Incident Overview


A broken gas line near the bottom of a 1,000 gallon ASME stationary propane tank in agricultural service has resulted in a gas-fed propane fire. The fire is impinging on the outside shell of the tank below the liquid level. The tank's relief valve is functioning intermittently and a plume of gas has ignited and is burning above the relief valve.

The nearest exposure is a horse barn 75 feet away from the tank.

 

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Summary of Tank Construction Features


ASME stationary tanks can be found at homes and at commercial, industrial, and agricultural facilities. Stationary tanks can also be found at service stations for refilling recreational and motor fuel tanks. Stationary tanks are normally filled from a bobtail truck.

Most stationary tanks are built by welding two heads to a barrel. Their capacities typically range from 250 to 2,000 gallons, with most domestic tanks being less than 1,000 gallons.

ASME stationary tanks are designed for different working pressures depending on their intended service. The normal working pressure for stationary propane service is 250 psig.

Fittings for valves under 2,000 gallons capacity are normally threaded. Threaded attachments are commonly 1/4 inch to 2-1/2 inch female normal pipe thread (NPT) with some special flanges for liquid level gauges. Openings are normally located on top of the tank.

 

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Incident Action Plan


Tactical Objectives

  1. Cool the outside of the stationary tank's shell at the point of flame impingement so that the internal tank pressure drops to the point where the relief valve closes and the tank valve can be manually closed.

  2. Protect exposures, extinguish any ground or structural fires, and check for extension of the fire.

Methods of Extinguishment

A 1,000 gallon propane tank requires a minimum continuous flow of 100 gallons per minute (gpm) to adequately cool the tank shell. This can be provided through a 1-1/2 or 1-3/4 inch attack line flowing 100 gpm or higher.

Two handlines are recommended to attack and extinguish the fire. The first line should be placed in service as soon as possible and be played evenly on the tank shell to keep it cool while the second line is being deployed. A third back-up line is recommended to protect the attack crews and protect exposures. The back-up line should be in service before the attack begins.

Crews should continue cooling the tank shell until the relief valve closes. Once the relief valve has closed, both attack teams will simultaneously advance toward the burning tank from the side of the tank, under the protection of fog patterns (a.k.a. power cones). Nozzle patterns should be adjusted so that they overlap and provide the broadest possible protection as crews advance.

When the tank is reached, a designated crew member should close the valve on the tank. This will isolate the broken gas line. Residual gas inside the broken line will burn off quickly and the fire will be extinguished.

 

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Additional Factors


Additional Factors to Consider for this Operation Include:

  1. If a fixed mounted master stream such as a deck gun on a pumper can be placed in service immediately, it should be directed onto the burning tank until handlines are deployed.

  2. It is important that nozzles on handlines match so that there is a constant flow and nozzle patterns are compatible. If variable gallonage nozzles are being used and are being supplied from two different pumpers, the driver/operators must ensure that they are maintaining a coordinated fire flow.

  3. The back-up handline should be supplied from a water supply which is independent of the primary attack line in case the primary handline loses its water supply.

  4. In rural water supply operations, it is important that pumpers be adequately resupplied so that water supplies are not expended once the initial attack begins. Water supplies obtained from portable drafting basins and shuttle tankers must be able to meet the required fire flows and be capable of supporting the fire attack. Request additional water resources in accordance with local practices early in the incident. If you doubt that the fire attack can be supported with an adequate water supply, switch to a non-intervention strategy.

  5. Heavier hose streams and fire flows may be required if the fire has communicated to the structure (e.g., in this scenario, the barn is a primary exposure).

  6. Stationary tank valves are right-to-tight, left-to-loosen. Make sure you are turning the valve off, not on.

  7. If copper gas lines are damaged, crimp off the line with pliers after the tank\'s valve has been closed. Another alternative is to plug the valve using a left-handed thread POL plug.

  8. Continue to cool the tank until well after the fire has been extinguished. The initial application of water to the super-heated steel will generate steam. When steam no longer appears it is an indication the situation is coming under control. The metal surface should be cool enough to touch.

  9. The area around the tank and inside the adjacent structure should be monitored for flammable gas using a combustible gas indicator (CGI).

 

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 Incident Map


This is a top-perspective view of the incident area. Its purpose is only to get the general idea of the incident and surroundings.
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 Incident Video


In this section, we present an animated version of the incident.