Incident Overview


A propane leak has occurred under the dome cover of a 1,000 gallon ASME stationary aboveground tank. The propane gas is drifting slowly away from the tank and is settling in the area between the tank and the wall of a factory, 25 feet away from the tank. An adjacent 1,000 gallon storage tank is next to the leaking tank but is not involved.

A church, grocery store and gasoline station are across the street. The 911 caller informed the emergency responders that they saw children playing around with the tank just before the leak occurred.

The incident has occurred in the early morning, and the temperature is 48° F. The weather forecast calls for steadily increasing temperatures to 70° F by 3:00 pm.

 

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Summary of Cylinder Construction Features


  1. 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.

  2. 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 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 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. The primary tactical objectives are to control ignition sources and disperse and dilute the flammable vapors being released from the aboveground tank using fog streams from hoselines.

  2. The secondary objective is to secure the leak and repair the damaged container with the assistance of the local propane dealer.

Methods of 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 local propane dealer should be made as soon as possible. The dealer should be briefed on the nature of the problem so that the proper tools and parts are dispatched to the scene.

Firefighters in full protective clothing and SCBA should deploy hoselines to disperse and dilute the flammable gas away from the primary source of ignition. Two 1-1/2 or 1-3/4 inch hoselines flowing 100 gpm or higher are recommended. Fog nozzles should be placed on narrow angle fog patterns to aid in dispersing the flammable gas. The placement of the hoselines should be such that the propane gas is directed away from the wall of the factory.

  1. A Combustible Gas Indicator (CGI) should be used to determine if hoselines are effective in dispersing the gas. Readings should be taken with potential exposures in mind; (e.g. downwind areas where severe exposures could exist, inside occupied areas or locations where the gas could travel, downhill, below grade and other confined areas.)

    1. A reading should be taken downwind to see if the gas is dispersed. When Combustible Gas Indicator (CGI) readings indicate levels of 10% of the lower flammable limit or greater, additional charged handlines should be in place as a precautionary measure.

    2. A reading should be taken outside and inside the building to determine if propane gas has migrated into the building. If CGI readings exceed 10% of the lower flammable limit, the entry team should withdraw and ventilate the building using positive pressure ventilation. Ventilating the interior space will lower the level of flammable vapors inside the structure.

    3. When Combustible Gas Indicator (CGI) readings indicate detectable levels of flammability, responders should not activate potential ignition sources (e.g. light switches, garage doors, or interior heating and air conditioning or ventilating equipment).

    4. Other readings should be taken to assure that the propane gas is not drifting towards other exposures, structures or hazards.

    5. Propane gas dissipates rapidly but may settle in low unventilated areas. Readings should be taken in sewers, manholes, or below grade areas.

  2. Flammable Atmospheres-OSHA and most national consensus standards consider a flammable atmosphere containing concentrations of 10% or less of the lower flammable (explosive) limit (LFL) as acceptable for conducting rescue operations.

    1. Areas with flammable concentrations of 10 to 20% of the LFL are considered hazardous and should not be entered by rescue teams unless they have proper PPE.

    2. As flammable readings rise above 20%, the level of risk to responders also rises. Rescue personnel operating in flammable concentrations of 50% of the LFL or greater should immediately leave the hazardous area.

  3. Additional hoselines are recommended to back-up the team dispersing the flammable gas and to stand-by to protect exposures in case of accidental ignition.

  4. A repair crew can gain access to the dome cover and valve on the top of the tank. A qualified propane repair person with proper protective clothing and equipment can determine the problem and make emergency repairs by either shutting the valve or replacing the damaged equipment. All emergency repair operations must be done under the protection of wide angle fog from a hoseline dedicated to the protection of the repair crew. Once the replacement parts are in place the area should be checked with a CGI before the hoselines can be shut down.

 

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Additional Factors


Additional Factors to Consider for this Operation Include:

  1. Hoselines should be positioned so that they are effective in dispersing the flammable gas.

  2. Where possible, the back-up or standby hoseline should be supplied from a water supply which is independent of the primary hoselines dispersing flammable vapors in case the primary handline loses its water supply.

  3. Before leaving the scene the interior of buildings in the area should be checked again for flammable vapors using a Combustible Gas Indicator (CGI). There should be no reading on the CGI.

 

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 Combustible Gas Meter


This is an interactive combustible gas meter. Move your mouse or finger (touch device) over the leak area to view the Gas-in-Air percentage change.
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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.