country and have amply proven their worth. The introduction. of automobile fire apparatus, with its greater mobility and speed, increase in dependable pumping capacity and larger hose-carrying capacity, has in part made such systems no longer a necessity in other cities, where an ample water supply is available in the congested value district, or can be provided at a reasonable cost.

For cities having many acres of congested high value, and with an inherently inadequate water system for local protection, as in Chicago, such a system is of paramount importance and will be the only safeguard against the conflagration which present building conditions make probable. In like manner, no form of fire-fighting can take the place of that possible with a separate fire main system for protection where there is an excessive potential conflagration hazard as in congested resort places, or extensive water-front property or large groups of manufacturing or industrial buildings.

The question arises as to whether American cities, other than those which have such systems and the few which would come within the description above, will find it necessary, as they grow in size and value, to provide a separate fire main system. The remaining cities which are likely to reach metropolitan proportions can, by careful planning and the enactment of suitable laws, so restrict and protect their congested high value districts as to make such a system unnecessary. Where buildings are largely fireproof, especially the taller ones and those of large area, the hazard of spreading fires is largely reduced, particularly if exposed windows are protected. The contents of these buildings introduce fire hazards. equal to those in buildings of inferior construction and may exceed them because of congestion and greater volume, but fires in these contents should not introduce as great a conflagration hazard, as there will not be the danger of falling walls and floors and fire-fighting can be more effective. Also suitable laws should limit the danger of these fires by restricting their spread vertically in the building, and by requiring automatic sprinklers and other protective devices where the hazard is unusual.

Separate fire main systems constructed to withstand high pressures have been installed in New York (one in Manhattan, one in Brooklyn, and one at Coney Island), Philadelphia, Toronto (Ontario), Winnipeg (Manitoba), Cleveland, Toledo, Buffalo, Oakland, San Francisco, Baltimore, Boston, Detroit, Miami, Jacksonville, and Atlantic City.

In these cities the congestion of values and the probability of conflagrations are pronounced, and the value and need of such a system for the use of the fire department in combating fires is well recognized. In none of these cities, however, can it be assumed that such a system alone is adequate. Even though safe-guarded to an unusual degree, conditions in the larger of these cities, as to injury of mains during street construction and other causes, are such that all available fire-fighting facilities must be maintained. For that reason, the domestic water supply, with an ample number of hydrants, must be maintained as a reserve, and the fire department must be so equipped as to deliver water from it readily.

To sum up the advantages of a separate fire main system: a large number of powerful streams can be concentrated on a fire in much shorter time and with fewer men and less apparatus than with automobile pumping engines, and at the same time, the protection of the rest of the city would not be weakened to the extent now necessary on third and fourth alarms from the district covered by such a system; it will deliver its full capacity at any point in the district covered, and at any desired pressure, and can sustain this pressure as long as wanted; the system is not subject to depletion from losses due to possible broken domestic service connections leading into buildings involved; it eliminates the confusion entailed in the operation of a large number of pumpers; tends to prevent the misunderstanding of orders, and in every way simplifies operation. Above all, it provides protection to the congested value district, even with a general alarm fire under headway in another part of the city, and is the greatest insurance against conflagration, forming an effective defense against fires starting outside of the district and affording the most efficient means of checking fires in the district which might otherwise involve a number of buildings or even blocks.

Practical experience has shown that the following requirements should be made in the design of a separate fire main system to insure satisfactory fire protection in the district which it is to cover:

A fireproof pumping station with all openings protected in an approved manner, and removed from the zone of a sweeping conflagration; station to be equipped with sufficient pumping units of moderate capacity to aggregate a total capacity of 20,000 gallons per minute at 300 pounds pressure, taking suction from an adequate and reliable fresh-water supply, and delivering into the gridiron system through well-looped and gated discharge connections.

The distribution system to be connected with the pumping station through two or more supply mains, and to be so designed as to deliver the full capacity of 20,000 gallons per minute about any block within the area served without excessive loss of head; to contain no pipes less than 12 inches in diameter, no dead ends, and to be connected at all intersections; connections to be provided to the system so that fire boats, and suction to a second source of water supply, where available, may be used to supply the distribution system in case of emergency; the system to be provided with gate valves so placed that not more than 500 feet of pipe will have to be cut out at one time.

Hydrants to be of ample dimensions with 4 independently gated hose outlets, and connected to the mains through 8-inch gated connections; to be so distributed that the average area served by each shall not exceed 40,000 square feet.

It has been found desirable in most systems to provide independent methods of communication from the fire grounds to the pumping station, in addition to connections with public telephone, private fire department telephone, and fire alarm systems.

The type of pumping equipment and the kind of pipe installed in the distribution system of separate fire main systems already constructed are dependent partly on local conditions and partly on the conclusions reached by the designing engineer.

