Propane Gas Barbecue Grill Fire: Expect a BLEVE

By Scott Joerger

It was a perfect night to grill shish kabobs in the propane barbecue grill on the back deck of the house. The external temperature was approximately 80°F, and the relative humidity and winds were low. The homeowner had a new barbecue grill with a big cabinet below the grill. The cabinet was perfect for storing grilling tools and two 20-pound liquid propane tanks so he would never run out of gas in the middle of grilling. He had no idea of how dangerous it is to store a propane tank inside a compartment below the grill.

The back deck was constructed of wood and was elevated about five feet above a sloped gradient backyard. The deck was the same level as the first floor of the house and accessible by two glass doors from the house and from stairs off the backyard. The house was Type V modern wood construction with vinyl siding exterior. Everything was going right until the homeowner/chef depleted the gas in his first propane tank and he quickly changed over to the second full 20-pound liquid propane tank in the cabinet.

When he reignited the grill, he immediately noted flames coming from above the cabinet and below the grill. He tried to open the door to the cabinet to shut down the flow of gas, but he was unable to get his hand near the shutoff because of the flames and heat. His wife, standing by the glass patio doors inside the house, saw his predicament. She yelled that she was calling the fire department. The homeowner went inside to evacuate their children to the front yard. The wife phoned 911 from her cell phone as they evacuated with the family. Both report that the call to 911 was about a minute or two after ignition.

The Incident

The phone call was received at the 911 Center at 1829 hours and dispatched by 1831 hours to the Pittsford (NY) Fire Department. The first engine was on scene at 1835 hours. The lieutenant reported nothing showing from a large two-story wood-frame house. On investigation, he found the gas grill involved in flames and the deck and railing behind the grill burning as well. The grill was about six feet from the rear of the house, and the vinyl siding was melting and sagging in the area closest to the grill. By 1838 hours, the lieutenant and two firefighters had stretched a 1¾-inch handline to the rear lawn. They began to mask up and prepare the handline about 20 feet away from the fire, which was above them on the deck. A second lieutenant also called for a second handline to the interior. The exterior handline crew could hear the tank’s pressure relief valve whistling, but because the tank was inside a cabinet, they could not see the distinctive flame coming from it.

As they called for water, they heard the pressure relief valve make a higher pitched whistle; the lieutenant had the crew back off to a safer position. As his crew shifted, the propane tank exploded. A fireball set afire the house’s exterior and plastic deck chairs. Shrapnel from the tank and grill were sent up to 40 feet in all directions. The large top of the grill was blown away 25 feet and into the homeowners’ pool. The cylinder valve hand wheel to the propane tank blew through the glass door window into the house and penetrated three walls, finally lodging into the front wall of the house. The second empty propane tank was blown away and landed in the exact spot from where the handline crew had just retreated and caused the grass to burn. The propane tank that failed was projected downward and created a hole in the deck floor about two feet in diameter. The tank broke through one- by six-inch pressure-treated wood decking and two- by eight-inch pressure-treated supports that were 16 inches on center. The tank blew into the dirt and ground below the deck.

(1) The burning propane barbecue grill was on the deck. The fire spread to the house and deck. The BLEVE propelled a large section of the 20-pound propane tank downward through the wood deck. (Photo by Tim Hyland.)
(1) The burning propane barbecue grill was on the deck. The fire spread to the house and deck. The BLEVE propelled a large section of the 20-pound propane tank downward through the wood deck. (Photo by Tim Hyland.)

None of the firefighters was injured in the explosion. Both lieutenants quickly verified their crew’s accountability and reported this to Command. With the first handline charged with water, the exterior crew immediately went to work to extinguish fire from the house and the deck. The fire was investigated. It was determined that the fire developed from a gas leak in the area of the gas point of the connection to the propane tank (photo 1).

The explosion of the 20-pound propane tank was a boiling-liquid, expanding-vapor explosion (BLEVE). This particular BLEVE had the basic characteristics of most BLEVEs-overpressure blast, fireball, and tank fragments propelled away. It resulted from the external fire fueled by a gas leak. The gas leak resulted from an improper connection of the gas hose to the second tank when the homeowner switched from the first tank to the second. The fire immediately began heating the tank and the liquid propane inside. A filled propane tank consists of two inside areas-the liquid portion and the vapor space. Even a full 20-pound propane tank will always have a vapor space above the liquid portion.

(2) The top of a 20-pound propane tank showing the pressure-relief valve, the cylinder valve hand wheel, and the gas point of connection. (Photos 2-5 by author.)
(2) The top of a 20-pound propane tank showing the pressure-relief valve, the cylinder valve hand wheel, and the gas point of connection. (Photos 2-5 by author.)

