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What’s burning tells you everything you need to know about how to respond, and it's the reason why knowing fire classes A, B, C, D, & K is so important. 

These are the systems behind how we plan, equip, and act in emergencies. From the paper in an office trash bin to the oil simmering in a commercial kitchen, each class signals a different kind of threat and a different kind of fire extinguisher solution.

At Swartz Fire & Safety, we’ve spent decades helping businesses across Central Pennsylvania match their risk environment with the right protection strategy. Before the sirens, before the smoke, it all starts with knowing what kind of fire you’re facing.

Key Takeaways

• Fire classes A, B, C, D, and K categorize fires by what’s burning, guiding how we prepare and respond.
• Using the correct extinguisher type depends entirely on the fire class involved.
• Swartz Fire & Safety helps match real-world risks with the right fire protection systems across Central PA.

Class A — Everyday Materials, Everyday Risk

Class A fires are the ones most people recognize without realizing it because these involve ordinary combustible materials like paper, wood, cloth, rubber, and some plastics. 

Think breakroom trash bins, stockroom shelving, or stacks of cardboard in a loading dock. These are the fires that start quietly and grow quickly, feeding off the everyday surroundings of most buildings.

You’ll typically find Class A hazards in offices, schools, retail stores, warehouses, and home fires, too. They're so common that they can feel deceptively “basic,” but that familiarity often leads to underestimating the danger, especially when a small fire spreads faster than expected.

The right type of extinguisher for a Class A fire depends on the setting, but standard options include water-based fire extinguishers, foam units, and ABC dry chemical models, which also cover Classes B and C. These portable fire extinguishers are designed to cool and smother the flames, cutting off the oxygen and halting the fire's spread before it consumes nearby property.

Despite being one of the most manageable fire classes, A-class incidents are still responsible for a high number of losses simply because they often start unnoticed and escalate in the early stages.

Class B — Flammable Liquids That Don’t Play Fair

Class B fires are driven by flammable liquids and combustible liquids—fuels like gasoline, oil-based paints, solvents, and propane. What makes them especially tricky is that it’s not the liquid itself that burns but the vapor it gives off. Once ignited, that vapor acts like a fast-moving fuse, making these fires explosive and unpredictable.

You’ll find Class B risks in garages, manufacturing plants, fuel storage areas, and a wide range of industrial spaces where oils or solvents are used. Even in small volumes, these fires can escalate rapidly if the fuel source isn't shut down or suppressed early.

Because water can spread these fires instead of putting them out, you need fire extinguishers designed to interrupt the vapor phase.

Common types of fire extinguishers for Class B include carbon dioxide extinguishers, dry chemical units (both ABC and BC), and foam extinguishers that form a blanket over the liquid surface. In settings with sensitive electronic equipment, clean agent fire extinguishers are sometimes used as a non-conductive option.

Smothering, not soaking, is what ends a Class B fire. That’s why knowing which extinguishing agent to grab can make the difference between a quick stop and a multi-alarm emergency.

Class C — Not “Electrical Fire” But “Energized Fire”

Class C fires aren’t defined by what’s burning. Rather, they’re defined by the presence of electricity. More specifically, they involve energized electrical equipment, which means the current is still flowing through wiring, control panels, circuits, or outlets.

Once that equipment is de-energized, the fire reverts to a Class A or B classification, depending on the material that’s burning.

Because electricity changes the rules, Class C fires require non-conductive extinguishing agents. That’s why carbon dioxide and dry chemical extinguishers are the top picks. They can smother flames and interrupt combustion without posing a risk of electrical shock, which is critical in environments with server rooms, office buildings, labs, or facilities with high-value electrical equipment.

Using the wrong method—like water—on a Class C fire risks damage to equipment and puts people at risk, too. That’s why it’s crucial to recognize Class C not just as an “electrical fire” but as a fire where electricity changes how you fight it.

Class D — Metals That Burn Hotter Than Most People Realize

Class D fires involve combustible metals like magnesium, titanium, sodium, and lithium, which are all materials that aren’t flammable in everyday life but can ignite under the right conditions. You’ll typically find these risks in manufacturing, aerospace, machining, and laboratories where metal dust or shavings are part of the environment.

These fires burn at extremely high temperatures and react violently with water, foam, or even some standard chemical agents. However, dry powder extinguishers specifically formulated for class D fires smother the reaction and create a barrier between the burning metal and surrounding air, cutting off the oxygen needed to sustain the fire.

