What’s Inside? A Guide to Fire Extinguisher Chemicals

Introduction

Before disposing of or discharging a fire extinguisher, it’s helpful to know what chemicals are inside and how to handle them. Different types of fire extinguishers contain specific agents tailored to various fire classes. Here’s a quick guide to help you understand what’s inside each type and how to handle them safely.

Dry Chemical (Class A, B, C)

These are among the most common types of fire extinguishers as they are your all-around use units. They typically contain dry chemical powders like monoammonium phosphate or sodium bicarbonate, which can handle fires involving ordinary combustibles, flammable liquids, and electrical equipment. You can safely discharge this outdoors, but it’s best to avoid breathing in the powder, as it can be irritating.

We recommend aiming the nozzle into a large garbage bag, squeezing the handle once or twice, and waiting 24 hours for the rest of the internal pressure to leak out on its own. Once used any fire extinguisher will slowly leak pressure until they are empty. You can’t use and re-use extinguishers over any length of time.

Carbon Dioxide (Class B, C)

CO2 extinguishers are designed to combat fires in electrical equipment and flammable liquids. They work by displacing oxygen, which smothers the fire. CO2 extinguishers are safe to discharge outside, but avoid using them in enclosed spaces without ventilation, as the gas can displace oxygen, creating a suffocation risk.

Water Extinguishers (Class A)

Water extinguishers contain only water, making them completely safe to discharge outside. However, they’re only suitable for Class A fires (ordinary combustibles) and should never be used on electrical or grease fires, as water can conduct electricity and spread flammable liquids. They are most seen in large silver/aluminum cylinders.

Kitchen Extinguishers (Class K)

Class K extinguishers are specially designed to handle kitchen fires, which often involve cooking oils and fats. They contain wet chemical agents, typically potassium acetate, which works by cooling and forming a foam blanket over the hot oil, preventing re-ignition. While these chemicals are not particularly toxic, they can be greasy and tricky to clean up.
These also come in large silver/aluminum cylinders, so be very careful to make sure you don’t get it mixed up with a Water Extinguisher. Using the wrong type of extinguisher will spread the fire and make things much worse. Because of their unique purpose, it’s best to avoid discharging them unnecessarily. For disposal, check with a local hazardous waste facility or your nearest Encore Fire Protection location to ensure proper handling.

Combustible Metals (Class D)

Class D extinguishers are specialized for metal fires involving reactive metals like magnesium, sodium, aluminum, or titanium. These extinguishers typically contain a dry powder, such as sodium chloride or copper-based compounds, designed to isolate the fire and absorb heat. Class D extinguishers are unique in that they are used specifically for combustible metal fires and are not suitable for other fire types.

Handling a Class D extinguisher requires extra caution. It’s best not to discharge these extinguishers unless you’re responding to a specific metal fire. If you are in need to use one of these units, please read the instructions for use prior to discharge. This type is designed to smother the fire by first creating a ring of powder around the outside of the fire to stop the spread and then slowly covering the circle with powder to cover up the burning material. Just spraying the chemical straight on to the fire will not extinguish the fire and is a waste of the chemical.

If you have one that requires disposal, contact a professional hazardous waste service, as the chemicals inside are tailored to a specific use and can be harmful if not handled correctly. Your local Encore Fire Protection location can help direct you to appropriate disposal options.

Here is a quick reference chart.

Encore Fire Protection Can Help
This list covers the most common fire extinguisher but is not an exhaustive list. If you’re unsure of your extinguisher’s type/contents, the proper situation to use one, or need assistance with safe disposal, contact Encore Fire Protection. Our team can help you identify the type of extinguisher you have and provide guidance on safe disposal options. We also offer services for recharging and replacing fire extinguishers, so you can always stay prepared.