Fire Extinguishers: Everything Car People Need to Know

There are only a few things that should keep owners of vintage cars up at night, and fire is near the top of the list. Our beloved vehicles are composed of many flammable components—interior fabrics, plastic trim, and rubber seals,—and that is before we take into account the gallons of flammable fuel that we pump into them and hope to burn only in the most controlled manner. Fire is scary, and should be, but a small amount of preparation can help ease the worry and prevent disaster.

Let’s take a look at what fire extinguishers are, what’s inside them, and how to pick the right one for your shop or car.

A Quick History

Like many automotive items, the concept of a fire extinguisher traces back much further than you might think. To understand how to fight fire, we first need to think about the fire itself. The fire triangle has been understood for most of human history: Fuel, oxygen, and heat. Combining these three things enabled humans to cook food, illuminate and heat living spaces, and even forge materials. The utility of fire is immense, as is its destructive power. Hence the various methods of containing and extinguishing fires.

Thousands of years ago, people used simple hand pumps to squirt water at flames in the hopes of cooling the burning material below ignition point while smothering the fire by removing the oxygen. A better understanding of how fires worked enabled new methods and techniques of fighting fire. In the early 1800s, Captain George William Manby created the first modern fire extinguisher by putting three pounds of potassium carbonate into a copper vessel and pressurizing it with air. A simple valve released the pressure and sprayed the dry chemical onto the fire.

Iterations of those designs are still in use today. Modern extinguishers all function similar to Manby’s—by controlled release of a pressurized substance—but the contents of the canisters have evolved significantly over the years. Today, the various types and uses have been narrowed down to just a handful of options that cover the vast majority of consumer needs, including those of car enthusiasts like you and me.

“The most common sources of vehicle fires are electrical failure or structure fire. A smaller percentage start from collisions or wildfires,” said Michelle Gourley, assistant manager of Hagerty’s Claims team.

Gourley also said that the typical structure fire starts with lighting or electrical failure and that battery maintainers are a common culprit. Batteries can also be removed and charged away from combustible materials, and battery disconnect switches are a cheap, easy-to-install way to minimize the amount of charging needed. Speaking of storage, removing and properly storing or disposing of flammable materials (and the rags soaked in them) are other important safety steps that can prevent the need for fire extinguishers.

Classifications, Sizing, and Types

Fire extinguishers are broken down into five categories based on the type of agent they contain and the situation they are designed to handle. Using the appropriate type is critical to effectively putting out a fire. We’ll get to agents in a moment, but here is a quick look at the five classes that you are likely to encounter, and what type of fire they are designed to handle:

Class A: Fires in ordinary combustible materials, such as wood, cloth, paper, rubber, and many plastics

Class B: Fires in flammable liquids, combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols, and flammable gases

Class C: Fires that involve energized electrical equipment

Class D: Fires in combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium

Class K: Fires in cooking appliances that involve combustible cooking media (vegetable or animal oils and fats)

Sizing

In addition to the letter rating system, some extinguishers also have a numerical rating that can help users determine the size of fire that a given extinguisher can control.

Class A extinguishers are rated by water equivalency, where each number represents 1 ¼ gallons of water. As an example, 2A means the extinguisher is just as effective as 2 ½ gallons of water. A 4A is equivalent to 5 gallons of water.

Class B extinguishers are rated by the square footage they can cover. 20B means that if the nozzle is swept side to side in proper form, there is enough extinguishing agent to handle 20 square feet of coverage.

Class C and D do not carry a size rating. A Class C electrical fire is simply a Class A or Class B fire with energized components. To put it out, you must use a non-conductive extinguishing medium to prevent electricity from conducting back to the extinguisher (and you). To effectively fight Class C fires, choose based on the Class A and Class B size ratings. The effectiveness of a Class D extinguisher is detailed on the nameplate and is based on the specific combustible metal for which the extinguisher is recommended.

Agent Type

The final thing to consider in selecting an extinguisher is the composition of the fire-fighting agent. Most extinguishers are little more than a pressurized can containing a chemical designed to smother the fire. When the user pulls the safety pin and opens the valve, the chemical agent is drawn up a siphon tube and spread by a nozzle. This is why it is important to hold an extinguisher vertically; otherwise, the agent could shift and not be drawn up the siphon tube, rendering the extinguisher useless.