Not every facility will encounter a Class D risk, but where they do exist, the stakes are high. These are fires involving materials that react unpredictably and require both training and specialized equipment to control. While rare, they’re some of the most dangerous to handle unprepared.

Class K — The Commercial Kitchen’s Hidden Danger

Class K fires are the high-heat hazards of the food service world. They involve cooking appliances and fires fueled by hot oils, grease, vegetable oils, and animal fats—the kinds of fires that don’t behave like typical Class B liquid fires. These substances can reach flash points that make them flare up violently and re-ignite easily if not properly extinguished.

Unlike flammable fuels that can be smothered with foam or CO₂, Class K fires require wet chemical extinguishers. 

These use a fine spray of suppressant to cool the oil and form a soapy film (a process called saponification), which prevents reignition. In commercial kitchens and cooking environments, they’re often paired with built-in kitchen hood suppression systems for fast, automatic response.

A delayed reaction to a Class K fire can mean damage to equipment, prolonged shutdowns, and serious safety risks. That’s why kitchens—whether in restaurants, hospitals, schools, or operating rooms with specialty cooking setups—need extinguishers and systems rated specifically for this fight class.

How These Letters Shape Safety Choices

Each of the fire extinguisher classes shapes a complete fire safety strategy. The classification system directly influences how facilities prepare, equip, and train for emergencies.

For starters, the placement of extinguishers depends entirely on the types of hazards present. A commercial kitchen needs Class K extinguishers near cooking stations, while a manufacturing plant dealing with flammable metals might require Class D units in very specific areas.

Offices or warehouses storing ordinary materials like paper, wood, or many plastics typically lean on ABC-rated models placed at designated intervals.

Inspection frequency is guided by risk

According to fire administration guidelines, high-risk areas may require more frequent checks—not just to meet compliance but to make sure your equipment is ready in real-world conditions.

Training is essential

Then there’s training. Knowing how to aim a solid stream is one thing, but knowing which extinguisher to grab and how to approach a Class B fuel fire or a Class K grease flare-up is another. Fire classification provides a framework for customized, practical safety education that actually sticks.

Even suppression system design, from restaurant hoods to industrial foam setups, relies on understanding what could burn and how to contain it. That’s why fire classes are foundational to building a safer, smarter space.

Conclusion

Knowing the difference between fire classes A, B, C, D, and K isn’t just technical—it’s practical. It helps you choose the right protection, respond with confidence, and stay ahead of the unexpected. And when you're ready to put that knowledge into action, we're here to help.

The Local Advantage: How Swartz Fire & Safety Helps You Get It Right

Fire safety should be customized, and that’s exactly where we come in. With over 35 years of experience protecting businesses across Central Pennsylvania, we know how to match the right tools to the real risks on-site.

Our services cover everything from portable fire extinguisher inspections and recharges to full installation and maintenance of kitchen suppression systems, vehicle-mounted extinguishers, and industrial fire protection. We also provide on-site training tailored to the actual fire classes your team may face.

Thanks to our fully equipped mobile service fleet, we bring everything directly to your door. That means inspections, recharges, and replacements can happen without interrupting your operations, whether you run a restaurant, a manufacturing facility, or manage a fleet of heavy equipment.

With deep technical training, field-tested knowledge, and a clear understanding of code and compliance, we’re here to make sure your fire safety plan isn’t just complete—it’s built for the way you work.

Let’s Make Sure You’re Covered

Every environment has its own fire risks, and the right protection starts with understanding what those are. From extinguisher placement and system design to inspections and training, we help you build a complete plan that fits how you operate.

Looking for a fire safety setup that works for your space? Get in touch today. We bring the equipment, expertise, and on-site service to help you stay ready.

Frequently Asked Questions

What are class ABCD and K fires?

They are categories of fires based on the material burning:

• A: ordinary combustibles
• B: flammable liquids
• C: energized electrical equipment
• D: combustible metals
• K: cooking oils and fats (mainly in commercial kitchens)

What are the ABCD types of fire?

They refer to different fire hazards:

• Class A – paper, wood, cloth
• Class B – gasoline, oil, solvents
• Class C – electrical systems
• Class D – metals like magnesium or titanium

What does ABCD mean on a fire extinguisher?

It means the extinguisher is rated to fight Class A, B, C, and D fires, each representing a different type of burning material.

Is a fire Class F or K?

They're the same. Class K is used in the U.S., while Class F is the European equivalent. Both cover fires involving cooking oils and fats.