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Field product removal methods are those techniques used for removing the contents from a damaged or overloaded rail tank car or cargo tank (tanker truck) in the field. These methods include:
In addition, hot tap is a method for gaining access to the contents of a tank car or tanker truck when damage to the valves and fittings precludes normal access. Hot tap is used in conjunction with other field product removal methods (i.e., transfer, flaring, or venting).
Each field product removal situation is unique. Decisions are best made by those at the scene who are knowledgeable about the product and the equipment involved. Under no circumstances should these type of operations be attempted without a thorough understanding of the products involved. The preferred situation would be to have a representative of the product manufacturer participate in the transfer/removal operation.
The product removal methods are considered outside the legitimate responsibility of the local emergency responder; however, oversight of the planning and implementation of these methods is within the realm of responsibility of local emergency response agencies.
The following section includes a brief overview of field product removal methods used with tank cars. For detailed recommendations, refer to the document: "Field Product Removal Methods for Tank Cars," FRA/ROD/92-27, Final Report, prepared by the Association of American Railroads/Transportation Test Center, February 1993. Although we did not illustrate them in this article, field product removal methods from cargo tanks would be conceptually similar to those used with tank cars.
Note: The intent of this article is to broaden the knowledge of people who may be faced with emergencies for which these methods are appropriate. Since no amount of technical knowledge is a substitute for practical experience, emergency responders should never take actions for which they do not clearly understand what the outcome will be. In addition, persons who expect to engage in these situations must be qualified with specialized training.
Overview
Typically, transfers in the field are distinguished by the basic equipment used
to move the contents from the damaged or overloaded tank car. Gas transfers can
be accomplished in the field using one of the following methods:
For an overloaded or damaged tank car where an increase in internal pressure is acceptable:
For an overloaded or damaged tank car where no increase in internal pressure is acceptable:
Gas Transfer Using a Vapor Compressor This transfer method uses a vapor compressor to move the contents of a damaged or overloaded tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). The vapor compressor creates a positive pressure differential by pulling the vapors from the receiving tank, compressing them, and forcing them into the damaged tank car. The pressure in the damaged tank car pushes the liquefied gas into the receiving tank. |
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Gas Transfer Using a Liquid Pump This transfer method uses a liquid pump to move the contents of a damaged or overloaded tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). Pressure is equalized between the damaged tank car and the receiving tank by connecting a hose to the vapor valves of each car. Then, the product is pumped from the damaged tank car to the receiving tank. |
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Gas Transfer Using a Liquid Pump and a Vapor Compressor This transfer method uses a liquid pump to move the contents of a damaged or overloaded tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). The rate of transfer is accelerated by using a vapor compressor to create a pressure differential by withdrawing vapors from the receiving tank, compressing them, and forcing them into the damaged tank car. The pressure in the damaged tank car helps keep the pump primed. |
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Gas Transfer Using an Inert Gas This transfer method uses an inert gas compatible with the product (e.g., nitrogen or carbon dioxide) to move the contents of a damaged tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). The inert gas creates a pressure differential and pushes the liquid into the receiving tank. Vapor from the receiving tank may need to be vented or scrubbed. |
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Gas Transfer Using Product Vapor Pressure and Flaring This transfer method uses the vapor pressure of the contents to move the contents of a damaged or overloaded tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). The vapor pressure in the damaged tank car pushes the product into the receiving tank. The pressure differential between the damaged tank car and the receiving tank is maintained by burning off vapors from the receiving tank at the outlet of a flare pipe. The pressure in the receiving tank is kept as low as possible. The transfer method is accelerated by introducing an inert gas into the damaged tank car as the pressure drops. This transfer is used only for flammable gases. |
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Overview
Because of the wide range of products, valve and fitting arrangements, and
situations, it is impractical to specify all of the combinations of equipment
that may be used to perform a liquid transfer.
Persons contemplating a liquid transfer must make their own equipment list based upon consultation with the shipper, their own analysis of the appropriate methods, and the equipment available. Other considerations include properties of the product, and of other nonmetallic parts (gaskets, seals, etc.).
Liquid Transfer Using a Liquid Pump This transfer method uses a pump to move the contents of a damaged tank car to a receiving tank (e.g., a tank car, cargo tank, or portable tank). Pressure may be equalized between the damaged tank car and the receiving tank by connecting a hose to the vapor valves of each car, or by venting to the atmosphere. Then, the product is pumped from the damaged tank car to the receiving tank. |
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Overview
Product-Removal can be used by the responder to reduce pressure in a tank car,
dispose of a product, or gain access to the contents of a tank car when
conventional transfer methods are not feasible due to damage, safety
constraints, or other factors.
Vapor Flaring Vapor flaring is the burning of vapors of a liquefied flammable compressed gas at the outlet of a flare pipe as they exit the pipe. A vertical or horizontal flare pipe can be used. |
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Liquid Flaring Liquid flaring is the vaporizing of flammable liquid product and burning the vapors at the end of a horizontal flare pipe. A pit is used to contain any product which is not completely burned. |
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Venting Venting is the process of releasing non-flammable, liquefied compressed gas vapors into the atmosphere. This release can be direct or, in case of toxic products, indirect through an appropriate treatment system. Typically, venting is done with nonflammable gases. |
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Vent and Burn Vent and burn is the process of using explosive charges to cut a hole (or holes) in a tank car and allowing the product to flow into a pit for burn-off. Because of its inherent risks, vent and bum is considered to be the last viable option for product removal. |
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Hot Tap The hot tap is a method of providing access to the contents of a tank car when damage to the valves and fittings precludes access to the contents. Once the hot tap is completed, transfer, flaring, or venting can take place. Hot tapping involves the welding of a threaded nozzle onto an undamaged section of the tank that is in contact with the liquid. A liquid high-pressure ball valve is attached to the nozzle. A hole is then drilled through the tank with a special drilling machine. The drilling machine is equipped with seals that prevent loss of product during the drilling operation. Liquid hoses or pipe can be attached to the valve/outlet. |
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