What is a K Class Fire Extinguisher Used For?

Fire extinguishers are critical tools for stopping small fires before they spread, but it’s vital to use the correct type for each kind of fire. 

Using the wrong extinguisher can even make a fire worse.

Spraying water on a kitchen grease fire will only spread the flames. 

One particularly dangerous class of fire occurs in kitchens when cooking oils or fats overheat. 

These high-temperature grease fires. 

These are classified as Class K fires in the US, equivalent to Class F in the UK. 

They ignite suddenly and burn intensely. 

They require a special kind of extinguisher formulated specifically to handle burning oil and fat safely. 

This is where the Class K fire extinguisher comes into play: it is designed to tackle blazing cooking oils and keep a kitchen fire from turning into a disaster.

What is a K Class Fire Extinguisher Used For?

A Class K fire extinguisher is used for fires involving cooking oils, fats, and grease.

These are the types of fires that erupt in kitchens due to overheated oil. 

This extinguisher is specifically designed to combat blazing oil in deep fryers, frying pans, griddles, and other commercial cooking equipment. 

According to fire safety standards, a Class K extinguisher is the only effective means to safely put out fires fueled by vegetable oils, animal fats, or grease in cooking appliances.

What Makes a Class K Fire Extinguisher Unique

What makes the Class K extinguisher unique is its extinguishing agent. 

Unlike a water or dry powder extinguisher, a Class K unit contains a special wet chemical solution.

This is often potassium acetate or similar compounds. 

These chemical solutions are extremely effective on hot grease fires. 

When you discharge a Class K extinguisher onto burning oil, the wet chemical comes out as a fine mist and reacts with the fat. 

This reaction forms a thick, soapy foam blanket over the oil.

This process is called saponification. 

The foam smothers the flames by sealing off the oil from oxygen and also cools the oil below its ignition temperature, preventing the fire from reigniting.

Basically, the Class K extinguisher both starves the fire of oxygen and removes the heat, which are two essential elements needed for the fire to continue burning.

Why Can’t I Use a Different Fire Extinguisher on a K Class Fire?

You cannot substitute other types of fire extinguishers for a Class K fire because grease fires behave very differently from ordinary combustibles or flammable liquid fires. 

Fires involving cooking oil or fat require Class K extinguishers because no other extinguisher type can reliably or safely extinguish them. 

Using the wrong type can be ineffective or downright dangerous. 

Here’s why Class K fires need their own extinguisher and why other extinguishers won’t work:

Water Will Make a Grease Fire Worse

Never throw water on a burning pan of oil. 

Water is denser than oil, so it sinks below the burning grease and instantly turns into steam. 

As it evaporates, it expands to about 1,600 times its volume, erupting upward and carrying burning oil droplets with it. 

This causes the fire to explode and spread. 

Instead of cooling the fire, a splash of water can fling the flames to new areas (and possibly onto anyone nearby). 

Water and oil don’t mix, and using water will spread a Class K fire.

Standard Foam or Powder Extinguishers Aren’t Effective

Class B foam or dry powder extinguishers, which work for petrol or chemical fires, are not formulated for the extreme high-temperature conditions of cooking oil fires. 

Deep fryer oil can reach temperatures far above the ignition point of other flammable liquids.

A regular dry chemical extinguisher might knock down the flames briefly, but it does not cool the oil sufficiently. 

The oil can remain hot enough to reignite on its own a moment later.

This is essentially a ticking time bomb of fire. 

Also, dry chemical agents (like monoammonium phosphate powders) can form a crust on top of the oil that looks like it’s out, while underneath the oil is still burning or hot. 

When that crust is disturbed or if heat builds up again, the fire can flash back. 

Because they lack the cooling and smothering foam effect, normal Class B/C extinguishers often fail to prevent re-ignition of grease fires.

Co₂ (Carbon Dioxide) Extinguishers Aren’t Suitable

A CO₂ extinguisher fights fire by flooding the area with carbon dioxide to displace oxygen and cool the flames. 

However, with a Class K fire, CO₂ will only cool the surface of the oil while the deeper oil remains extremely hot. 

Once the CO₂ gas dissipates, the oxygen returns and the still-hot oil can reignite itself. 

Moreover, the high-pressure discharge from a CO₂ extinguisher can splatter the burning oil around, potentially spreading the fire to new areas. 

Thus, CO₂ might temporarily appear to put out a grease fire, but the fire is very likely to come roaring back.

How to Use a K Class Fire Extinguisher

If a cooking oil fire breaks out and it’s safe for you to attempt extinguishing it, you should follow proper steps to use the Class K fire extinguisher. 

Using this extinguisher is similar to using any portable extinguisher, but there are a few additional considerations for grease fires. 

