Requirements of Water Works Systems for Fire Protection
The experience of many departments, as well as of public service corporations engaged in similar work, is that the motor-driven vehicle has become a necessary adjunct to the equipment of every water works system. It enables a prompt response in case of accident, and increases the efficiency not only of the executive force, but also of the laborers in many branches of the work, There is hardly a plant of any magnitude on which one or more automobiles cannot be profitably operated. The source of supply must be carefully studied before its adequacy from the fire protection standpoint can he determined with certainty. The total quantity of water used for the extinguishment of tires is proportionately very small, being approximately one-tenth of a gallon per capita per day, or in round numbers about one-thousandth ot the total consumption, but for short periods of time the rate is very high, f rom a perusal of the consumption records of any well operated works, the maximum hourly, daily and monthly rates can be readily determined, and from a study of the structural conditions m the city—areas, heights, protected openings, exposures, occupancies, construction of buildings, etc. the probable maximum quantity which would be required to combat a lire of largeproportions can he. estimated within reasonable limits. The number of fire streams required simultaneously in cities of average character has been discussed by our leading hydraulic engineers, with practical unanimity of opinion, Their estimates are based on actual practice, and the values given by Mr. Kuichling are expressed by the formula Y = 2.8 √x, where Y equals the number of 250 gallon streams and .v equals the population in thousands. This formula does not make any allowance for broken services, and should be applied only after a study of the local conditions has been made, for in many cities the size of the mercantile or manufacturing districts is not in proportion to the population, A very full discussion of this subject was presented to the American water works association last year by Messrs. Metcalf, Kuichling and Hawley. Although the chance of a large fire occurring during the hours of maximum consumption is somewhat improbable, nevertheless it is wise to err on the safe side, and to use the maximum hourly consumption figure in the calculations, although in most cases the maximum daily rate may be used with comparative safety. This step is not so unreasonable as at first appears, for any city should have its supply developed somewhat in advance of present requirements, in order to care for future growtu. In cities not exceeding 100,000 in population, where the lawn sprinkling is restricted to certain periods of the day, it is feasible to enforce an ordinance prohibiting irrigation during the progress of a fire, thus materially reducing the maximum rate for which the city would otherwise have to provide. In some cities, dependent upon fire engines, the pressure is so reduced by large fire drafts that the domestic consumption rate will drop appreciably. Such distribution systems cannot, however, he considered adequate for the service required of them. There are many cities located on large lakes and rivers where a practically unlimited supply is available, and one does not have to give the question a thought, lutt in others, it is a most important question with the engineer. In these latter the problem is varied hut re -dvrs self into some method of storgae so that the maximum rates can he delivered to the distribution system. If the supply is derived from driven wells, they should be so developed as to furnish the maximum daily rate, and the maximum hourly and lire-flow rates may economically he cared for by a storage in a covered reservoir available for delivering into the distribution system. If the supply is derived from storage from a large catchment area, the capacity of this storage should be ample to meet the demands made upon it through a series of dry years. In dealing with such a supply, the average daily con sumption, and not the varying hourly rates’ must he considered in determining the minimum capacity of the storage reservoirs.
The source of supply having been determined, the method of delivery to the distribution system confronts us. In many cases where the supply is derived from rivers and lakes, and generally when delivered from storage reservoirs, these sources are at an elevation sufficient to deliver the supply by gravity In a few cases the topography of the country is such that the sources of supply are in close proximity to the distribution system, but in by far the greater number they are at some distance. In the latter cases, distributisg reservoirs within or near the area served by the distribution system become an economical necessity, for their existence permits the use of much smaller conduit lines. These lines should have a capacity at least equal to the maximum daily consumption, and one such line cannot be depended upon unless the storage in the distributing reservoir is ample to furnish the supply during the longest period that will lie required to make repairs. The conduits delivering the Catskill supply to the city’of New York, the Owens river supply to Los .Angeles, and the Wacusett supply to the metropolitan district of Boston, are not in duplicate, but The permanency of their construction and the storage provided along their routes and at their termini asures the continuity of the supply. On system’s where there is more than one supply line, these lines should not follow the same route, as the failures of one may cause the failure of another, or both may be put out of service at the same time from the same cause, as was recently the base in Seattle, Wash. Where pumps are required to deliver the supply to the distribution system, the pumping station should he of fireproof construction. No valid excuse can he offered for not constructing stations absolutely fireproof. The installation of sprinkler equipment, standpipes equipped with hose, and chemical extinguishers in the many existing stations which are not fireproof, should be strongly advocated. In all cases, oil should be stored outside the building, and all internal hazards should be reduced to a minimum. When stations are exposed to external hazards, outside sprinklers, water curtains and wore-glass windows should be provided. On buildings having incombustible roof coverings and cornices these give reasonable protection.
