Occupational Health & Safety

Emergency Response

The ABCs of Inspecting Dry Chemical Fire Extinguishers

By Don Frank · April 2008

An improperly maintained or under-weight extinguisher can seriously endanger life and property.

When performing an inspection at a business, you should inspect its fire extinguishers. Looking at the psi gauge to see whether the arrow is in the green and inspecting the tag to determine whether it is current or the extinguisher needs to be inspected will tell you some things about it, but there is a bit more you should know.

The basic operation of the stored pressure extinguisher is this: It contains in a low pressure cylinder the expellant gas, usually nitrogen, and the ABC or BC chemical. When the pin is removed from the top handle and the handle pressed downward against the bottom carrying handle, the valve stem moves downward in the valve head and the agent is released under pressure through a siphon tube, up past the compression spring and past the valve stem and valve head, out through the hose and nozzle or nozzle.

Getting Started
The inspection should start with a visual inspection. Look for signs of damage, welding, or any type of modification made to the extinguisher; that the valve head assembly is not damaged; handles are not missing (as shown in Photo 1) or damaged; the pull pin is located in the handle with the tamper seal holding the pin in place; it has no wire, wire tie, or tape holding the pin in place; and the pressure gauge arrow is in the proper operating range (usually in the “green” area of the gauge). You should able to read the pressure gauge, and it should not be faded (Photo 1). You should check the nozzle/nozzle and hose for damage and weather cracks, that the orifice is free from obstruction, and the instruction-name plate is legible (Photo 1) and attached to the fire extinguisher cylinder; which will tell you about other important factors of the fire extinguisher that will be discussed here.

Reading the information on the labels will tell you all about the fire extinguisher and how to operate it. The letters and pictures indicating the classes of fires it is capable of extinguishing should appear only on the front of the extinguisher; nothing else should be placed on the front to distract from the information. The rating number that indicates the extinguishing capability, information on how much dry chemical should be in the fire extinguisher, and the suitable temperatures in which the agent will operate are on the label, as shown in the Photos 2, 2a, and 2b below.

The manufacture date will tell you two important items about the fire extinguisher you are inspecting.The date is found in one of three places: on the label, stamped on the bottom outside edge of the cylinder, or stamped to the underside of the extinguisher. Some companies place a sticker showing the date of manufacture.

This date is important because every five years (for extinguishers carried in vehicles) or 12 years (for those not carried in vehicles, i.e., at businesses) from the date of manufacture or from the last “hydro” sticker test date, the fire extinguisher cylinder is to be hydrostatically tested (“hydro tested”), as shown in Photo 4.

Hydrostatic testing and the yearly fire hose testing are basically the same; the fire extinguisher cylinder is pressurized under water pressure at test pressure. Photo 4 shows a modified out of jacket test performed. If the cylinder passed the hydro test, the inside cylinder is dried by hot air on a drying rack before it is reassembled and a hydro sticker is placed on the fire extinguisher cylinder (Photo 5).

There are two types of hydrostatic test stickers (Photo 6) that you may see: 1) non- DOT cylinder, three times the gauge pressure or to the manufacturer’s recommendation on the label, the pressure, year, and month the test was performed, 2) DOT cylinder, which displays a “RIN” retested identification number sticker, the cylinder tested to twice the gauge pressure or to the manufacturer’s recommendation, month and year the test was performed. All test information will be on the label.

The California State Fire Marshal in 2003 implemented the “six year tear down policy.” Any fire extinguisher before 2003 would have the internal maintenance conducted, powder emptied, all parts cleaned, and the extinguisher properly reassembled. After completion of the work, a verification of service collar (VSC) would be affixed when placing the valve head assembly into the cylinder to show that service was performed and the date, month, and by whom. (Photo 7)

The next tear down would be in six years. Any fire extinguisher 2003 or newer would not have this VSC unless service was performed before its “six year tear down.”

The Importance of the Gross Weight Check
The last check of the fire extinguisher, and one that is mostly overlooked and very important, is the gross weight check. Looking on the label, you will find the maintenance/recharge instructions; it will tell you how many pounds of dry chemical to put into the fire extinguisher and the psi at which to pressurize the cylinder. Compare label psi to what is on the gauge, because this will tell you if it has the proper gauge for that pressure. If it does have a wrong gauge, this will affect the discharge and rating of the fire extinguisher.

Check the gross weight with pin and tamper seal in place and the valve head, including hose and nozzle or nozzle. Proper hose and nozzle or nozzle as outlined on the label must be correct, for this, too, will affect the rating of the fire extinguisher if it is wrong. Fire extinguishers will have in writing the weight (gross) of the total fire extinguisher or the parameters to follow. For example, a 5 pound ABC extinguisher will say on the label, “Fill with 5 pounds of ABC chemical . . . gross weight of 8 lbs. 5oz. ± 8 oz.”

If you weigh this fire extinguisher, it should not be below 7 pounds, 14 ounces. A fire extinguisher below the minimal weight can only happen when the person who was refilling the extinguisher did not bother letting the chemical settle in the cylinder and then topping it off with added chemical, did not have a scale, or did not use a scale while doing the maintenance. One cannot know what the actual weight of the extinguisher is without a scale; just by hefting the extinguisher, your brain cannot tell you whether it is at the proper weight—only whether it is heavy or light.

If it is below the minimum amount allowed as stated on the label, this will once again affect the rating of the fire extinguisher. (Photo 8)

Remember, all fire extinguisher labels will instruct you: 1) to fill with proper amount of chemical in pounds, and 2) what the total gross weight should be of that particular fire extinguisher. If you do come across a fire extinguisher with a deficiency during your inspection, remove it from service and replace it with another extinguisher in its place until the deficiency is corrected. The fire extinguisher is a very effective tool to extinguish a fire before it gets out of hand and endangers life or property, but an extinguisher not properly maintained or under weight can cause serious danger to life and property. On your next fire inspection, check out those other items to make sure the people that are counting on us know we do care for their safety and are getting the proper service they are paying for from a fire extinguisher company.

About the author

Don Frank
Don Frank retired from the fire service after 29 years. He is a fire service instructor and provides contract fire services. He served as a firefighter with the Defense Distribution Depot, San Joaquin, Calif. (DDJC), as a rescue firefighter with the Robins Air Force Base Fire Department in Georgia, as a rescue/EMT at McClellan Air Force Base in Sacramento, and with the Springlake (CA) Fire Protection District. He is an instructor in all phases of aircraft emergency firefighting, confined space, high-angle rescue, and building collapse operations. A nationally certified fire instructor III, he holds fire officer certifications from California and the U.S. Department of Defense.