PROCEEDINGS OF SECTION H. 645 



required at any point. " In small cities and outlying districts of large 

 cities 6in. cross mains, with 8in., lOin., or 12in. pipes at intervals of 

 four to six blocks, is a common arrangement. Four-inch pipe should 

 rarely be used to supply hydrants. For compactly built districts 

 many of the cross pipes require to be 8in., and a more frequent use 

 made of 12in. and 16in. pipes. A good arrangement for a compara- 

 tively large demand is to lay Gin. pipes lengthwise of the blocks and 

 Sin. pipes crosswise." This quotation is sufficient to indicate the 

 nature of American practice in the matter of street-reticulation and 

 provision for fire-extinction. Whilst Avith Australian prices its cost 

 would usually be prohibitive the general trend is undoubtedly on sound 

 lines. 



Mr. Thwaites states that to force one fire stream of 125galls. per 

 minute through a Sin. main a head of 29ft. per five chains length would 

 be required, whilst for two he puts the corresponding head at 116ft. 

 These heads are somewhat in excess of those generally allowed for 

 clean pipes, and evidently include an allowance to cover any resistance 

 due to corrosion. And yet in Victorian urban water supplies 2in. 

 and l^in. galvanized iron mains have been freely used, and in some 

 cases even smaller sizes have been adopted, and this notwithstanding 

 that in many cases the supplies come from wrought-iron or steel tanks 

 placed at comparatively low elevations. In many cases articles des- 

 troyed by fire cannot possibly be replaced at any cost, and insurance 

 cannot compensate for losses sustained through the disarrangement 

 of business. Hence effective fire-protection pays in more ways than 

 in the reduction of insurance premiums ; but such protection is not 

 secured unless the reticulation pipes are of diameters sufficient to allow 

 of effective fire streams being supplied. 



Whilst it is most desirable that the reticulation should be capable 

 of delivering good fire streams at satisfactory pressures direct, in many 

 cases the local conditions will not permit of this ; and in such case 

 the most satisfactory arrangement is to discharge from the hydrants 

 through short lengths of hose into canvas tanks, from which the water 

 is delivered on the fire by steam or hand fire engines. By this means 

 the reticulation is relieved of the back pressure from hose and nozzle 

 resistance, and hence can deliver the water at a more rapid rate. 



The usual diameter of fire hose adopted is 2|in., and to discharge 

 a fire stream of 125galls. per minute through such a hose the velocity 

 must be 576ft. per minute, or 9Jft. per second. In a pipe line the 

 resistance under such conditions would be so enormous that no engi- 

 neer would attempt to convey such a stream at such a rate. According 

 to Freeman's classical experiments the resistance with the best rubber 

 hose under such conditions would be about 71bs. per 100ft., and with 

 ordinary canvas hose over 161bs. per 100ft. Hence it is desirable 

 that the lengths of hose required should be reduced as much as possible 

 by having fireplugs spaced fairly close together, and that the hose 

 diameter should be increased so as to reduce the frictional resistance 

 per unit length. A fireplug spacing of five chains or a little farther 

 is usual, and Mr. Thwaites suggests intervals of 100yds. in closely 