The selection of the equipment of the station requires careful study in order that units of proper capacity and number to insure economic and continuous service may be provided. Plants which are supplied by pumpage may be broadly divided into three classes, namely, those which distribute from a storage reservoir, from an equalizing reservoir, and direct from a station. Under the latter class those which are supplied with an equalizing standpipe should be included, for in only small towns can a standpipe furnish any reasonable proportion of the draft, and in the larger cities it is a useless adjunct, as the pressure can be as uniformly maintained by means of pressure governors. The stations which deliver direct to the system will first be considered. Their pumping capacity should be sufficient to deliver the maximum domestic and fire draft combined, with any two units in reserve; and the boiler capacity should be sufficient to enable the pumping of this maximum draft by the most uneconomical units in the station, with one boiler out of service for repairs or cleaning. This requirement of two reserve pumps over and above the maximum capacity has frequently been questioned, one of the foremost objections offered being the large amount invested for machinery which may never be called info use. The answer to this objection will be given along the line of cost. If the city were located in close proximity to a hill of sufficient elevation to furnish the desired pressure, the advisability of building a reservoir of sufficient capacity to assure the supply would not be questioned. Such a reservoir would cost, in round numbers, about $5,000 per million gallons, which corresponds closely with the cost of high duty pumping machinery of equal capacity; and low duty or centrifugal pumps can be purchased at a much lower figure. Viewed from the cost standpoint, therefore, no argument can be adduced against installing pumps to perform the same function as the reservoir. Where an equalizing reservoir is in service, the pumping capacity need not he as great as in the preceding case, but there should be one unit in reserve over and above the maximum possible draft for ten hours, minus the reservoir capacity. When a station delivers to a storage reservoir, the pumping capacity should be equal to the average daily draft during the maximum month. Such capacities may perhaps appear high to many who have successfully maintained an ample supply from stations which are not equipped with the abovementioned reserve units, but no station can be considered reliable unless it can maintain the supply at all times, and it is not infrequent in a station containing four or five units for two to be out of service at the same time, and, although one of the units may be undergoing only trival repairs, such as replacing valves or packing glands, it would, nevertheless, be impossible to get it back in service on short notice. The capacity for coal storage should be sufficient to hold fuel enough to run the plant through any period in which the delivery may be interrupted by strikes or unfavorable weather conditions, and coal to meet such emergencies should, of course, he kept always on hand. If the water is delivered direct from the pumping station to the distribution system or to an equalizing reservoir, there should be two or more discharge mains, and their capacity should be such that with any one main out of service, the other or others could deliver somewhat in excess of the maximum domestic consumption; and, of course, it would be much more desirable if. under such circumstances. the maximum domestic and fire draft combined could be provided for. When delivering into a storage reservoir, one main having a capacity equal to the maximum daily rate is ample. for repairs can be made before the water in the storage reservoir will be exhausted.
To-day filtration plants are in operation in many cities, and the capacity of these plants need not be as great as the maximum hourlyrate of consumption if enough filtered water is held in storage at some point on the works to provide for the drafts. On many plants this supply is provided by large covered clear water basins which supply the high lift pumps. In some plants a by-pass is installed, so that unfiltered water can be delivered direct into the distribution system in case the fire draft exceeds the capacity of the filters and exhausts the supply in the clear water basins. W here the original source is contaminated, however, this expedient should not be resorted to, but provision should rather lxmade lor additional clear water storage, as an epidemic is even more undesirable than a conflagration. The supply mains connecting the storage or equalizing reservoir with the distribution system should be by-passed around the reservoir, and of such capacity that the maximum rate can be delivered with any one main out ot service. In some cases, the installation of cross connections and suitably located gates in the supply mains enables their size to be somewhat reduced. Blow-offs should be established at all low points, for it often requires more time to empty a main and dispose of the water than it does to accomplish the actual repair work. In the construction of force and supply mains, the question of material is often difficult to settle. Last iron, wrought iron, steel and wood are each Used with good results. Up to 30 inches in diameter, cast iron generally proves the more economical, but in larger sizes steel lines prove cheaper even if they have to be replaced within 25 or 30 years. Besides, it is impracticable to use ca-1 non in mains ot more tnan 00 inches in diameter. The carrying capacity of lines constructed of either material gradually decreases, but the cast iron lines can be cleaned and their capacity restored at a nominal cost. On the other hand, cast iron is subject to rupture, which will put the line completely out of service, while in the case of steel any general weakening of the structure is portended by small leaks. Continuous wood stave pipe has proved very reliable; it is almost always cheaper, can be readilyrepaired, and maintains its carrying capacity throughout its life.
