An Intro to Fire Science: The Classifications of Fires

Fighting fires is an important science because it can save lives. Classifying fires allows firefighters to choose the appropriate fire-fighting agent to extinguish a fire. Each class of fire designates the fuel involved in the fire, such as wood, gas, or metals. Firefighters then can choose the most appropriate extinguishing agent to put out that fire, as well as avoid severe injuries. Fire Extinguisher 101 has the most comprehensive information about fire classes online. Throughout this article you will find links to their website, as well as quoted information about various methods on how to fight those different fires.

Fire Groups

Extinguishing Tire Fire

Class A — Ordinary combustibles: Class A fires involve common combustibles such as wood, paper, cloth, rubber, trash and plastics. They are the most common type of fires in typical commercial and residential settings, but can occur anywhere these types of materials are found. Both water and fire extinguisher foam are effective to control this type of fire.

Class B — Flammable liquid and gas: Class B fires involve flammable liquids’ gases, solvents, oil, gasoline, paint, lacquers, tars, and other synthetic or oil-based products such as. Fire Extinguisher 101 lists the most common of these liquids as:

  • Gasoline and diesel
  • Ethanol and methanol
  • Isopropanol
  • Acetone
  • Acetylene
  • Methane
  • Butane
  • Propane

It is easy to be caught off guard by this type of fire, since many of these materials are generally dormant. Foam, as opposed to water, is the best defense for this type of fire, as it will reduce the amount of oxygen getting to the flame by smothering it. Some instances are more specific, according to Fire Extinguishers 101. “In the case of a kitchen stovetop fire, sodium bicarbonate (baking soda) or potassium carbonate are effective ways to smother the flames. It is smart to keep these ingredients close at hand.” And more generally speaking, “CO2, which is commonly available in extinguishers, is another effective weapon against this designation of fire.”

Class C — Electrical: Class C fires involve energized electrical equipment, such as wiring, controls, motors, data processing panels or appliances. They can be caused by a spark or power surge and typically occur in locations that are difficult to reach and see. Other sources of electrical fires include overloaded electrical outlets; incorrectly wired plugs, outlets, and switches; and short-circuits.

Class D — Metal: Class D fires involve combustible metals such as magnesium and sodium. Combustible metal fires are unique industrial hazards which require special dry powder agents. On the plus side, larger pieces of these metals typically do not pose a threat, as their size disperses the heat throughout. However, if one of these metals should ignite, water can never be used, as it will energize the flame, with the potential to increase the damage. The best way to prevent this is to keep the aforementioned extinguishers with dry powder agents on hand around these combustible metals. However, know the difference between dry powder agents, and dry chemical agents; the latter can increase the spread of a Class D fire.

Kitchen Fire

Class K — Cooking oils and fats: Class K stands for “Kitchen Cooking,” and those fires involve combustible cooking materials such as oils and grease commonly found in commercial and residential kitchens. Kitchens that use these combustible ingredients require the possession of a special wet chemical extinguishing agent that is specially suited for extinguishing and suppressing these extremely hot fires that have the ability to reflash. The following oils and fats provide examples of the origins of this type of fire:

  • Vegetable oils like canola, corn, and safflower
  • Olive oil
  • Butter
  • Margarine
  • Lard
  • Bacon grease

Ask anyone in a kitchen could tell you, it is not fun to get splashed by cooking oil. It happens pretty often, but generally in small doses. But if an extreme amount of oil were to ignite, the results could be life-threatening. Fire extinguishers rated for use with class K fires always contain a wet chemical extinguishing agent that turns burning cooking oil and fat into soap. Local building codes will dictate the design and equipment used for businesses such as restaurants and cafeterias. Likewise, these businesses should make sure all of their employees are properly trained as to how to handle fires of all classes.

Fire Extinguishers and Other Safety Measures

Controlled Burn

Residents and businesses are encouraged and sometimes required to have fire extinguishers on site to help extinguish fires before they get out of control. Fire extinguishers are organized according to fire classifications, so residents and business owners can know which fire extinguishers to have on hand. Labels on extinguishers indicate the class and relative size of fire that they can be expected to handle.

Portable fire extinguishers are classified to indicate their ability to handle specific classes and sizes of fires. The type of extinguisher generally correlates to the type of fire it is meant to put out. Class A extinguishers are used on fires involving ordinary combustibles, such as wood, cloth, and paper. Class B extinguishers are used on fires involving liquids, greases, and gases. Class C extinguishers are used on fires involving energized electrical equipment. Class D extinguishers are used on fires involving metals such as magnesium, titanium, zirconium, sodium, and potassium.

The recommended marking systems used to indicate the extinguisher suitability according to class of fire is a pictorial concept that combines the uses and non-uses of extinguishers on a single label. Learn more about those symbols as well as how to use a fire extinguisher before you commit to using those fire-fighting tools. Other safety measures include smoke alarms and escape plans, which often can save more lives than a fire extinguisher used improperly.

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