SCENARIO #5
MC-331 CARGO TANK TRUCK WITH PROPANE LIQUID LEAK
A driver of an automobile lost control of his vehicle at high speed, and drove under the right side
of an oncoming MC-331 cargo tank truck, which was making a righthand turn onto a bridge.
Upon arrival at the scene, the Incident Commander (IC) sizes up the situation. Under the
protection of hoselines and in full protective clothing and SCBA, firefighters approach the
accident site and find the automobile wedged under the propane truck, with the car's roof crushed
level with the dashboard. A quick survey of the driver's injuries confirms that he has received fatal
injuries. The propane truck driver has received minor injuries which will require medical treatment
at the hospital.
Inspection of the damaged tank truck reveals the truck is placarded "1075" (the correct placard
for propane). The truck is painted with the name of the propane transport company.
Under the protection of hoselines, a fire department officer observes that the truck's piping is
severely damaged and has cracked open. The valve stem appears to be bent and is producing a
gas cloud. A liquid propane leak is observed on the bottom, lower section of the tank.
SUMMARY OF TANK TRUCK CONSTRUCTION FEATURES
MC-331 cargo tanks have a maximum design pressure of 500 psig [49 CFR 178.337-1(b).] They
are constructed from steel metal sheets that are formed into a cylindrical shape, then welded
along the seams. Hemispherical or elliptical tank heads are welded to the barrel to form the tank.
See Figure 8-20.
All MC-331 cargo tanks have relief valves; temperature, pressure and liquid level gauges; liquid
and vapor transfer lines and valves; and remote emergency valve controls.
Openings for transferring propane liquid and vapor are located in the bottom of the tank, either in
the underside of the shell and/or in bottom half of the rear head. Openings for the pressure relief
valves are located in the top of the tank.
Most propane cargo tanks are uninsulated and are required to have the upper two-thirds of the
tank painted white, aluminum, or a similar heat reflective color.
INCIDENT ACTION PLAN
Tactical Objectives
The primary tactical objective for this operation is to control or stop the propane liquid from
escaping the bottom of the tank truck. The secondary objective is to maintain site safety until the
propane in the damaged tank truck can be transferred to another tank truck.
Methods of Leak Control
The first initial action by the Incident Commander should be to implement site management
procedures, (e.g., isolate the area and deny entry, remove bystanders to a safe area, and
establish Hazard Control Zones.)
A call for technical assistance from the propane transport company should be made as soon as
possible. The transport owner should be briefed on the nature of the problem so that the proper
personnel and resources are dispatched to the scene.
Firefighters in full protective clothing and SCBA should deploy hoselines to disperse and dilute
the flammable gas away from and off of the bridge. Two 1-1/2 or 1-3/4 inch hoselines flowing 100
gpm or higher are recommended; however larger hoselines or master streams may be
necessary. A combustible gas indicator (CGI) should be used to determine the effectiveness of
hoselines in dispersing the gas.
If temperatures are expected to rise, water for container cooling as well as vapor suppression
should be provided.
Given that the tank truck's piping and valves are severely damaged and there is a visible propane
liquid leak on the bottom half of the tank, the cargo tank will have to be unloaded. Considerable
time may pass until a compatible MC-331 is available on scene for product transfer. In the
meantime, some attempt should be made to slow down or stop the leaking propane on the
damaged tank.
Additional factors to consider for this operation include:
• When the ambient temperature is above 90° F, hose water fog played on
the top of the tank can be effective in keeping the tank's shell cool. The
average temperature of hydrant water is 52° F. When ambient
temperature is below 40° F water will warm the tank.
• Combustible gas indicator (CGI) readings should be taken throughout
the incident to ensure that hoselines are effective in dispersing flammable
vapors.
The Incident Commander has three tactical options for leak control:
1. Fiberglass Wrap&emdash;A vapor leak can be stopped with the use of
a commercial fiberglass wrap material known as "Stop It"™. Field
experience has shown that fiberglass wrap kits work successfully on most
propane vapor leaks. The roll of Fiberglass Wrap is wetted and wound
around the damaged pipe or valve. When the wrap sets up it will stop a
vapor leak up to 200 psig. However, if there is a liquid leak producing a
vapor cloud that can be seen, these kits will not work.
2. Freeze Wrap&emdash;A liquid leak can sometimes be sealed off by the
use of a freeze wrap which forms an ice patch over the leak area. A towel
or fabric wrap is wetted, then wrapped around the leaking valve or pipe.
The wet cloth will freeze due to the propane liquid's very low temperature.
CAUTION: Firefighters must wear heavy neoprene gloves suitable for
working with low temperatures to avoid frostbite. Cloth or leather gloves
can absorb liquid propane and result in injury. Freeze wraps should be
monitored for reapplication. See Figure 8-22A.
3. Water Injection&emdash;Propane has a specific gravity of .504 (water =
1), so water will sink to the bottom of the tank. Looking at the problem
from a weight perspective, propane liquid is in the bottom of the tank and
weighs 4.20 pounds per gallon. Water weighs 8.34 pounds per gallon. If
water can be injected into the tank, it will sink to the bottom of the tank
and form a layer of water which will leak out of the damaged valve or pipe.
If the flow of water into the tank can be maintained, flammable vapors will
not be produced and the transfer of product can be conducted under safer
conditions. In some cases the leaking water will come into contact with the
cold metal on a valve or pipe and form an ice patch. Fires on the lower
half of a propane tank have been extinguished in the same manner.
WARNING: When using the water injection method, special consideration
must be given to the possibility of creating a hydrostatic condition which
will pressurize the propane tank and activate the relief valve. It is vital that
the person operating the water injection nozzle be prepared at all times to
shut down the line. This technique should only be attempted by or under
the supervision of an experienced propane or container specialist. If the
support of qualified personnel is not available, the tank should be
protected by unstaffed monitors and emergency responders should switch
to a defensive posture.