually located adjacent to the handle of pressurized extinguishers informs the user that the unit is ready for use, has not been accidentally discharged, or isn't dangerously overcharged. Nitrogen is used to pressurize the cylinder to about 195 PSI and also serves as the propellant for the agent.
Fire extinguishers utilize several different types of agents designed to prevent the spread of, or extinguish, specific types of fires. A metal label affixed to the side of the cylinder will identify the type and amount of extinguishing agent it stores. The most commonly seen extinguisher is the pressurized five pound ABC. This unit uses a fine powder agent called sodium biphosphate. ABC extinguishers are rated for use on all types of fires, but they remain most effective on liquid or electrical fires. The powder inside the bottle is so fine that it actually interfers with the fire's ability to burn fuel (limits it's access to available oxygen). Because it doesn't cool the fuel however, it's not able to prevent it from "reflashing" but if sufficient powder is able to cover an area, the same effect as our plain old bucket of sand is achieved.
NOTE: An ABC extinguisher should not be used in a kitchen. The powder will adhere to hot surfaces and is not water soluble which makes it extremely difficult to clean up. In addition, the pressurized discharge of this type of extinguisher can result in the "scattering" of burning materials which might spread the fire to other areas. A better unit is the foam extinguisher. Water based foam extinguishers are most effective in that they cover a wide area, cool the fuel, and prevent reflash by preventing air from coming into contact with the fuel. Rated AB, you should use caution when using foam agents around live electrical equipment. |
There are several types of agents used in pressurized extinguishers that carry the BC label. Sodium bi-carbonate, potassium bi-carbonate (Purple K), carbon dioxide (CO2) and halogenated gas are common examples (although halon gas is being replaced by other less harmful-to-the-environment agents). The two powder agents in common use in BC rated extinguishers both have the same immediate quenching effect as the powder contained in the ABC extinguisher, with the added benefit of being easier to clean (as they're both water soluble). CO2 and halon type extinguishers are stored in liquid form inside the cylinder and discharge as a gas at room temperature. CO2 is heavier than air and will displace it while halon interfers directly with the combustion process. Both smother the fire by limiting its access to oxygen. Unfortunately both these agents can be lethal if used in enclosed spaces and you should use caution if you're exposed to them for long, as they limit your own body's ability to process oxygen. CO2 has the added benefit of cooling the immediate environment as it absorbs heat during a discharge. Water vapour present in the air will freeze instantly which is why discharging a CO2 extinguisher is often accompanied by dense "fog" and visible ice crystals.
NOTE: CO2 extinguishers are high pressure cylinders and do not use Nitrogen as a propellant. They do not have a gauge to indicate their state of readiness either, so it's very important to ensure the pin or locking mechanism that prevents inadvertent operation of the operating lever is "sealed" by the company (or individual) performing the routine service or recharging. CO2 extinguishers must be weighed regularily to ensure the unit complies with the manufacturer's stamped requirements. |
EXTINGUISHER FAQ
What
is a six year maintenance?
This
is a procedure where the extinguisher is actually discharged, the
interior of the cylinder is visually inspected, it's refilled with
powder and recharged. A permanent tag is affixed to the cylinder identifying
a successfully completed test.
What
is a hydro-test?
A
test that is performed every five years
in the case of a pressurized water or high pressure (CO2)
extinguisher, and every twelve years on most low pressure
dry chemical extinguishers. The extinguisher is emptied of all agent,
filled with water and pressurized to between five and six hundred
PSI (Pounds per Square
Inch). High pressure cylinders are subjected to a
2000 PSI test. During the course of the test, cylinder deformation is measured against the manufacturer's published tolerances as well as to ensure the welded
seams are intact. The test is designed to expose any weakness in the cylinder wall caused by negligent handling, improper maintenance, or hidden stresses.
The cylinder is then blown dry, refilled with fresh agent and recharged.
A special metal tag is permanently affixed to the side of the cylinder identifying
it as having successfully passed the hydro-test inspection (in the case of a CO2 extinguisher, the unit's neck is stamped with the date and registration number of the testing agency). All hydro-static testing MUST be performed by a registered Transport Canada Cylinder Re-certification Agency.
