A fire can strike anywhere at any moment, leaving a deadly path of destruction. While smoke alarms are your first line of defense of warning about impending danger, fire extinguishers can help prevent an emergency situation turn into pure devastation.

The concept of a fire extinguisher has been around for a couple of thousands of years when Ctesibuius of Alexandria invented a pump that pumped water used to extinguish fires. However, in 1818, George William Manby, a British Captain, invented the modern fire extinguisher. It was made from copper, capable of holding three gallons of the extinguishing agent potassium carbonate (a dry chemical) and compressed air.

In the US, there are five Classes of fires based on the properties of the fire- A, B, C, D, and K. It is important to understand the different Classes and use the correct extinguishing method because of the consequences from using the wrong method range from no effect to an explosion.


Class A  – Common Combustible Materials

Class A fires are the most common fire encountered in a home or workplace. The culprits that usually cause a Class A fire are – paper, wood, fabric, plastics, and garbage.

These fires are contained by water or mono ammonium phosphate, the chemical compound commonly used in fire extinguishers.

Class B  – Flammable Liquids and Gases

Although Class B fires can be found in residential settings, oil, grease, paint, and solvents and flammable gases, such as – methane and propane that cause Class B fires are more prevalent in commercial and industrial environments.

In the case of Class B fires, water will do more damage than good because instead of extinguishing the fire, it can disperse the flammable liquids causing the fire to spread. For this reason, an extinguishing method that smothers it by removing the oxygen from the fire or extinguishes the fire through a chemical reaction must be used. Two choices are –

  • Monoammonium phosphate – Also used in Class B because it displaces the needed oxygen from the fire.
  • Sodium bicarbonate – is an example of the second choice because it uses a chemical reaction to distinguish the fire.

Class C  – Live Electrical Sources

Class C fires, known as electrical fires, can occur in residential or commercial settings on any scale. Therefore, every home and industry needs a plan of action in case of an electrical fire.

The plan should contain two important steps –

  1. Disconnect the electrical origin or supply
  2. Use a non-conductive chemical to extinguish the flames – mono ammonium phosphate and sodium bicarbonate may be used for Class C fires

Class D  – Combustible Metals

The least common fire class however it can rapidly become intense, spread and cause excessive damage.  Class D fires originate from combustible metals including – titanium, potassium, magnesium, and aluminum.

Even though Class D fires are most common in laboratories, they can also be found in industrial settings as well.  Since Class D fires are caused by combustible metals, they present a unique challenge to extinguish. Just as with Class C, water is never to be used on fire that burn metal. In fact, spraying water on it will only energize the flames causing additional heat and more damage.

To effectively handle Class D fires, dry powder extinguishing agents that absorb heat and cut the oxygen off to the flames, essentially smothering them, will need to be used. Wherever there is a risk of a metal fire, an extinguisher containing dry chemical agents should be on hand. Look for extinguishers that include graphite in powder form and sodium chloride in granular form. Also, special training should be provided on how to properly use these agents.

Class K  – Commercial Cooking Equipment

Class K fires, otherwise known as kitchen fires, they can be found in residential settings, but often a special concern for the commercial food industry. Technically, Class K fires are a subset of Class B because it involves flammable liquids. However, Class K fires have unique characteristics and handled differently because they burn a certain type of liquid – fats, and oils and often much hotter.

Only use fire extinguishers rated for Class K with kitchen grease fires. They contain a specially designed wet chemical agent that turns the liquid fueling the fire to soap.


Understanding the different classes of fire and how to extinguish them can help you and your family prevent a devastating situation. To be sure your home and business is code-compliant with all local and state ordinances, contact a contractor, fire or sprinkler engineer.

AUTHOR’S BIOMichael Tobias is the founder and principal of Chicago Engineers. He is a graduate of Georgia Tech class of 2004, with a Bachelor of Mechanical Engineering with honors. His innovative approach to MEP engineering comes from graduating GE’s Engineering Leadership Program, where he designed wind turbines and biofuel power plant engines. Michael’s passion within design is energy efficiency and green technology.