*paper read at Convention of New England Water works held in Washington, D. C., 18. 1912. by Clarence Goldsmith, Assistant Engineer Public Works Department, Boston.
All force and supply mains should be equipped with air valves at their high points, and they should be frequently inspected, for a defective air valve will cause a steel or wood line to collapse in case of a break at one of the low points. There is no better item to observe than the per capita consumption records if one cares to make a snap judgment in regard to the efficiency of the operation of a water works system, for almost invariably the high consumption rate is a sign of inefficiency, and, conversely, the low consumption rate is indicative of efficiency. The per capita rate which is necessary to meet modern conditions in our Cities ranges from about 50 to 150 gallons per day, but these rates are exceeded in most of them. This unnecessary consumption has a very important bearing upon the question of cost, for it has to be met by the development of larger supplies, the construction of additional filtration works (if there be any), and the installation of additional pumpingequipment and of force, supply and distributing mains of increased carrying capacity, if the domestic and fire-flow requirements are to be fullymet. Unfortunately, in such instances the fireflow is generally only partially provided for during periods of maximum domestic consumption. The installation of meters is the surest and practically the only way to effect a permanent reduction of the per capita rate. Many and fallacious as are the arguments advanced by the opponents of the general installation of meters, the results where they have been installed are incontrovertible. Water works engineers are not as yet agreed that the metering of all services is an economic necessity, but the results attained in cities that have metered practically every service, show that as much benefit may be derived from metering the last 10 per cent, of services as was obtained from any prior installation of an equal number of the same size. The water used in public buildings and for other municipal purposes is generally far in excess of that actuallyneeded. In cities which have paid particular attention to this class of consumption, the conclusion reached is that all water used by the several city departments, except for the extinguishment of fires, should be metered and paid for by the users. Such a course not only effects an important reduction in consumption, but gives the water department credit for the service rendered.
One of the points upon which insurance and water engineers differ is in regard to the metering of fire services. The w-ater works engineer, who generally takes the affirmative side of the question, is in much closer touch with the situation, and when such results as the following are obtained, there seems to be no doubt in regard to the justification of his stand. Worcester, Mass., metered all fire services in 1905. and the following year the revenue increased $15,000, and the consumption decreased over 300,000,000 gallons. Lockwood, N. Y., metered all fire services, and the following year the revenue increased 25 per cent, and the pumpage decreased 20 per cent. The pressures which are maintained on works which are supplied by gravity from distributing or equalizing reservoirs are governed by the elevation of the reservoirs. in many cases suitable sites are not available at desired elevations, but when they are, it is highly desirable to so locate the reservoir that a pressure of 100 pounds will be maintained over the greater portion of the distribution system, and particularly in the closely built-up sections. In a recent paper,* E. V. French dwelt upon the advisability of such a pressure, and showed that it was sufficient to furnish direct hydrant hose streams to all tires except those in the larger and higher buildings, for which more powerful streams would have to be furnished by fire engines. As the number of fire engines can he greatly reduced if any streams can be taken direct from the hydrants, a very considerable saving can be thus effected, for it costs between $3,000 and $4,000 a year more to maintain an engine company (horse-drawn) than to maintain a hose company, in planning for extensive improvements in any city, therefore, it is desirable to provide, if possible, for the raising of the pressure to about 100 pounds, for in addition to cutting down the expense of the fire department, other economies can in this way be also effected. Take, for example, the large cities of new York, Chicago, Philadelphia and Buffalo. In these it is necessary to pump all the water used in buildings of moderate height and in small plants, and this could be done more economically in one central station. Of course it would still be necessary to pump the supply to buildings over 200 feet in height, but these are comparatively few.
