Q&A for How to Refill a Fire Extinguisher

Take it to a professional. Unless it is a water-filled extinguisher with air pressure, it's unlikely you will have the necessary inert gas and equipment to re-pressurize any fire extinguisher. Many use nitrogen gas. Some use carbon dioxide cylinders (usually in commercial or industrial use).

Yes, unless the extinguisher is water-based and uses air pressure (e.g., from an air compressor), it is generally impossible for an ordinary person without special equipment and training to repressurize an extinguisher safely. Get a new one or have it professionally refilled.

The ratio in this instance is 1:2 water and foam.

You would need to ask them first. Many departments are no longer equipped or staffed for handling refills of anything other than water-based extinguishers (air-pressurized water, or APW). There may also be "municipal liability" if they do it improperly.

You typically use a hand pump or a compressed air source. Hand pumps are manual devices that you pump to pressurize the extinguisher. Compressed air sources can include nitrogen cylinders or air compressors equipped with the appropriate fittings to connect to an extinguisher's valve. These methods ensure the extinguisher is properly pressurized and ready for use in case of fire.

Refilling a carbon dioxide (CO₂) fire extinguisher should only be performed by certified professionals. The process involves depressurizing the extinguisher, inspecting it for damage, and then refilling it with liquid CO₂ using specialized high-pressure machines. Afterward, the extinguisher is weighed and leak-tested to confirm its safety and functionality.

You cannot safely re-pressurize a CO₂ fire extinguisher with a bicycle pump for its intended firefighting purpose, as it requires special high-pressure equipment and CO₂. However, you can repurpose old, completely empty, and depressurized extinguishers into DIY water sprayers by fitting a valve and using a bicycle pump for low air pressure. This repurposing is only for light tasks like gardening and not for fire protection, as it will no longer function as a proper fire extinguisher.

The standard ratio is 1 part foam concentrate to 9 parts water. For example, if you use 9 liters of foam concentrate, you would mix it with 81 liters of water. Always check the manufacturer's instructions on the label, as some concentrates may have slightly different recommended dilutions.

You should fill the propellant gas (typically nitrogen or compressed air) in a 3.3-liter fire extinguisher to the manufacturer-specified working pressure. This is usually around 12–15 bar (approximately 175–220 psi) for small portable extinguishers.