LP-Gas Tank Explosion Kills Two Volunteer Firefighters (Carthage, Illinois - October 2, 1997) » Building and Fire Prevention Codes

The farm is located in Hancock County, which would have code review and enforcement authority. In addition, the State of Illinois and the Office of State Fire Marshall have enacted laws and regulations for liquefied petroleum gas storage and use. The state regulations acknowledge that compliance with National Fire Protection Association (NFPA) Standards shall be accepted as compliance with state regulations.

The analysis that follows makes use of NFPA Standard No. 58, Standard for the Storage and Handling of Liquefied Petroleum Gases and National Propane Gas Association (NPGA) documents #500-93, Safe Use of Propane with Crop Dryers and NPGA #613-92, Guidelines for Manifolding Liquid Withdrawal ASME Containers not Exceeding 2000 Gallon W.C. at Construction Sites. NFPA Standard No. 54, National Fuel Gas Code does not apply to crop dryers or to the LP-Gas fueled tractor.

According to NFPA Standard No. 58, the two 1,000 gallon capacity tanks should have been located at least 25 feet from any building. The purpose of this distance is to provide exposure protection for a fire at either the tank or the building. A building fire would not immediately threaten the LP-Gas tank and a fire at the LP-Gas tank connection or relief valve would not immediately start the building on fire. Another reason for the separation distance is to minimize the potential for escaping heavier than air LP-Gas to enter the building potentially finding an ignition source.

The tanks should have also been positioned with at least three feet of space between the two tanks. This space allows access for water streams to cool the tank surfaces and for personnel to reach the valves on the top of the tank. Another important separation distance is between a gas discharge point on the tank and potential ignition sources such as the grain dryer and tractor. NFPA Standard No. 58 indicates that at least ten feet should be provided. Potential gas discharge points are the fill connections, the pressure relief valve, and hydrostatic relief on liquid piping. The NPGA also recommends that grain dryers be shut down during LP-Gas tank filling unless the distance between the dryer and the tank is over 50 feet.

NFPA Standard No. 58 limits flexible hoses to 36-inch maximum length. The LPGas supply hose from the tank to the dryer exceeded the maximum and should have been replaced with Schedule 80 pipe and high-pressure fittings. The heavy piping and fittings are needed because the line contains liquid LP-Gas and the operating pressure could exceed 250 psi. The piping between the tank and the dryer/tractor would also need to be protected from mechanical damage. The pipe should be buried, with adequate corrosion protection, or suspended on supports above ground. The liquid supply piping would also need an excess flow valve, shut-off valve, and a hydrostatic relief valve. The excess flow valve is to stop liquid discharge if the line fails catastrophically. The shut-off valve is the manual means to stop the LP-Gas flow or to isolate the line for other work. The hydrostatic relief valve is intended to protect the line if the trapped liquid expands as its temperature increases. The excess flow valve and hydrostatic relief valve were needed on the liquid line regardless of the line’s construction material.

To comply with NFPA Standard No. 58, the pipe lines used to manifold the two 1,000 gallon tanks should have been constructed of Schedule 80 pipe with extra heavy fittings because the pipe could experience pressures over 250 psi during normal operation. The process of manifolding the two tanks involves separate connections between the vapor space and the liquid space in each tank. Two separate pipes are needed to ensure that the liquid level in each tank remains balanced as internal pressure is equalized in the two tanks. The liquid manifold line could have made use of bottom outlet connections on each tank. Alternately, tanks manufactured after July 1, 1961 have liquid top outlets, which could have been used.

The liquid manifold piping would need an excess flow valve and manual valve at each tank and a hydrostatic relief valve in the line because of the possibility of trapped liquid. The vapor manifold line would also need an excess flow and manual valve at each tank.

The remains of various LP-Gas hose connections were gathered after the fire. A number of the fittings used to attach the hose were not industry approved for use with LP-Gas hose. Substandard hose fittings included stainless steel bands with adjustable screws. It is suspected that these connections did not have sufficient pressure rating for the LP-Gas liquid service.

The omission of a vapor manifold connection between the two tanks did not allow the liquid levels to equalize or balance in the two tanks. As a result, the fire heated the west tank and pushed liquid into the east tank until it was 100% liquid filled. The east tank then failed at its weakest point, the weld seam. The east tank’s relief valve may have been unable to reduce the pressure fast enough or failed to operate effectively.

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