Most local municipalities estimate the number of fire extinguishers needed by the
total square feet of the area to be protected divided by 3,000. As an example, a
retail location with 4,000 sqft. would require a minimum of two fire extinguishers.
Portable extinguishers should be located where they are visibly accessible in case
of a fire. NFPA 10, 6.1.3.
Extinguishers weighing 40 lbs. or less should be installed so that the top of the
extinguisher is no more than 5 feet above the floor. For those weighing more than
40 lbs., the top of the extinguisher should not be more than 3.5 feet above the
floor. In both cases the distance between the bottom of the extinguisher and the
floor can never be less than 4 inches.
Placement is dependent on the area being covered, the size of the extinguisher,
and the hazard classification for the area being covered. Some local requirements
may be more strict, so you should always check with your local fire marshal.
Fire Class Travel Distance*
Class A - 75 feet
Class B - 50 feet
Class C - Based on appropriate A or B hazard
Class D - 75 feet
*Travel distance is the actual distance an individual needs to walk to reach the
fire extinguisher and must take into account the effect of doorways, partitions
or other obstacles.
A thorough examination of the basic elements of the fire extinguisher performed
by a licensed professional who has undergone the necessary training must be conducted
A thorough examination and service of the fire suppression system performed by a
licensed professional who has undergone the necessary training and has all service
manuals must be conducted semi-annually (every six months).
Determine the accessibility and visibility of the fire extinguisher.
If appropriate, check the gauge to see that it is in the green area.
Check for visible signs of damage.
If an inspection reveals that discharge, damage or tampering has occurred, the unit
must be taken out of service. A spare fire extinguisher of equal or greater rating
needs to be installed while service is performed.
Fire extinguishers are distinguished based on the types of fires on which they are
effective. These fires are classified by their fuel source and assigned identifying
letters as follows:
CLASS A – Fires that result from ordinary combustibles, such as wood and paper.
CLASS B – Fires that result from combustible liquids, such as kerosene, gasoline,
oil, and grease.
CLASS C – Fires of an electrical nature. These result from the combustion of circuit
breakers, wires, outlets, and other electrical devices and equipment. Extinguishers
designed to handle this type of fire cannot use chemicals that are conductive since
conductive agents increase the risk of electric shock to the operator.
CLASS D – Fires resulting from combustible metals, such as sodium, potassium, titanium,
and magnesium. These fires occur mostly in chemical laboratories and are rare in
most other environments.
CLASS K – These types of fires consume vegetable oils, animal fats, and generally
happen in commercial kitchens.
To prevent confusion, extinguishers are classified by the type of chemical agents
they contain as no fire extinguisher can be safely and effectively used for every
type of fire. A few of the most common extinguisher types are listed below:
Dry Chemical – There are two types of fire extinguishers that use a dry chemical.
Multi-purpose dry chemical - ammonium phosphate
Effective on “A,” “B,” and “C” class fires. This chemical is corrosive and must
be scrubbed from surfaces after use. These types of extinguishers are very common
and are found in schools, homes, hospitals and offices.
Regular dry chemical - sodium bicarbonate
Effective on “B” and “C” class fires. These extinguishers are found in garages,
kitchens and laboratories. Sodium bicarbonate is easy to clean and non-toxic.
These extinguishers contain liquid CO2 that is expelled as a gas. They are effective
against “B” and “C” class fires. Unlike other chemicals, CO2 does not leave a harmful
residue and is environmentally friendly. It also poses very little danger to electronics
and is effectively employed in laboratories, computer rooms, and other areas with
These extinguishers are most suited for “A” class fires. However, they cannot be
used in “B,” “C” or "D" class fires. In "B" and "D" class fires, the water will
spread the flames. In a "C" class fire, the water is conductive and poses a risk
of electric shock to the operator. However, the misting nozzle of a "Water Mist"
extinguisher breaks up the stream of deionized water so that there is no conductive
path back to the operator. Since the agent used is water, these types of extinguishers
are inexpensive and environmentally friendly.
Wet Chemical Fire Extinguishers
These devices are designed to combat “K” class fires and commonly use potassium
acetate. They are appropriately employed in commercial kitchens and restaurants,
especially around deep fryers. The chemical is emitted as a fine mist that does
not cause grease to splash onto other surfaces. They can also be used in “A” class
Newer devices have pictures that correspond directly to the fire types listed above.
Older models have letters that serve the same purpose.
A numerical rating that designates the extinguishing potential for that particular
Instructions for operation.
A tag that indicates if and when an inspection occurred.
Fire extinguishers can expire for a few different reasons.
One common way is that, over time, the seal on the neck will weaken and allow compressed
gas to escape. Extinguishers that have lost much of their pressure will not operate.
Pressure within an extinguisher can be conveniently checked through a pressure gauge.
“ABC” class extinguishers (ammonium phosphate) have the tendency to fail due to
solidification of the chemical in the canister base.
Commercial extinguishers that have expired, can be refilled and resealed by companies
who specialize in this service. Inexpensive home models are generally disposable
and can not be serviced.
Unfortunately, an expiration date cannot be fully trusted and there is no foolproof
way to know if an extinguisher is no longer functional. Due to the extremely destructive
potential of fires and the relatively low cost of extinguishers, it is advisable
to replace or recharge questionable extinguishers.
An internal examination of an emptied fire extinguisher. The examination will check
for corrosion and interior problems. Extinguishers passing the six year maintenance
are then reassembled, recharged, and receive a six year service label and a verification
of service collar.
Pressure testing of a fire extinguisher to confirm its strength against unwanted
rupture that is performed by a trained professional to requalify cylinders.
Testing is required at the following intervals:
Dry Chemical - 12 years
Class K, water, AFF, FFFP - 5 years
Halogenated Agent - 12 years
Carbon Dioxide - 5 years