Keep Your Powder Dry
IT is very likely that ten years ago a group such as this would have been but little interested in listening to a discussion of dry chemical fire extinguishers. At that time there were less than 10,000 dry chemical fire extinguishers of all makes and sizes. At the present time there are nearly half a million dry chemical fire extinguishers in use. In addition, dry chemical piped systems have been installed in industrial plants and pipe line pumping stations, and fire trucks containing up to 4,000 lb. of dry chemical have been constructed. In 1941 there was only one manufacturer of approved dry chemical fire extinguishers and now there are at least eight manufacturers of Underwriters’ Laboratories approved dry chemical fire extinguishers. Most of this activity in dry chemical fire extinguishing equipment has taken place in the past four years and apparently the use of this type of equipment will continue to increase rapidly in the future.
As you know, dry chemical is composed primarily of sodium bicarbonate (baking soda) thoroughly mixed with other materials to make the sodium bicarbonate moisture repellant, resistant to caking, and free-flowing. The earliest use of sodium bicarbonate as a fire extinguishing agent was in tubes. The first mention of this material in tubes in published fire protection literature followed the Iroquois Theatre fire in 1903 in which 600 lives were lost. An investigation after the fire showed that one of the stage hands had attempted to use a tube of sodium bicarbonate and had failed to control the fire. Underwriters’ Laboratories, Inc., made tests of the tubes and found that they contained primarily sodium bicarbonate with iron oxide, chalk, sand, clay, talc, or starch added to prevent caking but that none contained water repellancy agents. Out of 31 tubes over four years oid, the Underwriters’ Laboratories found that 11 were caked sufficiently to prevent use.
The Germans developed a gas-pressure type dry chemical fire extinguisher called the “Total” which used a dry chemical consisting primarily of sodium bicarbonate but also containing about 15% of borax and mixed with water-repeliancy agents. The borax included in the German dry chemical was supposed to melt on striking a hot surface and to form a protective coating over materials such as wood, but the value of the borax coating is highly debatable.
The first gas-pressure type dry chemical fire extinguisher manufactured and sold in the United States was made in about 1928. This extinguisher had a carbon dioxide cartridge outside of the dry chemical container and was a distinct improvement over the German model because the American unit was equipped-with a hose and with a nozzle which permitted control of the flow of dry chemical.
The pictures show the various models produced and the approximate year in which they were first sold. No attempt is made to show every size and make produced in the 1930’s but it will be noticed that all of these extinguishers had the carbon dioxide cartridge located within the dry chemical container and all used a hose and shut-off nozzle. Also, all of these extinguishers were filled through the bottom opening, the mechanism for releasing the carbon dioxide which expelled the dry chemical being an integral part of the head ring of the extinguisher.
In 1943 the first major improvements in dry chemical were made. Among other changes in the dry chemical, the size of the particles was reduced. This change in the dry chemical resulted in an increased effectiveness amounting to about 50% when measured in terms of the areas of gasoline fires in steel-sided test pans which could be extinguished.
In 1944 a new type of dry chemical fire extinguisher was introduced. This extinguisher resembled in many respects the first gas-pressure type dry chemical fire extinguisher produced (in 1928) in that the carbon dioxide cartridge was outside of the dry chemical container, the unit was equipped with a hose with shut-off nozzle, and the dry chemical was charged into the extinguisher through the top.
This illustration and the others showing the various types of dry chemical fire extinguishers produced in the later years indicate not only the approximate time in which these units were put on the market but also show all sizes and makes.
In 1946 another new design of dry chemical fire extinguisher was brought out. These units differed from previous models in the nozzle design and in the use of a removable cartridge guard, the cartridge on this extinguisher also being outside of the dry chemical container. These units also differed from previous dry chemical units with the cartridges outside in that the carbon dioxide was released from the cartridges by puncturing the seals instead of opening valves. The nozzle differed from previous designs in that a lower velocity, wider, stream of dry chemical was produced which is claimed to require less technique on the part of the operator than did the higher velocity, more narrow streams of the older types of dry chemical extinguishers.
In 1947, two new dry chemical extinguishers were brought on the market, both by the same two manufacturers whose extinguishers were produced in the 1940’s. These extinguishers were in 4-lb. and 10-lb. capacity, the first units of these capacities produced in the United States. The 4-lb. unit has the cartridge inside of the dry chemical container, is filled through the top, and the discharge nozzle is at the bottom, no hose being used. The 10-lb. unit is a smaller version of the extinguisher produced in 1944. In 1948, three new dry chemical extinguishers were produced by manufacturers new to the dry chemical field. These units were in 5, 10. and 25-lb. capacities. The 5-lb. and 10-lb. units resemble the 4-lb. unit produced in 1948 but are filled through the bottom, the nozzle assembly being removable from the shell. The 25-lb. unit is radically different from any earlier dry chemical extinguishers in having the cartridge at the top of unit, attached to the fill cap. The carbon dioxide is released to the dry chemical chamber by a valve operated by a thumb lever.