Always remember the acronym PASS:

• Pull
• Aim
• Squeeze
• Sweep

This acronym outlines the basic steps for knowing how to use a fire extinguisher:

• Pull the safety pin out of the extinguisher’s handle. This pin prevents accidental discharge; pulling it will unlock the handle.

• Aim the nozzle or hose at the base of the fire, not at the flames. In a grease fire, that means aim where the oil is burning (the surface of the oil). You want to hit the burning oil directly with the extinguishing agent.

• Squeeze the handle slowly and evenly. This will start the flow of the wet chemical agent. Class K extinguishers are typically designed to discharge in a controlled, gentle spray to avoid splashing the oil.

• Sweep the nozzle from side to side across the base of the fire while continuing to aim at the oil. Cover the entire area that’s on fire with the mist, and keep spraying until the flames are completely out.

Keeping Safe

While performing these steps, maintain a safe distance. 

It’s recommended to start about 8 to 10 feet (roughly 3 metres) back from the fire and move forward carefully as the flames subside. 

Holding the extinguisher upright, direct the spray low and evenly over the burning oil. 

The wet chemical will create a foamy layer as it contacts the hot grease. 

Make sure to coat the whole surface of the burning oil with this foam. 

This ensures that the fire is fully smothered and cooled. 

Class K extinguishers are engineered to discharge at a lower pressure than other types precisely to avoid splattering the burning oil. 

However, a steady hand control is important to keep the spray directed where it’s needed.

As you fight the fire with the extinguisher, avoid getting too close to splattering grease and never attempt to carry a burning pan outside.

Let the extinguisher do the work of dousing the flames. 

Keep discharging the agent until you’re absolutely sure the fire is out. 

After Extinguishing the Fire

After the flames appear to be extinguished, watch the area closely for a minute or two in case of re-ignition. 

The wet chemical foam should prevent the oil from reigniting, but it’s wise to be vigilant. 

Once everything is under control, ventilate the area if possible. 

Remember to call the fire brigade or emergency services if the fire was significant or if there’s any doubt it might flare up again. 

Also, any used extinguisher will need to be recharged or replaced promptly.

Suppression Systems

If the kitchen has an automatic hood fire suppression system, activate that first or ensure it has activated before using the portable extinguisher. 

The hood system will release its own suppressing agent and often shut off the heat source to the cooking equipment. 

This reduces the intensity of the fire and prevents new fuel from feeding it, making it safer and more effective when you follow up with the handheld Class K extinguisher.

Where are K Class Fire Extinguishers Usually Found?

Class K fire extinguishers are typically found anywhere there is a significant risk of cooking oil or grease fires. 

This means they are most often located in commercial and institutional kitchens. 

These are some of the common places you’ll see Class K extinguishers installed and ready for use:

Restaurant and Café Kitchens

Restaurants, diners, cafeterias, and coffee shops with kitchens all contain cooking appliances that use oil or grease. 

Class K extinguishers are normally required in these kitchens, often positioned near deep fryers or grill areas.

Hotel and Catering Kitchens

Hotel restaurants, banquet hall kitchens, and catering companies prepare food on a large scale and usually have multiple high-temperature cooking stations. 

These sites will have Class K units handy in the cooking areas to address any fryer or skillet fires.

Food Trucks and Mobile Kitchens

Food trucks, street food stalls, and mobile catering vans often operate with compact deep fryers or woks in a tight space. 

A Class K extinguisher is crucial in these environments due to the elevated risk of grease fires in a confined area.

Institutional and Cafeteria Kitchens

Large kitchens in schools, universities, healthcare buildings, nursing homes, prisons, and other institutions commonly cook for many people using industrial-sized equipment. 

These facilities will have Class K extinguishers in the galley or kitchen area to meet fire codes and protect occupants.

Bakeries and Other Food Prep Facilities

Bakeries, pastry shops, or any food production facility that involves frying or high temperature oils will also keep a Class K extinguisher nearby. 

Any facility with commercial cooking equipment is likely to have one.

Key Takeaways

Class K fire extinguishers play a crucial role in kitchen safety. 

They are uniquely formulated to tackle the high-temperature oil and grease fires that frequently occur in cooking environments.

These are fires that other extinguishers simply cannot deal with safely. 

Statistics show that a large share of fires in restaurants and cafes start in the kitchen, where hot cooking equipment can ignite oils and fats. 

Having a Class K extinguisher on the premises (and knowing how to use it) is therefore an essential safeguard for anyone who operates commercial cooking equipment.

A Class K fire extinguisher is a kitchen’s best defense against one of its most perilous fire hazards, and ensures that a fire doesn’t turn into a tragedy.