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10
At the top of the works is a very large container technically
known as a "spreader," which as part of its function contains a
highly explosive gas. In order to render this as harmless as possible,
this gas is mixed with a certain proportion of CO2. The
accuracy of the mixture, on which its safety depends, is ascertained
by the fact that the gas in question is compressible whilst
the CO2 is not at a certain pressure. The compression for this
purpose is obtained by a head of water acting in the " concentration
head."
The concentration gauge was originally set to be used for canal
water from the works' tank. At that time the drinking water in
the works was obtained from their own artesian well.
The canal water proved that it was not of sufficient purity to
use in the concentration gauge, and for that reason the well water
was coupled in. Some time after this trouble arose with the well
supply owing to machinery breakdown, and the drinking water
supply was changed over to the Metropolitan Water Board's supply.
All the drinking water pipes are on the "well" system, so that
these pipes were used for Metropolitan Board's water. The
Metropolitan Board's water was supplied by a temporary pipe, and
volume and pressure were very fluctuating, with the result that they
were not getting a permanent supply anywhere in the factory. For
this reason the supply to the concentration, gauge was recoupled to
the canal water supply.
The pressure in the canal water supply was greater than the
Metropolitan Water Board's supply, and the result was that the
valve between the two having been opened by someone, the canal
water forced back the Metropolitan Water Board's supply at the
lower pressure, and so gained access to the drinking water system
throughout the works.
This supply was immediately severed, and the service pipes
emptied and flushed out with Metropolitan Water Board water before
restoring the drinking water service.