QUESTIONS & ANSWERS

QUESTIONS & ANSWERS

DEPARTMENTS

Pumper Acceptance Tests

To the Editor:

I have read about the three-hour acceptance test for new pumpers. Are there any additional tests recommended?

R. T. M.

Answer: The National Board of Fire Underwriters recommends that, in addition to the regular three-hour acceptance tests, the apparatus be given:

A short overload test to show its ability to develop 10 per cent excess power. The test should consist of discharging rated capacity at 165-psi net pump pressure.

A test conducted when operating at draft to determine the efficiency of the means provided for automatically controlling pump pressure. With the pressure control set at 10 psi higher than any operating pressure over 75 psi and the pump discharging through one or more hose lines, pump pressure should not increase more than 30 psi when hose outlet valves are closed slowly.

A vacuum test, with a capped suction at least 20 feet long, should develop 22 inches of vacuum and hold the vacuum with a drop not in excess of 10 inches in 10 minutes.

Endothermic-Exothermic Reactions

To the Editor:

Will you explain just what endothermic and exothermic reactions are? Answer: Endothermic and exothermic reactions are chemical reactions between different substances. In the endothermic reactions the new substance formed contains more energy than the original reacting materials, while in the exothermic reactions the new material contains less energy than the original reacting materials.

Exothermic materials are generally more stable since they have given off energy (usually in the form of heat) in the reaction. Endothermic materials, such as carbon disulfide, having absorbed more energy than the combining materials originally possessed are highly unstable and will vigorously polymerize, decompose, condense, or will become self-reactive when exposed to air, water, heat, shock or pressure.

Common commercial explosives are generally manufactured from endothermic compounds.

Questions & answers

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Questions & answers

Handling Chimney Fires

To The Editor:

What method would you recommend for extinguishing chimney fires? In our town these fires result from the use of wood-burning furnaces and the chimneys are of brick construction without tile interiors but do have clean-outs. It is our current practice to direct a stream of water up the chimney from the clcan-out in the basement. However, others recommend using soda-acid extinguishers. What other methods exist and which is preferable?

B.O.D.

Answer: Generally water is best applied from the top of the chimney downward in the form of a light spray. Since water is the extinguishing agent in both cases it makes little difference whether a fog nozzle or a soda and acid extinguisher is used except that some baffle such as a stick should be used to break up the extinguisher’s stream in the form of a spray. A stream of water shot into the clean-out in the basement would have to make somewhat of an angled turn and might not reach far enough up into the chimney. Increasing the pressure on this stream to reach the top would probably force water through cracks or faults in the chimney and stain interior walls.

Many departments use the light water spray, from the top in conjunction with a rope-and-chain, quite successfully. In this operation a bound cluster of chains is lowered into the chimney on a rope at least as long as the chimney. Manipulating the chain in the chimney enables it to knock or scrape off burning soot from the walls which falls into the clean-out. The water completes the job.

Some departments use chimney fuses which are in effect smoke and gas bombs (resembling railroad flares in appearance) which fill up the chimney with a heavy gas-smoke atmosphere and dilute the oxygen content to a point where combustion ceases.

Engine and Brake Fires

To The Editor:

I have heard you shouldn’t use water on an automobile motor fire. Yet I have seen foam recommended in print. I have heard it argued that carbon dioxide is so cold that it can crack an engine block. What is your opinion on this? Also, what about using water on overheated brake shoes?

J. J. T.

Answer: Fires in automobile motors fall into two categories: Those in wiring caused by short circuits and those caused by flooding or breakage of fuel lines involving burning gasoline. Water, carbon dioxide, foam, and dry chemical can be used to extinguish both types of fires, depending on the severity.

Generally, water in the form of spray may be used on vehicle electrical wiring. It not only knocks down flame, but also provides sufficient cooling and quenching effect to penetrate the burning wire. There are no cases known to FIRE ENGINEERING in which the small quantities of water used at most automobile fires has cracked or otherwise damaged the block or other metal parts of a motor. Water fog is also an effective medium for gasoline fires around motors where the quantity is naturally limited.

Carbon dioxide is highly effective on confined gasoline fires and will have a limited effect on burning wiring. However it is a gas, and can be carried away by wind and the convection currents surrounding the fires, thus presenting the possibility of reignition from hot metal parts. The expansion of liquid carbon dioxide as it is ejected from the extinguisher chills it to a low temperature at which point a portion is turned into the solid form appearing as snow or dry ice. This snow rapidly turns back into gas (sublimates) and there is seldom the time, nor a sufficient quantity of it to harm hot metal parts.

Foam is highly effective on gasoline fires and reasonably effective on fires in wiring. It leaves a residue which must be cleaned off the motor and its use may not be warranted in a small fire. Its water content which provides a cooling effect should have no effect on hot metal parts since it contains about 10 parts of air and foam-forming material to one part of water.

Dry chemical extinguishers are generally most effective and recommended for both the Class B and C fires found around automobile motors.

Automobile brakes consist of a brake shoe and a drum, both incombustible. Any fire found around brakes will be in either grease accumulations or in the hydraulic fluid. These may be extinguished with water spray. Most cases of overheated brakes do not involve fire and they should be left to cool naturally. Using large quantities of water can possibly warp the drum incurring unnecesssary damage and expense.

British “Siamese” Terminology Differs

To the Editor:

I was interested in your “Siamese Terminology” on page 149 of the February 1963 issue of FIRE ENGINEERING, but I understand British terminology differs from ours. Can you help me on this?

A. G.

Answer: British terminology does differ from ours. For a “wye” British firemen use what is termed a “dividing breeching” since the function of the piece is to divide one line into two lines. For “siamese” they use “collecting breeching” since the function of the piece is to collect two lines into one line.