This precaution is
necessary because, while the acetylene is displacing the air in the
pipes, they will for some time contain a mixture of air and acetylene in
proportions which fall within the explosive limits of such a mixture. If
the escaping acetylene caught fire from any adjacent light under these
conditions, a most disastrous explosion would ensue and extend through
all the ramifications of the system of pipes. Therefore the first step
when a new system of pipes has to be cleared of air is to see that there
are no lights in or about the house--either fires, lamps, cigars or
pipes, candles or other flames. Obviously this work must be done in the
daytime and finished before nightfall. Burners are removed from two or
more brackets at the farthest points in the system from the gasholder,
and flexible connexions are temporarily attached to them, and led through
a window or door into the open air well clear of the house. One of the
brackets selected should as a rule be the lowest point supplied in the
house. The gasholder having been previously filled with acetylene, the
tap or taps on the pipe leading to the house are turned on, and the
acetylene is passed under slight pressure into the system of pipes, and
escapes through the aforesaid brackets, of which the taps have been
turned on, into the open.
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