While fire can seem like one big threatening force, it’s important to know that there are actually several classes of fires. A fire’s class can determine how quickly it burns, how dangerous it is, and the best way to suppress or put it out. The 5 different classes of fires each have their own best approach to put them out safely and effectively. 

The 5 Different Classes of Fires

The 5 main classes of fires are categorized by what caused the fire or what the fire uses as fuel, and are as follows:

  • Class A: solid materials such as wood or paper, fabric, and some plastics
  • Class B: liquids or gas such as alcohol, ether, gasoline, or grease 
  • Class C: electrical failure from appliances, electronic equipment, and wiring
  • Class D: metallic substances such as sodium, titanium, zirconium, or magnesium 
  • Class K: grease or oil fires specifically from cooking 

Understanding the 5 different classes of fires can help you determine the biggest fire risks at your facility, depending on the fuels and fire hazards present as well as how best to prepare in case of a fire emergency.

Let’s break down each of the 5 different classes of fires more thoroughly.

Class A Fires: “Ordinary” Fires

Class A fires are the most common of the 5 different classes of fires. They occur when common combustible materials like wood, paper, fabric, trash, and light plastics catch fire. These accidental fires are ubiquitous across a variety of industries, so it’s recommended to have adequate protection against “ordinary” fires in addition to other condition-specific fires.

Despite being “ordinary”, don’t rule this class of fire as low-risk. If there’s an abundance of fuel present, these fires can intensify quickly. It’s best to put out a Class A fire quickly before it spreads using water or monoammonium phosphate.

Class B Fires: Liquids & Gases

Class B fires involve flammable liquids and gases, especially fuels like petroleum or petroleum-based products such as gasoline, paint, and kerosene. Other gases that are highly flammable are propane and butane, which are common causes of Class B fires. The best way to deal with these types of fires is by smothering them or removing oxygen using foam or CO2 fire suppression equipment.

Be aware that Class B fires do not include grease fires or cooking fires, which belong to their own class, Class K.

Class C Fires: Electrical Fires

Electrical fires fall under Class C and are common in facilities that make heavy use of electrical equipment, but they can occur in a wide range of industries. For example, data centers might be an obvious risk area for Class C fires. They must have safeguards in place to deal with electrical fires. 

Construction sites are another common Class C fire risk: electrical power tools or appliances used for cooking can cause sparks to ignite combustible materials and intensify rapidly. Old buildings with bad wiring or space heaters present more concerns.

Electrical fires require non-conductive materials to extinguish the flame, so water alone is not a good solution. Facilities with sensitive equipment may prefer clean agent suppression because it won’t leave residue or damage electrical equipment.

Class D Fires: Metallic Fires

Class D fires are not as common as the other classes, but they do require special attention because they can be especially difficult to extinguish. Metallic fires involve flammable materials like titanium, aluminum, magnesium, and potassium — all commonly occurring in laboratories. 

Class D fires cannot be addressed with water, as this can exacerbate the fire and be potentially dangerous. Dry powder agents are the best solution for smothering the flames and limiting damage to property or people.

Class K Fires: Grease Fires or Cooking Fires

Class K fires involve flammable liquids, similar to Class B fires, but are specifically related to food service and the restaurant industry. These common fires start from the combustion of liquid cooking materials including grease, oils, and vegetable and animal fats. 

Because they can spread quickly and be difficult to manage, Class K fires are some of the most dangerous. Water can make the situation worse, but smothering the flames or using a wet agent fire extinguisher is effective. 

Now that we understand how each fire starts, we can prepare for how to fight them — or better yet, prevent them from happening in the first place.

How to Prepare for the 5 Different Classes of Fires

Being ready for whatever fire danger involves three areas of focus: equipping yourself with the right fire extinguisher for your corresponding fire classes, committing to regular fire safety training, and keeping all equipment in peak condition. If you can maintain each of these, you should be able to react appropriately in a fire emergency — no matter what class of fire you face.

Choose the Right Fire Extinguisher

Different types of fire extinguishers exist in order to address the 5 different classes of fires. Each fire class describes the fuel or material a fire is burning or what caused it to start — therefore, using the right extinguisher is essential to put out the fire safely. 

Here’s a quick chart to help you identify the right fire extinguisher for each class of fire.

Fire Class Fuel Type How to Suppress Fire Extinguisher Type
Class A Freely burning combustibles Water, Smothering ABC/powder, water, water mist, foam
Class B Burning liquid or gas Smothering ABC/powder, CO2, water mist, clean agent 
Class C Electrical fire Non-conductive chemicals ABC/powder, CO2, water mist, clean agent
Class D Metallic fire Dry powder agent Powder
Class K Cooking or grease fire Smothering, wet chemical  Wet chemical, water mist

Complete Regular Training

Make sure staff know how to operate a fire extinguisher and when it’s needed, especially for the classes of fire you are most likely to face. Help staff understand how to tell when a fire is too advanced to address themselves, and when and how to contact the authorities promptly. Commit to regular fire safety training to stay current on preparedness skills, technology, and equipment.

Pair your fire extinguisher training with a practiced evacuation plan. Make sure your plan is clearly posted and all people inside your building can easily access the evacuation route in case of emergency.

Keep Up with Testing and Maintenance

Remember to have equipment inspected regularly, and replace fire extinguishers once they pass their expiration. You’ll also need to have your building inspected by the local fire department to ensure that it meets fire codes regarding your fire protection system, building capacity, and fire alarm requirements.

No matter what class of fire you’re protecting against, Vanguard Fire & Security Systems has the tools, technology, and expertise you need. From fire safety training to fire suppression system installation, testing, and maintenance, we can help.