Different fires require different extinguishing methods, and using the wrong one can make a fire worse or put you in danger. Fires are grouped into five classes based on what’s burning: ordinary materials like wood and paper (Class A), flammable liquids (Class B), electrical equipment (Class C), combustible metals (Class D), and cooking oils and fats (Class K). Each class has specific agents that work and specific agents that are dangerous to use. Here’s what you need to know about each one.
Class A: Wood, Paper, and Cloth
Class A fires involve ordinary combustible materials: wood, paper, cardboard, fabric, rubber, and most plastics. These are the most common fires in homes and offices, and they’re the most straightforward to fight. Water is your primary tool. It works by cooling the fuel below its ignition point and physically separating the burning material from oxygen.
Foam extinguishers are also effective on Class A fires and add an extra layer of protection. The foam creates a blanket of bubbles over the burning surface that blocks oxygen, insulates the fuel to prevent re-ignition, and reflects radiant heat away from nearby materials that haven’t caught fire yet. The increased surface area of foam bubbles absorbs heat far more effectively than plain water droplets alone. For a small Class A fire, like a wastebasket or campfire, water from any source will work. For larger fires, a pressurized water or foam extinguisher gives you the reach and volume you need.
Class B: Flammable Liquids
Class B fires burn in flammable liquids: gasoline, alcohol, oil-based paints, ether, solvents, and grease that isn’t in a cooking appliance. The critical rule here is never use water. Water is denser than most flammable liquids, so it sinks beneath the burning fuel and can cause it to splash and spread violently. A small gasoline fire can become a large one in seconds if you hit it with a stream of water.
The correct approach is smothering. You need to cut off the fire’s oxygen supply without disturbing the liquid surface. Carbon dioxide (CO2) extinguishers displace oxygen around the fire and leave no residue. Dry chemical extinguishers coat the fuel with a powder that interrupts the chemical reaction sustaining the flames. Foam extinguishers designed for Class B fires float a blanket on top of the liquid, sealing off oxygen and suppressing flammable vapors. If you’re near a small container of burning liquid and have no extinguisher, sliding a metal lid over the container to starve it of air can work, but never try to carry a burning container.
Class C: Electrical Fires
Class C fires involve energized electrical equipment: appliances, wiring, circuit breakers, outlets, and power tools. The danger isn’t just the fire itself but the live electrical current running through it. Water and foam are both conductive, so using either on a Class C fire can send electricity back through the stream and electrocute you.
CO2 and dry chemical extinguishers are the standard choices because they’re non-conductive. If you can safely disconnect the power source, do that first. Once the equipment is de-energized, the fire reclassifies based on whatever is actually burning (usually Class A materials like insulation, plastic housings, or paper). At that point, water becomes safe to use. The key judgment call is knowing whether the power is truly off. If you’re unsure, treat it as a Class C fire and stick with non-conductive agents.
Class D: Combustible Metals
Class D fires are rare outside of industrial and laboratory settings, but they’re uniquely dangerous. Combustible metals like magnesium, titanium, sodium, lithium, potassium, and zirconium burn at extremely high temperatures. Water, CO2, and standard dry chemical extinguishers can all react violently with burning metals, sometimes causing explosions or intensifying the flames.
These fires require specialized dry powder agents. Graphite powder and granular sodium chloride (essentially table salt in a specific form) are the two most common substances used. They work by smothering the burning metal and absorbing heat without reacting with it. Class D extinguishers are designed to apply these powders gently so they don’t scatter the burning metal. If you work around combustible metals, the extinguisher should be specific to the metal you’re handling, since not every dry powder agent works on every metal.
Class K: Kitchen Grease and Cooking Oil
Class K fires happen in cooking oils and fats, whether animal-based or vegetable-based. They’re the leading cause of home kitchen fires, and they’re one of the most dangerous to handle incorrectly. Throwing water on a grease fire is one of the most common and catastrophic mistakes people make. Water hitting superheated oil (which can exceed 600°F) instantly turns to steam, explosively launching burning oil into the air and across the kitchen.
Wet chemical extinguishers are designed specifically for Class K fires. They spray a fine mist of a potassium-based solution that reacts with the hot cooking oil through a process called saponification, essentially turning the surface of the oil into a soapy foam layer. This layer sits on top of the fuel, smothers the flames, and cools the oil below its ignition point all at once.
Using a Fire Blanket on a Stovetop Fire
For a pan fire on your stove, a fire blanket is often the fastest and safest option. Here’s the correct sequence:
- Turn off the heat source first. If you can’t safely reach the controls, skip this step and come back to it.
- Pull the blanket from its container by the fabric straps. Wrap the top edge around your hands to protect them from the flames.
- Place the blanket over the pan. Don’t throw it. Stretch it out fully and lay it gently over the burning pan so it covers the entire opening.
- Leave it in place for at least 30 minutes. Grease fires can reignite quickly if oxygen reaches the oil while it’s still above its ignition temperature.
If the fire is larger than the blanket can cover, or if it has already spread beyond the pan, leave the room, close the door behind you, and call the fire department.
How to Use a Fire Extinguisher
Regardless of the type, all portable fire extinguishers follow the same four-step operation known as the PASS method:
- Pull the safety pin at the top of the extinguisher.
- Aim the hose or nozzle at the base of the fire, not at the top of the flames.
- Squeeze the handle to release the extinguishing agent.
- Sweep the nozzle from side to side across the base of the fire.
Aiming at the base is the single most important detail. Spraying into the flames themselves wastes your agent on fire that’s already consuming itself. The base is where the fuel meets the fire, and that’s where you break the cycle. Most portable extinguishers empty in 10 to 20 seconds, so precision matters more than volume.
Matching the Right Extinguisher to the Fire
Every fire extinguisher has a label showing which fire classes it’s rated for. Many home extinguishers are rated ABC, meaning they use a dry chemical agent that works on ordinary combustibles, flammable liquids, and electrical fires. This is a solid all-purpose choice for most residential situations. Kitchen extinguishers rated for Class K fires are a separate, important addition if you cook with oil regularly.
The most dangerous scenario isn’t having no extinguisher. It’s using the wrong one. Water on a grease fire spreads it. Water on an electrical fire can electrocute you. A standard dry chemical on a lithium fire can cause an explosion. Before you ever need to use an extinguisher, check the label and know what it covers.
Inspect your extinguishers periodically. OSHA requires all firefighting equipment to be maintained in operating condition, with portable extinguishers inspected and serviced on a regular schedule. At home, a quick monthly check is simple: make sure the pressure gauge needle is in the green zone, the pin and tamper seal are intact, and there’s no visible damage or corrosion. Replace or recharge any extinguisher that’s been partially used, even briefly, since you can’t count on the remaining charge in an emergency.