Portable Fire Extinguishers: A Brief Introduction

What are portable fire extinguishers?

Put simply, portable fire extinguishers are tools used to put out small fires when they occur. You've surely seen them around, but do you know how they work or how to use them?

Most portable fire extinguishers you see in buildings today are stored-pressure dry chemical type, but others exist and are separated by a classification which specifies what sort of fire they're designed to put out.  There are five main types:

• Class A extinguishers are meant for use on flammable and combustible solids, like wood, textiles, paper, fabric, etc.  The most common extinguisher of this type is the water extinguisher.
• Water extinguishes fire by cooling it and the adjacent solids on which the fire feeds.
• Class B extinguishers are meant to put out flammable and combustible liquids like oil, gasoline, and diesel.  The most common extinguishers of this type are foam or sodium bicarbonate extinguishers.
• Foam and sodium bicarbonate serve to extinguish the fire by suffocating it - that is, depriving it of the oxygen fire needs to survive.
• Class C extinguishers are meant to put out small electrical fires, where spraying water onto the fire would only serve to aggravate the problem. The most common types are carbon dioxide, halogenated agent, and dry chemical.
• Carbon dioxide and halogenated agents also suffocate fire, by displacing oxygen.
• Class D extinguishers are meant for flammable metals like magnesium, sodium, or lithium.  Water does not put out these sorts of fires and in fact only makes the fire worse.  Extinguishers of this type use dry powder.
• The dry powder used in class D extinguishers also serves to remove the oxygen from the fire.
• Class K extinguishers are meant for kitchen fires. Kitchen fires are most often caused by grease, which is in and of itself a Class B fire, but in these cases, dumping foam or baking soda onto a hot griddle or into a deep fryer is not always the best option as burning grease burns too hot for a regular Class B extinguisher to be effective.
• Extinguishers of this type use wet chemical which saponifies (forming a sort of soapy layer) over the burning grease, thus snuffing out the fire.

Combination Extinguishers

Many fire extinguishers today are suitable for multiple purposes. By far the most common portable fire extinguisher you will see in buildings and homes is the type ABC extinguisher.  It's called this because it can handle class A, class B, and class C fires.  The agent inside, monoammonium phosphate, is a yellowish powder that puts out the fire by interrupting the chemical chain reaction on which the fire survives.

Fire Extinguisher Tips

• Be sure to buy the right type of extinguisher for your application.  For general use around the house, a household ABC extinguisher is a great option. For the automobile, a type BC extinguisher is a good fit.  Like household type ABC extinguishers, Type BC automotive extinguishers can be found at any home improvement store.
• Visually inspect your fire extinguisher monthly. Check to make sure the pin is in place, the gauge reads full, and the fire extinguisher feels full.
• NFPA requires fire extinguishers to be hydrostatically tested every twelve years. Since most household fire extinguishers aren't designed to be hydrostatically tested, replace your fire extinguisher if it is over ten years old.