Next in importance to the saving which could be accomplished is the increased reliability of sprinkler equipments when supplied from a central station. The number of such equipments in service is increasing rapidly, and they constitute practically the only safeguard to buildings of non-fireproof construction and fireproof buildings containing combustible material. In many systems supplied by direct pumpage, provision is made to raise the pressure upon receipt of fire alarms and maintain this pressure until the “all out” is sounded. This practise is good, and may well be adopted in all such systems. The permanent raising of pressure on a system does not necessarily increase the consumption, for thorough inspection and the prompt following up of defects will enable an unincreased consumption rate to be maintained. This has been proven in several cities during the past few years, and though heavier materials, requiring more careful workmanship, are used in the original installation, the subsequent cost of maintenance of a distribution system under 100 pounds pressure is no greater than under 50 pounds pressure. Few engineers have the opportunity to design a new distribution system for a city of any considerable size. New Orleans is the only large city which has installed a new piping system in the last score of years. The problem of to-day is the reinforcement and rehabilitation of outgrown distribution systems, or of systems which have deteriorated in carrying capacity or were faulty in their original design. To accomplish this task, a careful study of the existing system should he made, present requirements determined, and proper allowance made for future growth. This done, a plan for all future work should be adopted and followed. This plan should include main arteries of ample carrying capacity girdling the city as its growth demands, secondary feeders of suitable size about 3,000 feet apart in either direction, and dead end lines extended to outlying sections without reduction in size the system to he so designed as to furnish fire protection as follows:
- In outlying residential districts not likely to become closely built up, a minimum of 1,500 gallons per minute.
- In closely built up residential and minor mercantile sections, 2,000 to 5,000 gallons per minute.
- In manufacturing, warehouse, and congested value districts, from 5,000 to 20.000 gallons per minute, depending on the structural conditions.
The above supply should he in excess of the maximum daily domestic consumption, and should be available in manufacturing districts to any large group of buildings of special hazard, and in mercantile and residential districts about any block in or rder that these quantities shall be available. the following minimum sizes of mains should be used for hydrant supply: For residential districts, 6-inch and 8-inch mains, the former to l>c used only where they complete a good gridiron, and the latter in locations where dead-ends and a poor gridiron are likely to exist lor some time, and in all blocks 600 feet or more in length. For mercantile and manufacturing districts. 8-inch and 12-inch mains, the former to be used only in sections where they complete a good gridiron, and the latter for long lines not cross-connected. Four-inch mains cannot furnish sufficient hydrant supply, and should be replaced as fast as circumstances will permit, the replacement to commence in the more thickly built up sections. In order that not more than one hydrant will be on a 6-inch, nor more than two hydrants on an 3-inch main between intersecting lines, dead-ends should he eliminated wherever practical, large mains cross-connected to distributors at all intersections, and long unsupported lines of pipe cross-connected. The city of Reading. Pa., affords a good example of the results which may he accomplished by the adoption of a well designed plan to be followed out in future construction. Some 17 years ago such a plan, prepared by the superintendent. E. L. Muebling, was approved by the city, and has been followed since that time. At present there are ample quantities of water available for both domestic and fire protection purposes throughout the entire system, and future additions to meet increased growth in population can he readily and economically made. Unfortunately, the topography of some cities precludes the making of plans for future growth, for it is impossible to foresee in what direction that growth will extend. For a number of years the probable growth of Los Angeles appeared to he in an easterly direction, and it is only in the past two or three years that a definite trend showed it to be in a westerly and southerly direction.
Tar-coated cast iron pipe is unquestionably the best material to install in a distribution system. In some parts of the country kalamcined pipe is extensively used, because of the saving in freight rates which can be effected on account of its lighter weight, and this pipe gives very good results. Machine banded wooden pipe does not give satisfaction in a distribution system on account of the excessive leakage wdiich generally occurs. Cast iron pipe should be inspected at the foundry and again before it is lowered into the ditch. Special care should be taken to prevent any foreign matter from getting into the line during laying, and the line should be thoroughly blown out before it is put into service. If practicable, a test pressure of one and a half times the working pressure should be applied to the line before backfilling. Pipe less than 6 inches in diameter should never be installed to furnish hydrant supply. In cities where the distribution system is weak, it is desirable not to install any pipe less than 8 inches in diameter, for the new lines of these larger sizes will reinforce the old lines. The weight of pipe purchased should lie sufficient to enable at leasl 300 feet head to he maintained at the point of lowest elevation in the city. If the heavier classes of pipe are installed, it enables the pressure on the system to he raised to the desired point without the additional expense which would otherwise be required for relaying. The coefficient of carrying capacity ot the older lines should he determined by experiment, and in many cases, where the supply is deficient, the results obtained will show that it is more desirable to clean the line than to lay a new line. Sufficient cover should be provided to insure the pipe from freezing, even in the coldest winter. Exposed pipes at bridge crossings should be well supported and protected from injury, and extreme care should be paid to the design of the line near the approaches. Electrolysis is a subject which must not be neglected, for it is most insidious in its action. Frequent surveys should he made, and remedial measures approved by the best water works practise, rather than those generally advocated by street railroad engineers, should be adopted. Grounds from electric circuits should he made on the street side of the meters, main Cocks, etc., in accordance with the National Electrical Code, and no power circuit which depends upon a grounded return should he connected to the system in any manner.
(To be continued.)