Classifications of Fire &
Fire Extinguishing Agents
Fires are classified by letters A through D. Within each
class fires involve materials with similar burn properties and require similar
extinguishing agents. Most fuels are found in combinations, however, and for
firefighting purposes there are actually seven possible fire classes described
below.
In order to successfully put out a fire you need to use
a suitable extinguishing agent [chart] that will extinguish in the least amount of
time, cause the least amount of property damage and minimize threat to life.
Three things are needed to make a fire: heat, fuel and air. Remove any one of
them and the fire is extinguished.
1. Class A Fires
Fires of combustible solids such as wood, paper and plastic are best put
out by water. Foam and chemicals may also be used, but Thermo-Gel is our
preferred choice for Class-A fires because it improves the effectiveness of
water better than foam and acts as a cooling agent for an extended time
period.
2. Class B
Fires Fires caused by flammable liquids such
as oil, gas and grease give off flammable vapor and require smothering agents.
Dry chemical, foam and carbon dioxide (CO2) may be used but Thermo-Gel cannot
be used. If fire is supplied with fuel by an open valve or broken line the
source must be shut down ASAP. This action alone may stop the fire so it is
part of our design process for industrial projects. If a fuel source is not
turned off immediately an explosive hazard exists which can be more dangerous
than the fire itself. Water on a Class B fire may actually spread the fire
rather than putting it out.
3. Combination
Class A and B Fires Water fog and foam may be
used to smother fires involving both solid fuels and flammable liquids or
gases. These agents also have a cooling effect on the fire. In enclosed spaces
CO2 may also be use but since it robs oxygen from the fire it may also
suffocate people not using supplemental oxygen and extreme caution must be
used.
4. Class C
Fires Electrical fires. Certain non-conducting
extinguishing agents must be used such as CO2 and dry chemical. Water and
wetting agents like Thermo-Gel cannot be used. Note that dry chemical may ruin
electronic equipment. The equipment must be de-energized or electric shock may
occur in addition to any damage from the actual fire.
5. Combination
Class A and C Fires Since electrical equipment
is involved in this type of fire only non-conducting agents such as CO2 or dry
chemicals may be used. Water and wetting agents like Thermo-Gel cannot be
used. The equipment must be de-energized or electric shock may occur in
addition to any damage from the actual fire.
6. Combination Class B and C
Fires A non-conducting extinguishing agent such as CO2 or dry
chemical is required. Water and wetting agents cannot be used on this file,
and it is vitally important to shut off both the source of electricity and
fuel ASAP before actual firefighting begins.
7. Class D Fires
Combustible metals such as potassium, sodium, and their alloys,
and magnesium, zinc, zirconium, titanium and aluminum. They burn on the metal
surface at very high temperature, often with a brilliant flame. Water,
Thermo-Gel and dry chemicals should not be used on these fires or splattering
molten metal may actually make the fire worse. Class D fires are smothered and
controlled by dry powders.
|
Fire Extinguishing Agents |
| Agent |
Advantages |
Disadvantages |
| Water |
 | Readily Available |
| Excellent cooling properties |
| Provides protection for fire party |
| Good choice for Class A |
|
| Not to be used
on Electrical Fires |
| Can reduce stability |
| Can spread Class B fires |
| Damages/destroys property |
|
| Thermo-Gel® |
| Improves performance of water |
| Excellent cooling properties |
| Eco- friendly & does not harm structures. |
| Best choice for Class A |
|
| Not to be used
on Class B or C fires |
| Can spread Class B fires |
| Damages electrical equipment |
|
| Foam |
| Smothering agent for burning liquids |
| Minimal chance of re-kindling |
| Readily Available |
| Excellent choice for Class B |
|
| Not to be used
on Electrical Fires |
| Damages/destroys property |
| Better choices available for Class A |
|
| Dry-Chemical |
| Smothering agent |
| Fast, effective and readily available |
| Rated for Class B and C fires |
|
| Minimal Protection against re-flash |
| Highly corrosive to electronic equip.
|
| Agent can cake and solidify in container |
| Ecological concerns |
|
| Carbon Dioxide |
| Safe for Class C |
| Extinguishes almost anything enclosed |
| Non-corrosive, non damaging to equip.
|
| Minimal chance of re-flash in sealed space
|
|
| Sucks oxygen from air - can kill firefighters
|
| No re-flash protection in open spaces
|
|
| Dry Powders |
| Specifically used on Class D fires |
|
| Specialty chemical for Class D only |
| Not as effective on other fire classes |
|
