ABCDs of Fire Extinguishers
Dependability is the most important quality that every portable fire extinguisher must have. An extinguisher rated for class B and C Fires will sometimes put out a class A fire—if it works.
The way to ensure continuance of the dependability built into an extinguisher by the manufacturer is to conduct an effective maintenance program. Whether extinguishers are on fire apparatus or in buildings, they should be inspected frequently and maintained regularly.
Inspections are quick, superficial checkups while maintenance is a thorough investigation of the working and non-working parts that will provide an accurate evaluation of an extinguisher’s condition and possible need for repair.
How often inspections should be conducted depends on the location and use of extinguishers. For example, extinguishers on fire apparatus should be inspected daily, but monthly inspections should be sufficient in office buildings and apartment houses. On the other hand, extinguishers in an industrial plant should be inspected every time they are taken to a location for fire watch duty.
Inspecting by lifting
Hefting extinguishers is one way of inspecting every type. With experience, a man learns to estimate whether the proper amount of extinguishing agent is present. With a 15-pound carbon dioxide or a 2 1/2-gallon soda-acid extinguisher, the difference in weight between a charged and an expended extinguisher is readily apparent.
A broken seal or tamper indicator will show the need for further inspection to determine whether any of the extinguishing agent has been expelled. Incidentally, tamper indicators should be applied loosely enough for the extinguisher to be lifted slightly off its hook to get a feel of its weight. Extinguishers that are not properly in place should be suspect and thoroughly checked for any damage and the amount of extinguishing agent and pressurizing capability.
A quick check also can spot any leakage or corrosion and whether the nozzle and hose or horn are in good condition. A glance at a nozzle or horn also can sometimes spot a clogged condition.
If the inspector has difficulty spotting the location of an extinguisher, then the extinguisher should be relocated, or if something has been placed in front of the extinguisher, then the concealing material must be moved.
An extinguisher location that was easily visible can be obscured for all practical purposes by the installation of machinery several feet away. Although signs are sometimes used to indicate an extinguisher location, it is usually better to move the extinguisher to an easily visible spot.
Use your eyes
As you can see, most “inspecting” is done by merely using your eyes. Gages on stored pressure type extinguishers should be read along with the dates on maintenance tags. Anything ususual about an extinguisher, such as a dent or scraped paint, should be noticed. These things, among others, may indicate that an extinguisher has been dropped and should be completely checked, including a hydrostatic test to determine if the cylinder is still serviceable.
The pressurized and pump-type water extinguishers on fire apparatus should be tested at least once a week by squirting a little water. Daily checks include reading the pressure gage on the first type and removing the tank cover to determine the water level in the other type. The pressurized water type extinguisher is so easy to recharge that by now it should have replaced all soda acid units on fire apparatus.
Again because of recharging ease, the dry chemical extinguisher most suitable for fire apparatus is the type pressurized by a cartridge of carbon dioxide or nitrogen. There is no pressure in the cylinder containing the dry chemical until the operator presses a plunger to rupture the disk seal of the gas cartridge. Therefore, the cylinder cap can be unscrewed to inspect the level of the dry chemical.
Gas cartridge checkup
At the same time, the gas cartridge can be unscrewed (it has a left-hand thread) from the connection to the cylinder to determine whether the cartridge seal is intact. A filled weight is stamped on the metal gas cartridge and the cartridge should be weighed to make certain that it is within 10 percent of the specified weight. Before a replacement cartridge is installed, it should be weighed to make certain that there has been no leakage around the rupture-disk seal. In structural service, these cartridges should be weighed every six months, but in the fire service, they should be weighed monthly.
Whether the dry chemical used is sodium bicarbonate, potassium bicarbonate or the multipurpose ABC formulation, primarily an ammonium-phosphate base, refilling should be done with a large funnel in the open or in an area where the dispersal of the fine particles in the atmosphere will not be objectionable from a cleanup standpoint. A particularly useful funnel for filling 20 and 30-pound dry chemical extinguishers can be obtained by buying a metal shade primarily used for electric lights in factories. The hole is sufficiently large and there is enough of a bowl shape to the shade to funnel the dry chemical into the extinguisher as you scoop it out of a 50-pound of larger shipping container. A large scoop, about 8 inches long, can be bought in hardware or restaurant supply stores.