In 1949. the largest number of new types of dry chemical extinguishers ever brought out in one year appeared on the market. Eight new extinguishers were brought out by four manufacturers, three of whom were new to the dry chemical field. One. an extinguisher of 6 1/4-lb. capacity has a dry chemical chamber of cast aluminum and an integral nozzle in the fill cap. Another type, in 20-lb. and 30-lb. capacities, is operated by inverting and bumping to puncture the cartridge, and is the only dry chemical extinguisher known to have been designed to operate in the inverted position up to that time. A third type, with outside cartridge, is operated by a trigger lever simultaneously releases carbon dioxide to pressurize the dry chemical chamber and opens a valve to release dry chemical into a hose leading to a horn-type nozzle.
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In 1950 only three new extinguishers were brought out and no new manufacturers entered the dry chemical field. These three units included a 4-lb. dry chemical extinguisher and a new type in the dry chemical field, stored pressure units in 2 1/2-lb. and 4-lb. capacities. The first mentioned 4-lb. unit is operated in the inverted position and is provided with a hose and shut-off nozzle. The stored pressure extinguishers are pressurized with nitrogen, not air, and have nozzles in the fill cap at the top of the units.
The foregoing discussion of hand extinguishers included only Underwriters’ Laboratories approved extinguishers.
In addition to the hand extinguishers, wheeled extinguishers are also available. Wheeled dry chemical extinguishers are pressurized by nitrogen from cylinders, the high pressure gas passing through regulating valves to reduce the pressure to about 200 lb. per sq. in. For some years wheeled dry chemical extinguishers in 150-lb. and 300-lb. capacities have been in use and in 1950 new 350-lb. and 150-lb. units were produced by manufacturers not previously in the dry chemical wheeled extinguisher field.
Other dry chemical fire equipment in use includes stationary units up to 2,000lb. capacity and fire trucks up to 4,000-lb. capacity. As mentioned before, automatically operated dry chemical piped systems are now in use in a number of locations. The large stationary units are used primarily for the protection of petroleum properties and the dry chemical is distributed through pipe lines to hose houses. In most cases, 1-in. hose and nozzles which will expell dry chemical at a rate of 450-lb. per min. are provided with these large stationary units.
With regard to large automotive dry chemical equipment, the United States Air Force has two 4,000 lb. experimental crash fire fighting trucks now being tested in Alaska. A 4,000-lb. capacity dry chemical crash fire fighting truck is being constructed for the Canadian Air Force and a 3,000-lb. dry chemical capacity fire truck, for Uruguay. Each turret nozzle on the 4,000-lb. capacity dry chemical crash fire fighting truck will discharge 1,500-lb. of dry chemical per minute and usually each truck of this capacity is equipped with two turret nozzles.
One of the well recognized characteristics of dry chemical fire extinguishing equipment is its ability to very rapidly decrease the intensity of the fire. There have been many attempts made to explain the extinguishing action of dry chemical and work is at present being carried on to definitely determine why dry chemical is such an effective extinguishing agent. Sodium bicarbonate when exposed to heat will break down to release carbon dioxide and water vapor and in doing so absorbs heat. The present theories of extinguishment by dry chemical assign the extinguishing action to the release of carbon dioxide and water vapor in the flame area, the absorption of heat by the solid particles, or the absorption of heat in the chemical reaction taking place when the sodium bicarbonate is decomposed. Regardless of which of these three actions is the most important, it is very probable that the extinguishing effectiveness of dry chemical is primarily due to the chemical action take place directly in the flames, whether it be cooling or smothering action that actually extinguishes the fire.
There is no question regarding the degree of effectiveness of dry chemical. The chart which compares the extinguishing effectiveness of various types of fire extinguishers on gasoline fires in steel-sided pans under standardized conditions, as determined by an approval agency, can now properly be shown before a group such as this because manufacturers of the other types of equipment are also manufacturing dry chemical fire extinguishers. It will be noticed that a 4-lb. dry chemical fire extinguisher is rated as being more effective on this type of fire than a 2 1/2-gal. foam extinguisher and that a 20-lb. dry chemical fire extinguisher is rated as being more effective than a 100-lb. wheeled carbon dioxide extinguisher. The 30-lb. dry chemical extinguisher is rated as being nearly as effective as a 38-gal. foam unit. Wherever flammable liquids and gases such as liquefied petroleum gas are handled, dry chemical fire extinguishers are very rapidly coming into increasing use.
Although dry chemical extinguishers are listed by the Underwriters’ Laboratories as being suitable only for flammable liquid and electrical fires, they have also been found to be extremely valuable in preventing the flash spread of fire in textile mills because the dry chemical settles over lint and prevents flame spread. This property of dry chemical has also been utilized to protect cotton storage, wherever there is paper dust in paper mills, and even in plants manufacturing excelsior. However, in all cases where dry chemical extinguishers are provided for preventing the rapid spread of fire in Class A materials, they should be backed up by water type extinguishers or standpipe hose to extinguish deep-seated fires.
It will probably he noticed that throughout this discussion the term “dry chemical” was used entirely instead of the term “dry powder.” The reason for this is that the approval laboratories, the National Fire Protection Association, and the National Board of Fire Underwriters all recognize the term “dry chemical” as applying to an extinguishing agent suitable for use on flammable liquid and electrical fires. On the other hand, the term “dry powder is similarly recognized as being applicable to materials for use on metal fires only. There are now extinguishers available for expelling dry powder on metal fires, and there is a greater chance of confusion now than in the past unless the term “dry chemical” is used for the types of extinguishers discussed today.