When
should I use a fire extinguisher?
To clear a path through
a fire (if you're trapped) or to control a small fire (keep it from
spreading to adjacent structure or other combustible material) until
the fire department arrives to ensure it's properly extinguished and
the fire won't reflash. To be safe, the fire department should be
called whenever a fire extinguisher is used to put out a fire.
I've
noticed the fire department routinely uses water even on a burning
car. Isn't this dangerous?
The
large quantity of water delivered through the typical fire hose will
extinguish (knock down in the jargon of most fire rescue personnel)
most car fires. The water cools the hot metal surfaces of the vehicle
and prevents it from re-igniting the combustible material. In all
car fires, the first thing the responding fire company will do is
cut the cables to the battery as well (to eliminate the addition of
an electrical fire into the "mix").
How
often do I have to have my fire extinguisher checked?
You
should be checking the extinguisher on a monthly basis at least. During
your monthly test, remove the extinguisher from the cabinet and (if it happens to be a dry-chemical extinguisher) turn
it upside down briefly. This ensures the powder remains loose and "fluffy". On
any vehicle mounted dry chemical units, turn the extinguisher upside down once
a week. Look for any dents or deep scratches on the cylinder. Ensure
the seal protecting the locking pin is in place (not broken or missing).
Check to make sure the pin isn't bent or damaged and that the nozzle is
clear and unobstructed. The indicator on the pressure gauge should be
somewhere in the green zone. If you notice any damage to the head, handle,
or operating lever, you should contact us to have the unit serviced.
What's
the purpose of the inspection tag?
This
ensures the unit has been checked by a qualifed techician (or an individual
that's been trained to perform an annual test of the apparatus). It
is your assurance that the unit will function when needed, has not
been physically damaged or partially discharged. Fire extinguishers
are weighed to ensure the proper amount of agent is present and ready
for use. This doesn't guarantee that the unit may have become damaged.
The monthly test (weekly on mobile mounted units) is designed to discover
that.
I
want to engrave my building's name on our extinguishers to help prevent
theft. Can I do this safely?
You
cannot engrave or use a punching tool to stamp letters onto a low pressure fire
extinguisher cylinder. Doing so will cause it to be rejected on the
next annual inspection. You are in fact weakening the cylinder wall
and this could cause it to fail at this point possibly injuring you
or anyone next to the unit when the failure occurs. You can engrave
the handle or the operating lever as long as you're careful not to
deform it which may make it difficult to remove the safety pin in
an emergency.
Why
do some jurisdictions insist on using ASTTBC certified technicians?
At
this point in time, A.S.T.T.B.C.
is not recognized in a number of municipalities in the Lower Mainland.
Regardless, mandating proper training and recognizing qualified individuals
is still within the jurisdiction of your local fire marshal. A.S.T.T.B.C.
continues to advocate for official recognition in all the Province's
jurisdictions. Until they're successful, check with your authority
to ensure compliance with the local testing requirements of your fire
fighting and detection apparatus. Employing A.S.T.T.B.C.
Registered Fire Protection
Technicians (RFPT's) ensures you
benefit from the ongoing training and upgrade programs these professionals
are required to undertake.
Should we ever have to replace or upgrade our
extinguishers?
There is no
actual requirement to upgrade the fire extinguishers in your building if they meet the classification
for the type of fire that you can reasonably expect to encounter in the area it protects. You may wish to consider
an upgrade to a "clean agent" extinguisher if the discharge of a normal dry chemical unit in a
specific area might harm or otherwise damage delicate equipment (such as computers or sensitive
electronics). The latest release of NFPA 10 (the National Fire Code on which most jurisdictions
base their rules and policies) states that "dry chemical stored pressure extinguishers manufactured
prior to October 1984 shall be removed from service at the next six year maintenance interval or at the
next hydrotest interval, whichever comes first" (NFPA 10-2007 4.4.1). You should consult with your local
fire department to determine if they intend on enforcing this policy.
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