While many of the canisters might appear the same, what is inside them matters—not only when a fire breaks out, but after it’s extinguished, when you’re cleaning up. The label on an extinguisher will detail its contents, so here’s what you need to know to pick the right one.

Dry Chemical
Dry chemical agents come in multiple forms and are also often the most effective at putting out fires, though they can have downsides. Three of the most popular are sodium bicarbonate, ammonium phosphate, and potassium bicarbonate. Sodium bicarbonate is non-toxic, non-conductive, and non-corrosive. It is easy to clean up with a vacuum or broom, or by flushing with water.

The second is mono ammonium phosphate. It is non-conductive but can be mildly corrosive when combined with moisture. In order to avoid corrosion, it is necessary to scrub and thoroughly clean up the contacted area once the fire is extinguished to prevent further damage.

A third option is potassium bicarbonate. Like sodium bicarbonate, it is non-conductive and non-corrosive, with an easy clean-up procedure of vacuuming, sweeping, or flushing with water.

Carbon Dioxide
Carbon dioxide breaks the fire triangle by displacing the oxygen to stop a fire. Carbon dioxide is environmentally friendly and leaves no residue, making it an attractive choice where minimizing collateral damage or contamination is key, but CO2 extinguishers are less effective than other options due to their limited range.

Halotron or Halon
Halon is a vaporizing liquid that leaves no residue, making it perfect for sensitive areas where leaving no residue is a priority. It is the opposite of ozone-friendly, however. Halon has been out of production since 1994 because it contains bromine, which is 40–100 times more effective at destroying ozone than chlorine, according to the National Oceanic and Atmospheric Administration. To figure out why these types of extinguishers are still available, we reached out to H3R Performance, which sells both halon and halotron extinguishers. The company clarified that it does not make new halon but rather recycles it. (The availability of halon is similar to that of R12. Older air conditioning systems that use R12 can still be serviced and used, but only by using recycled refrigerant.) Halon is also the standard for use in aircraft.

Foam
Foam floats on flammable liquids to tame the fire and prevent reflashes. To clean the affected area, the foam must be washed away and left to evaporate.

Water
The most common agent is water; however, it cannot be used for class B or C fires because it is conductive.

Wet chemical fire extinguishers (Class K)
The potassium acetate–based agent discharges as a fine mist, which forms a soapy foam that suppresses any vapors and steam, reducing the risk of re-ignition while smothering the flames. Class K fire extinguishers are typically found in commercial cooking areas.

Solid chemical

In recent history, other non-traditional methods of extinguishers have appeared that rely on a chemical reaction to produce an extended jet of nitrogen and potassium. Examples of this technology, such as the product from Element, cut off the supply of oxygen to the fire but often require the user to be closer to the point of ignition than other methods. That said, they are safe to store and maintenance-free for relatively long periods of time.

What to Buy and Where to Put It

Looking through these types, it is easy to see why many popular and readily available options carry a triple rating—for example, a single type of extinguisher might cover A, B, and C combustible events. All of those risks are present in most garages, so, at minimum, whatever extinguisher is mounted to the wall of a home garage should carry those three ratings and be as large as your budget and storage space will allow.

Placement is also critical. Most home garages are small enough that having line-of-sight access to the extinguisher is enough, but for larger spaces, you may need more than one. The distance that you must travel to get to each one matters, too. Thankfully, the National Fire Protection Association has a handy chart to help you:

UL Rating

More important than anything is the knowledge that a fire extinguisher will work as you expect in the moment you need it to. That is why it is important to always purchase a product (whether for automotive, garage, or home use) rated by Underwriters Laboratories (UL). A manufacturer may spend over $100,000 for UL to test its fire extinguisher, and that testing, and the label that follows a successful one, confirms you are indeed purchasing what is being advertised and can expect it to function as designed. All UL-rated fire extinguishers include a bracket for mounting to a wall or a safe place in a vehicle.

We cannot entirely eliminate the risk of fire, and therefore, it is best to be prepared for the worst. Selecting, purchasing, and installing a proper fire extinguisher is not the most fun task compared to buying performance parts or new tools, but when spark turns to flame, the clock moves quickly. It’s said an ounce of prevention is worth a pound of cure, and a well-placed, ready fire extinguisher is an even stronger value proposition—it could be worth as much as your car.