In the fire service, dry chemical extinguishers that have been used still have a considerable amount of agent left. To save this dry chemical for further use, turn the extinguisher upside down and crack the discharge valve to bleed off the pressure slowly. This should be done outside where the slight amount of dry chemical that comes out of the nozzle will be unobjectionable, or the nozzle can be directed into a large trash can indoors. Refilling a dry chemical extinguisher also can be done outside to eliminate the inevitable cleanup that must follow even carful handling of the material indoors.
Now for a word of warning. Using multipurpose ammonium phosphatebase extinguishing agent in a dry chemical extinguisher that contained sodium bicarbonate or potassium bicarbonate can be dangerous unless it is certain that the extinguisher has been completely cleaned of the sodium or potassium bicarbonate. A chemical reaction developing enough pressure to rupture a cylinder could be the result of mixing an ABC dry chemical formulation with sodium or potassium bicarbonate.
Carbon dioxide units
CO2 extinguishers are weighed to determine whether they are fully charged. Each extinguisher has its weight stamped on it. Some of the old extinguishers have only the fully charged weight stamped on the valve housing. On others, weight information stamped on the cylinder plate states the empty weight of the cylinder, hose and horn, the weight of the CO2 charge and the total weight of the fully charged extinguisher.
Low platform scales, such as standard 50-pound capacity parcel post scales available in stationery stores, provide a convenient facility for checking the weights of the 15-pound carbon dioxide extinguishers usually found in the fire service. The size of CO2 extinguishers is defined by the weight of the charge, and these extinguishers are regarded as acceptable for use as long as the actual weight of the CO2 charge is not more than 10 percent less than the designated weight. For example, a 15-pound CO2 extinguisher need not be recharged as long as its total weight is not more than 1.5 pounds below the specified fully charged total weight.
Unless a fire department uses a large number of CO2 extinguishers, it is more practical to have these extinguishers recharged by a private contractor.
Pressurized water extinguishers are filled to the bottom of the tube that extends into the cylinder from the top opening. This leaves an air space for the introduction of compressed air. An easy way to fill to the proper level is to let the water rapidly come right up to the top of the cylinder and then shake the cylinder gently. This will expel some of the air trapped between the tube and the cylinder wall, and the water will fall to the bottom of the tube. The extinguisher will have the right amount of water in it.
After screwing the valve and discharge tube assembly to the cylinder, use a compressed air hose to bring the pressure up to about 125 psi for 2 1/2-gallon extinguishers. The compressor air tank pressure should be at least 140 psi to avoid a situation in which the compressor tank and extinguisher pressures equalize. If they do, then water will flow from the extinguisher into the air hose.
One of the problems in recharging pressurized dry chemical extinguishers is making certain that no dry chemical particles remain on the valve seat. This prevents proper seating of the valve with the result that there will be a pressure leak. The 2 1/2-pound dry chemical extinguishers seem to be particularly prone to this problem. Once a leak occurs, the only remedy is to bleed off what is left of the pressure by inverting the extinguisher and cracking the valve in order to clean off the valve seat and repressurize.
All extinguishers should be hydrostatically tested. The recommended test period is every five years for the following types of extinguishers: pressurized water, carbon dioxide, dry chemical with stainless steel, aluminum or soldered brass shells, soda acid, cartridge-operated water, loaded stream and foam.
A 12-year test interval is recommended for the following types of extinguishers: dry chemical with brazed brass or mild stell shells, dry powder with mild steel shells, and bromotrifluoromethane (FE 1301).
The Department of Transportation has its own requirements for DOT cylinders.
Dry powder extinguishing agents are for use on certain metals, class D fires. The agent may be applied by a scoop or shovel or with an extinguisher. It is necessary to select the proper extinguishing agent for the metal to be protected as no single agent is regarded as suitable for extinguishing all burning metals.
Extinguishers that receive a B-C rating from Underwriters’ Laboratories receive a numeral in front of the B to indicate their relative effectiveness through testing with fires in different size pans of flammable liquids. However, the C rating indicates only that the extinguishing agent will not increase the conductivity of electricity through a 10-inch air gap, and no extinguisher receives a C rating unless it has a class A or B rating, or both.