Nal Combustion Engine

NAL COMBUSTION ENGINE.) Such a vehicle is usually provided with a body for carrying hose and may be equipped also with ladders, pike poles, fire axes, crow bars, lanterns, hand fire extinguishers, nozzles, chemical fire engines and other accessories. In the larger cities fire-fighting equipment may also include ladder trucks which carry ordinary ladders as well as aerial ladders that are permanently attached to the vehicle and may be raised or lowered by a mechanism on the ladder truck. Water towers somewhat similar to the aerial ladders may also be used. High pressure fire engines have been developed to deliver water to the upper floors of high buildings in large cities.

History.

The earliest method of fighting fires consisted of throwing water on the fire from buckets or other vessels. It is not known what fire-fighting facilities were available at the time of the burning of Rome in A.D. 64. The first use of a device for applying water on to a fire in the form of a stream dates back as far as the 2nd century B.C. The science of fire extinction was still in a very elementary stage in the year 1666, when the great fire of London occurred. The only fire engines, used at this fire were those of the hand-operated type. The early squirting devices were usually in the form of a mammoth syringe. This later de veloped into a receptacle for holding water which was filled and replenished during the fire by a bucket brigade, the water being withdrawn and ejected by means of an early form of pump.

The pumps on the early fire engines were hand-operated and the range and force of the stream were poor. In many instances the engine was destroyed by the fire owing to the fact that the short range of the stream made it necessary to take the apparatus close to the flames. This led to the development of better pumps which could squirt a much longer distance. Subsequently, the development of a flexible pipe or hose made it possible to locate the engine well away from the fire and to convey the water under pressure from the engine to the fire. A still later development was the employment of suction hose to enable the pump to feed from other sources other than its own suction.

Steam Fire Engines.—The first mechanically operated fire engines appear to have been developed early in the 19th cen tury when steam was first used for operating a fire pump—the vehicle on which the pump and steam boiler were mounted be ing drawn to the fire either by the firemen or by horses. About 186o steam fire engines were being made in England and the United States. Public interest in steam fire engines was greatly stimulated by competitions held in England at the Crystal Pal ace in 1863, in which engines from the United States took part Steam fire engines were used almost exclusively at the Chicago, Ill., conflagration in 1871. Toward the end of the 19th century horse-drawn steam fire engines had been brought to a state of high perfection both in Europe and in the United States, when engineers began the development of the self-propelling vehicle. The earliest self-propelled machines were those of steam fire engines.

Motor Fire Engines.

The first self-propelled fire engines employing an internal combustion motor (other than as a tractor) were built about 1903. By 1910 a considerable number of motor fire engines were in successful service in various parts of the world and in 1928 practically every large city in the United States and many of the large cities in Europe had discarded horse-drawn and steam fire engines, in favour of self-propelled motor fire engines. However in some cases the old horse-drawn and steam fire engines are still sometimes used as reserve equip ment. a motor fire pump chassis is very strongly con structed in view of the fact that a fire engine is heavy and necessarily has to travel at high speed.

Various types of pumps are employed. The rotary gear type is a positive action pump which will draw its water from a depth of 20 to 25 ft. without being primed. The centrifugal pump is also employed but as this has no power of suction in itself it is either fitted with some form of priming device or with an auxiliary positive action pump for suction purposes. Piston pumps are also used and are very satisfactory under some conditions. In some cases a shaft is placed in line with the motor shaft which is used to drive the pump as well as the vehicle, through the use of separate transmissions.

Chemical Fire Engines.

These engines may be a part of a motor fire engine or may be mounted separately on a motor vehicle either alone or in combination with a body for carrying hose or other equipment. Chemical fire engines are of two types: soda-acid and foam. The soda-acid engine consists of one or more cylindrical vessels charged with a solution of bicarbonate of soda dissolved in water. Enclosed in this cylindrical vessel is also a receptacle for holding a quantity of sulphuric acid. A hose line generally a or 1 in. in diameter is connected to the outlet of the cylindrical vessel and when the chemical engine is required for use, the sulphuric acid is caused to be discharged from its receptacle into the bicarbonate of soda solution. This admixture of the acid with the soda solution within the cylindrical vessel forms carbonic acid gas under pressure, which forces the solution through the hose. In the soda-acid machines various methods for causing the acid to be discharged into the soda solution are em ployed : (1) inverting the acid bottle by means of an operating handle ; (2) revolving the cylindrical vessel on its trunnions, thus inverting the acid receptacle. The invention of these chemical fire engines has been especially helpful in fighting fires where there is a shortage of water, a problem which must often be faced in the out of town districts.

The foam chemical engines are a development from the soda acid chemical engine. The foam type of machine is somewhat similar to the soda-acid excepting that the acid ingredient is a solution of aluminium sulphate dissolved in water. The admix ture of aluminium sulphate solution with bicarbonate of soda solution produces a froth, but its bubbles are very easily broken down. To make the bubbles tougher and more stable a stabilizing ingredient is added to the bicarbonate of soda solution. The dis charge from a foam chemical engine is therefore a tough and tenacious foam made up of minute bubbles containing carbonic acid gas. This foam has the property of adhering to any burn ing solid surface upon which it is thrown and will even adhere to a vertical wall or to a ceiling ; it also floats on any inflammable liquid. This foam completely excludes air from the surface which it covers and deprives the fire of the oxygen which would other wise feed the flames, thus extinguishing the fire by suffocation. In the foam chemical engine as used on motor fire apparatus the two solutions are forced into two separate hoses which are joined together at their end into a common nozzle. The usual method of forcing the solutions from their vessels into the hose is by means of an inert gas contained in a pressure cylinder or by means of separate pumps. A more recent development of the foam chemical method of fire extinction consists in dispensing with the solutions and using the chemicals in their dry form. With this method a so-called foam generator is employed. A water supply under pressure is connected to one end of the generator and discharge hose at the other end. The dry chemicals are poured into the hopper of the generator as required at the time of fire. As the stream of water passes through the generator it automatically draws the dry chemicals into the water stream, re sulting in chemical action by means of which foam is discharged from the nozzle.

Fire Boats.

A very important feature of the fire-fighting equipment in large river, lake and sea ports is the fire boat. They are essentially large tug-boats equipped with fire pumps of 3,000 to 12,000 gal. capacity. The older boats were steam-propelled and the pumps steam-driven. The newer boats are propelled by internal combustion motors such as the very efficient Diesel engine which are not only employed to propel the boat but also utilized to drive the fire pumps when required. A boat recently built has a pumping capacity of 12,000 gal. of water per minute at about lb. pressure, is 1231 ft. long, 26 ft. beam and 71 ft. draught, and has been designed to travel at a speed of about 14 knots per hour.

Fire Extinguishers.

It is not uncommon for motor fire ap paratus to carry fire extinguishers of the soda-acid or foam type which are variants of the chemical fire engines described above and small enough so that they can be carried into a burning build ing by the fireman. Fire apparatus may also carry fire extin guishers of the carbon tetrachloride type which are particularly useful in connection with fires in electrical generating stations, etc., owing to the fact that the fluid is a non-conductor of electricity. (J. H. Os. ; C. B. R.)