Module 9: Control Techniques - International Association of Fire ...

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IAFF Training for Hazardous Materials: Technician© Student Text MC 312/DOT 412 tankers use gravity and/or internal tank pressure to off-load. Pressure in piping may be near 75 psi. Leaking corrosives can cause additional chemical stress to the outside of the tank, piping or valves. Activity Dome Cover Leaks A dome cover may become loose and leak as a result of a rollover. Dome cover clamps are used to stop this type of leak. Cargo tanks, when not on their wheels, may be unstable. They may also have suffered physical container damage. If other damage to the container is not a problem and the tank is stable, you can apply the appropriate size dome clamp. Obviously, you will not be able to upright the tank. Physical hazards of the product become a serious concern in clamp operations because you will most likely have considerable product contact during approach and containment activities. Slip hazards will almost always be present. Access may also present a problem. If the tank has rolled over, the covers may be beneath the tank. If the tank has not rolled over, you may have to use a ladder to safely access the dome cover. Tears/Irregular Holes/Punctures Breaches in cargo tank bodies can be caused by vehicular accident, rollover, or impact with other objects such as forklifts. Depending on the location of the breach, releases can range from 2,500 gallons in a single compartment to over 7,000 gallons from multiple compartments. These types of leaks are commonly handled by hazardous materials teams. Most of these breaches can be controlled with the same methods used on smaller liquid containers like drums. However, you must plan for potential hazards of a large volume release because of the size of the containers. 9-30 Module 9: Control Techniques
Student Text IAFF Training for Hazardous Materials: Technician© Although control techniques for drums are similar for tanks, tank breaches may be larger or require more control materials. You can purchase bandages developed specifically for use with cargo tanks or large quantities of absorbents. If the leak is above the product line, containment will be relatively easy. You will be able to apply the appropriate plug, patch and/or bandage with minimal product contact. As always, determine container integrity, especially in the area of the patch or plug. This may be difficult, however, depending on the size of the tank and location of the breach. If the leak is below the product line, significant product release may be occurring during containment operations. You may not be able to apply plugs and/or patches because of the force of product flow caused by head pressure. Containing leaks of large volume flow is difficult at best, and will result in contamination of the entry team. Another problem that may develop is the product’s reaction with the outside container. Corrosives tanks are generally stainless steel or steel construction lined with butyl rubber or some other resistant material. If an MC 312/DOT 412 has had a breach in that liner, the corrosive will contact the steel outside the container and possibly work its way between the liner/tank interface, seriously reducing the structural integrity of the container. Vents/Relief Valves/Rupture Disk Leaks Vents are designed to allow normal vapor release. They are engineered to prevent leaks of liquid product if there is a rollover. If liquid is being released from a vent, it has probably failed. You must consult with container specialists and assess the risks fully to determine why the vent is leaking and the ramifications of containing the leak. Relief valves are designed to operate in case a container is overpressurized. MC 338 cargo tanks’ (cryogenic carriers) relief valves or vents normally operate as the product inside vaporizes, increasing pressure inside the vessel. If the cargo tank is not a cryogenic carrier and the relief valve is operating, you should find out why. Do not try to contain Module 9: Control Techniques 9-31
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