(c) Must be arranged so that the carbide holders or charges may be easily and entirely removed in case of necessity.
18. GASHOLDERS.--(a) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.
Gas-bells, if used, may be two gauges lighter than holders.
Condensation chambers, if placed under holders, to be of same gauge as holders.
(b) Must be of sufficient capacity to contain all gas generated after all lights have been extinguished.
If the holder is too small and blows off frequently after the lights are extinguished there is a waste of gas. This may suggest improper working of the apparatus and encourage tampering.
(c) Must, when constructed on the gasometer principle, be so arranged that when the gas-bell is filled to its maximum with gas at normal pressure its lip or lower edge will extend at least 9 inches below the inner water-level.
(d) Must, when constructed on the gasometer principle, have the dimensions of the tank portion so related to those of the bell that a pressure of at least 11 inches will be necessary before gas can be forced from the holder.
(e) The bell portion of a gasholder constructed on the gasometer principle must be provided with a substantial guide to its upward movement, preferably in the centre of the holder, carrying a stop acting to chock the bell 1 inch above the normal blow-off point.
This tends to insure the proper action of the bell and decreases the liability of escaping gas.