MIL-HDBK-1027/1B
Remote shutoff control should be located at the
24-hour duty station and at each fence opening. The truck
unloading station emergency shutoff should have a dual control
of cable release and remote shutoff.
q) Normally vapors for use will be drawn off of the
container from the vapor space above the liquid. Propane boils
from a liquid to a vapor at a liquid temperature of minus 42.2
degrees C or above and thus replaces the vapor being used.
However, this evaporation creates heavy refrigeration which
cools down the temperature of the liquid. If the draw is heavy
enough it will result in insufficient vaporization thus
requiring the use of a vaporizer to convert the liquid to vapor.
r) There are two basic types of vaporizers. One is
the indirect type which is heated by a heating unit remote from
the vaporizer. The indirect type should furnish heat by steam,
hot water, or other heating medium. The other is a direct-fired
type. The standards for vaporizers is detailed in NFPA 58.
Many times a pump is necessary to provide the necessary flow
from the storage tank to the vaporizer because if the vapor
pressure in the storage tank gets low, the proper quantity of
liquid will not flow to the vaporizer, thus the need for the
liquid pump. The installation should be in accordance with NFPA
58 and should have the electrical equipment in accordance with
NFPA 70, National Electrical Code. Waterbath and indirect-fired
vaporizers are both acceptable for use at firefighting training
facilities. Use an indirect-fired vaporizer when there is a
sufficient sized central steam or high temperature hot water
heating plant or system available. In this case, the
indirect-fired vaporizer would be less expensive than the
waterbath vaporizer. Use a waterbath vaporizer when there is no
central heating plant or system available. In this case, the
waterbath vaporizer would be less expensive than an
indirect-fired vaporizer and a new heating plant. No
direct-fired vaporizers other than the waterbath type are to be
used.
s) When using indirect-fired vaporizers, NFPA 58
applies. FM Loss Prevention Data, Section 7-55/12-28, Liquefied
Petroleum Gas apply. In addition, install and design the
waterbath vaporizer in accordance with the following:
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