MIL-HDBK-1027/1B
amount of propane that can be placed in a tank over 4550 L water
capacity as shown in Table 4-5.2.1 of NFPA 58 is 45 percent of
the water weight capacity of the container. Then Table
4-5.2.3(b) shows that at 15.9 degrees C temperature the
container can be filled to 88 percent. It is, thus, important
to have accurate gauging devices. Such tanks generally have a
variable gauge for general inventory control. The gauging
devices are generally a float magnetic gauge with an indicator
dial to show the percentage full of the contents at different
temperatures; however, the gauging devices are not accurate
enough to use them for maximum fill control because the float
arm may become bent or other malfunction may occur that throws
off the accuracy. As a result, a fixed liquid level gauge is
required. This is a tube into the tank with the tube length
made to extend down to the proper liquid level of 88 percent.
There is a small valve with a restricted opening at the outer
end. On filling of the container, the operator opens this valve
and vapor will flow out during loading until the liquid reaches
the bottom of the tube where a white cloud will appear at the
outlet valve. This is not liquid propane but rather it is a
water vapor cloud which is created when liquid propane expands
to vapor and resulting refrigeration condenses the moisture in
the air and creates the white cloud as fog. When this occurs,
the operator should immediately shut off the flow of propane
into the container and then shut off the gauge valve.
Generally, at firefighting schools, transport trucks will be
used.
k) Propane will be delivered to the containers by
transport truck or, in some cases, by tank car. Generally at
firefighting schools, truck transport will be used. Truck
transports are generally 30 000 to 42 000 L capacity. Usually,
such transports are equipped with an unloading pump. In such
cases, the unloading hose is connected to the storage unloading
station liquid line for unloading. The vapor return hose is
also connected to the storage tank vapor line. This connection
assists in the liquid transfer as it prevents a buildup of vapor
pressure in the receiving tank. The transport might be equipped
with a vapor compressor instead of a pump to use for
off-loading. Off-loading involves vapor being drawn off the
storage tank and discharged into the transport tank which
creates a higher pressure differential in the transport tank and
thus forces the liquid to flow into the storage tank. When the
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