Fire Safety and Fire Extinguisher

Basic types of fire extinguishers

The two most common types of extinguishers are pressurized dry chemical (Type BC or
ABC, left) and carbon dioxide (CO2, right) extinguishers:

Which kind of extinguisher should I use?

Fire is classified into five general categories
o

Class A fires are ordinary materials like burning paper, lumber, cardboard, plastics etc.

Class B fires involve flammable or combustible liquids such as gasoline, kerosene, and co

Class C fires involve energized electrical equipment, such as appliances, switches, panel b

Class D fires involve combustible metals, such as magnesium, titanium, potassium and so

Class K fires are kitchen fires. This class was added to the NFPA portable extinguishers St

Some fires may be a combination of these! Your fire extinguishers should have ABC
ratings on them. These ratings are look something like "3-A:40-B:C". Higher numbers
mean more firefighting power. In this example, the extinguisher has a good firefighting
capacity for Class A, B and C fires.
Here are some typical extinguishers and their uses:
o Water extinguishers (not pictured and not found in laboratories) are suitable for
class A (paper, wood etc.) fires, but not for class B, C and D fires such as burning
liquids, electrical fires or reactive metal fires. In these cases, the flames will be
spread or the hazard made greater! Water mist extinguishers are suitable for class
A and C; see below.
o Dry chemical extinguishers are useful for either class ABC or class BC fires
(check the label) and are your best all around choice for common fire situations.
They have an advantage over CO2 and "clean agent" extinguishers in that they
leave a blanket of non-flammable material on the extinguished material which
reduces the likelihood of reignition. They also make a terrible mess - but if the

choice is a fire or a mess, take the mess! Note that there are two kinds of dry
chemical extinguishers:

Type BC fire extinguishers contain sodium or potassium bicarbonate.

Type ABC fire extinguishers contain ammonium phosphate.

When to use (or not use) Dry Chemical Extinguishers?

Dry chemical extinguishers can be quite corrosive to metals such as aluminum
and are also potentially abrasive. ABC extinguishers are much more corrosive
than BC extinguishers because the ammonium phosphate agent can undergo
hydrolysis to form phosphoric acid and because the molten agent flows into
minute cracks.
For this reason, dry chemical ABC extinguishers are not recommended for
use on aircraft or electronics such as computers, MRI scanners, and scientific
instruments. Boeing has stated in a service letter "Dry chemical extinguishers
can cause extensive corrosion damage to airplane structure, electrical systems,
and electronic equipment...Dry chemical fire extinguishers should only be used
for airplane firefighting if there are no other extinguishers available and there is
imminent danger to property or personnel."

Proper planning can avoid situations where you might have to make a
choice between extinguisher types. Ensure that the extinguishers closest to
your computers or aircraft are of an approriate type (if local fire codes
permit) and that workers in those areas are trained on when and how to use
them. And remember, if your computer or airplane is fully engulfed in
flames or a person is in danger, then possible added damage from an ABC
extinguisher is moot.

o CO2 (carbon dioxide) extinguishers are for class B and C fires. They don't work
very well on class A fires because the material usually reignites. CO2
extinguishers have an advantage over dry chemical in that they leave behind no
harmful residue. That makes carbon dioxide (or Halotron I or FE-36; see below) a
good choice for an electrical fire involving a computer or other delicate
instrument. Note that CO2 is a bad choice for a flammable metal fires such as
Grignard reagents, alkyllithiums and sodium metal because CO2 reacts with these
materials. CO2 extinguishers are not approved for class D fires!

o Carbon dioxide extinguishers do not have pressure gauges because carbon dioxide
is a condensable gas. Thus, pressure does not tell you how much agent remains in
the cylinder. Instead, the extinguisher should have a tare (empty) weight stamped
on it. To determine the amount of carbon dioxide remaining in the extinguisher,
subtract the tare weight from the current weight.
o Metal/Sand Extinguishers are for flammable metals (class D fires) and work by
simply smothering the fire. The most common extinguishing agent in this class is
sodium chloride, but there are a variety of other options. You should have an
approved class D unit if you are working with flammable metals. The following
types of class D extinguishing units are available through our on-line store, Safety
Emporium.

Sodium chloride (NaCl) works well for metal fires involving magnesium,
sodium (spills and in depth), potassium, sodium/potassium alloys, uranium
and powdered aluminum. Heat from the fire causes the agent to cake and
form a crust that excludes air and dissipates heat.