A separate fire main system, installed in 1902, protects most of the congested value district and an extensive manufacturing district in Philadelphia. The distribution system is divided into two zones, each supplied from a pumping station equipped with gas engines driving vertical, triplex, double-acting pumps. The pipe in the lower zone is tar-coated, flanged, cast-iron, and in the upper zone, tar-coated, cast-iron Universal. Total pumping capacity of both stations is 21,450 gallons a minute. The system is ordinarily maintained under a low head from the domestic distribution system and a reservoir. Pressures are raised upon receipt of fire alarms to 175 pounds, which can be increased to 300 pounds. The Borough of Manhattan, New York, has about ten square miles of its highest values protected by a system, the construction. of which was started in 1908. Twelve electrically-operated pumps. are housed in two fireproof pumping stations. Their total capacity is 43,000 gallons a minute at 300 pounds pressure. Pipe is tarcoated, bell and spigot, cast-iron. Pressures are raised from 30 pounds maintained from the domestic distribution system to 125 pounds in case of fire, and higher pressures are carried if needed.

During the first eight years that the system was in operation, pressures in excess of 200 pounds were carried ten times, and twice pressures in excess of 250 pounds were required.

A portion of the congested value district of Baltimore is protected by a separate fire main system, put in service in 1912. The fireproof pumping station contains three horizontal, twin, steam pumps having an aggregate capacity of 21,000 gallons. The pipe in the distribution system is lap-welded, open hearth steel. One hundred pounds pressure is normally carried by a small steam pump and is raised to 250 pounds in case of fire.

The congested value district and important mercantile and manufacturing areas of San Francisco are protected by a separate fire main system divided into two zones. The distribution system is cast-iron, tar-coated pipe, and is normally supplied by gravity from a storage reservoir and equalizing tanks. Normal pressures are from 130 to 140 pounds and can be raised to 250 to 300 pounds by turning in the upper reservoir.

The latest installation of this type, completed in 1921, protects the congested value district of the City of Boston. Pipe is tarcoated, cast-iron with specially designed, bell and spigot joints. Four pumps supply the system; two are installed in the generating station of the traction company and driven by steam turbine, and two are installed in a substation of the lighting company and driven by electric motors. They have a total capacity of 12,000 gallons. Normal pressures range from 40 to 60 pounds and are raised to 125 pounds and higher in case of fire.

In the preceding descriptions it will be noted that reference has been made to "separate fire main systems" rather than to "highpressure fire service systems." This nomenclature seems preferable because the service records of all such systems show that under normal operating conditions it is not necessary to carry excessive pressure above 200 pounds on such systems. It is the consensus of fire chiefs in each city where a separate fire main system has been installed that such systems are of inestimable value, and in many of these cities it can be stated without fear of contradiction that the systems have paid for themselves, sometimes by the service. they have rendered at one combination of simultaneous fires. Such was the case during the first year that the New York separate fire main system was in service.

CHAPTER XIV

RELATION BETWEEN FILTERED WATER STORAGE AND FILTER CAPACITY1

The gross output of filtered water obtainable in twenty-four hours from a water purification works, with all filters operated at a "normal" rate of filtration, is often termed the daily capacity of the works. Even after deducting the volume of filtered water needed for washing and other purposes at the works, however, the net quantity will not meet an equal average daily water consumption unless a sufficient volume of stored filtered water is available to provide for long-continued seasonal periods of excessive draft. Whenever hot, dry or freezing weather occurs, the use of water will rise, the extent of departure from the average depending upon the intensity and duration of the spell and upon local conditions such as metering, adequacy of plumbing, and prevalence of lawns and gardens. Winter and summer periods of high consumption occur in ordinary years in many parts of the temperate zone. The demands at such times can be satisfied only by an excess of filter capacity or by filtered water storage over and above that required to supply continuously the average daily draft for the year. The amount of reserve necessary is surprisingly large. Lack of sufficient provision in this respect frequently constitutes the cause for unexpectedly early enlargements of purification works.

Proper determination of the capacity of a proposed plant or of an enlarged existing one, capable of supplying a given annual average daily quantity of filtered water, is impossible except after consideration of the seasonal fluctuations of consumption that may be expected. Past records of daily water consumption, if of sufficiently long duration to include all local climatic variations likely to take place, may be accepted as a basis for computation. Where data

1 It should be noted that, in this discussion, the ultimate determination of total filtered water and service storage in relation to filter capacity is intricately bound up with matters of fire protection reserve, pumping equipment available, distribution system layout and relative costs. In this particular chapter only the elements of filter capacity and storage are considered. The reader must naturally consider and weigh the other elements in the problem when actual cases are under scrutiny.