Powdered copper metal (Cu metal) is preferred for fires involving lithium
and lithium alloys. Developed in conjunction with the U.S. Navy, it is the
only known lithium fire fighting agent which will cling to a vertical
surface thus making it the preferred agent on three dimensional and
flowing fires.

Graphite-based powders are also designed for use on lithium fires. This
agent can also be effective on fires involving high-melting metals such as
zirconium and titanium.

Specially-designed sodium bicarbonate-based dry agents can suppress

fires with most metal alkyls, pyrophoric liquids which ignite on catact
with air, such as triethylaluminum, but do not rely on a standard BC
extinguisher for this purpose.

Sodium carbonate-based dry powders can be used with most Class D fires
involving sodium, potassium or sodium/potassium alloys. This agent is
recommended where stress corrosion of stainless steel mus be kept to an
absolute minimum.

o Water mist extinguishers are ideal for Class A fires where a potential Class C
hazard exists. Unlike an ordinary water extinguisher, the misting nozzle provides
safety from electric shock and reduces scattering of burning materials. This is one
of the best choices for protection of hospital environments, books, documents and
clean room facilities. In non-magnetic versions, water mist extinguishers are the
preferred choice for MRI or NMR facilities (see warning box below) or for
deployment on mine sweepers.

Using fire extinguishers

You are not required to fight a fire. Ever. If you have the slightest doubt about your
control of the situation DO NOT FIGHT THE FIRE.
1. Use a mental checklist to make a Fight-or-Flight Decision. Attempt to use an
extinguisher only if ALL of the following apply:
The building is being evacuated (fire alarm is pulled)

The fire department is being called 999.

The fire is small, contained and not spreading beyond its starting point.

The exit is clear, there is no imminent peril and you can fight the fire with your back to

You can stay low and avoid smoke.

The proper extinguisher is immediately at hand.

You have read the instructions and know how to use the extinguisher.

IF ANY OF THESE CONDITIONS HAVE NOT BEEN MET, DON'T FIGHT

THE FIRE YOURSELF. CALL FOR HELP, PULL THE FIRE ALARM AND
LEAVE THE AREA.

If you have any doubt about your personal safety, or if you can not extinguish a fire,
leave immediately and close off the area (close the doors, but DO NOT lock them).
Leave the building but contact a firefighter to relay whatever information you have
about the fire.
2. Pull the pin on the fire extinguisher.
3. Stand several feet from the fire, depress the handle and sweep back and forth
towards the fire. Note:

Do not walk on an area that you have "extinguished" in case the fire
reignites or the extinguisher runs out! Remember: you usually can't expect
more than 10 full seconds of extinguishing power on a typical unit and this
could be significantly less if the extinguisher was not properly maintained
or partially discharged.

The metal parts of CO2 extinguishers tend to get dangerously cold -practice using one beforehand or have someone show you the proper way
to hold one.

Again, proper training is usually required by state or federal OSHA!

4. Direct the extinguisher at the base of the flames until the fire is completely out.
5. Recharge any discharged extinguisher immediately after use. If you discharge an
extinguisher (even just a tiny bit) or pull the pin for any reason, call your campus
or corporate Fire Marshal's office to arrange a replacement.

Care and Maintenance of Your Extinguisher

At least once a month (more often in severe environments) you should inspect your
extinguisher. Ensure that:
a.

The extinguisher is not blocked by equipment, coats or other objects that

could interfere with access in an emergency.

b.

The pressure is at the recommended level. On extinguishers equipped with

a gauge (such as that shown on the right) that means the needle should be in the
green zone - not too high and not too low.

c.

The nozzle or other parts are not obstructed.

d.

The pin and tamper seal (if it has one) are intact.

e.

There are no dents, leaks, rust, chemical deposits and other signs of
abuse/wear. Wipe off any corrosive chemicals, oil, gunk etc. that may have landed
on the extinguisher.

f.

Some manufacturers recommend shaking your dry chemical extinguishers

once a month to prevent the powder from settling/packing. We are dubious this has
any value ,but you are going to pick it up to inspect it anyway, so why not give it a
good shake?

g.

Fire extinguishers should be pressure tested (a process called hydrostatic

testing) after a number of years to ensure that the cylinder is safe to use. Consult
your owner's manual, extinguisher label or the manufacturer to see when yours
may need such testing.

If the extinguisher is damaged or needs recharging, get it replaced immediately!

One more time: Recharge all extinguishers immediately after use regardless of how
much they were used.