There are two reasons vapor space exists in a full propane tank. First, 20-pound tanks are designed big enough to hold more than 20 pounds of liquid propane. Second, most refill companies will not fill the tank with 20 pounds of liquid propane because of safety concerns related to overpressuring.

The fire caused the liquid portion inside the tank to become superheated, which pressurized the tank and caused the relief valve to open. The relief valve was designed to open and allow excessive pressurized propane to vent out the top and above the tank, or vessel (photo 2). This pressurized propane vapor ignited inside the confined cabinet, radiating and conducting heat back onto the tank. The relief valve is intended to vent away from upright propane tanks so that when the vapors ignite, the flames burn up and away from the tank. Intense flames were concentrated inside the cabinet up toward the top of the tank at the vapor space.

(3) This propane gas barbecue grill has the propane tank fully enclosed in a cabinet.
(3) This propane gas barbecue grill has the propane tank fully enclosed in a cabinet.

A fire impinging on the vapor space is an immediate, serious concern. Flames cause the vapor space of the tank and the tank wall to heat up rapidly as opposed to flames impinging on the liquid portion. The liquid portion of the tank is able to absorb heat from a fire and transfer it away from the tank wall. As pressurized propane is vented out of the relief valve, the area of the vapor space becomes larger as propane is depleted from the tank. From this incident, as the fire continued to burn, the increase of heat to the tank caused the noise from the pressure relief valve to change and become higher pitched. This indicated an increase in tank pressure and the relief valve’s inability to release this pressure. At this point, the top area of the tank in the vapor space tore apart and exploded as a result of this pressure and the weakening of the tank wall from the external flames to this area.

The BLEVE occurred approximately 10 minutes from ignition, just after the firefighters arrived on the scene. The firefighters had never seen a propane tank fire inside a cabinet below a barbecue grill (photo 3). Older propane gas grills had the 20-pound tank open and below the grill (photo 4). Fires that occurred around the gas connection allowed much of the heat to be dissipated into the air. Therefore, the relief valve usually does not activate with this type of fire. If it does activate, flames are directed up and away from the tank, assuming the tank is upright and in its proper location on the grill.

(4) This propane gas barbecue grill does not have the propane tank enclosed.
(4) This propane gas barbecue grill does not have the propane tank enclosed.

When the relief valve activates, the objective is to apply water from a safe position to cool the tank. When the propane tank is not inside a cabinet, it will not be difficult to apply water from a handline to cool the tank and then to obtain access to the gas shutoff. This is not the case with a cabinet grill. Because the tank is enclosed inside the cabinet, it is difficult to apply water with a handline. There may be a chance if the cabinet door is open, but only if the firefighter is careful enough to direct water is such a way as not to cause the door to close. You can also apply water to the tank if the cabinet door is not completely enclosed. Not all cabinet grills are completely enclosed. Some are missing back panels; others may have no back and side panels (photo 5).

Fires in barbecue gas grills are common. The fire can occur on the grill, in the pan below the grill, in the area below around the burners and gas burner keys, and in the area of the gas hose by the point of connection to the cylinder. These fires will grow quickly if the extremely flammable propane gas from the tank is free flowing. The fire will then become very dangerous if the pressure relief valve activates as even more pressurized propane vents out. When all of this is enclosed in a cabinet, a BLEVE is likely.

(5) This propane gas barbecue grill cabinet is not fully enclosed. It is open in the rear.
(5) This propane gas barbecue grill cabinet is not fully enclosed. It is open in the rear.

Tactics for Propane Tank Barbecue Grill Fires

Below are some suggested tactics to assist with all types of propane tank barbecue grill fires.

  • On arrival, ensure a water supply, and immediately stretch a handline. Keep the uncharged line toward the front of the building so that you can move and deploy it quickly when you determine the best way to access the fire.
  • Size up the fire with information from people on the scene. Begin by verifying the size of the propane tank and ruling out the use of natural gas. Natural gas is also commonly used for grilling and should be handled by shutting off the flow of gas at a remote shutoff. With propane, the 20-pound liquid propane tank is the common size for a barbecue grill. However, portable liquid propane tanks come in many sizes, such as five, 11, 30, 40, 50, and even 100 pounds! Also, ask about the number of tanks with propane product inside that are involved. Many people have more than one propane tank; some cabinets are built to store two 20-pound tanks. Do not be overly concerned about empty propane tanks in the area of the fire. Empty propane tanks, if truly empty, will not build up pressure when exposed to fire the way a tank with liquid propane inside will. Finally, ask if there are any civilians nearby or inside nearby exposures. Immediately remove them to a safe area.
  • Visually size up the fire area from a safe position. Determine the best and safest way to stretch the handline. Take a look at exposures, what is burning, and access to the fire area. Listen for the whistle of the relief valve, and note where the large flames from the relief valve are venting. From the incident previously described, the whistle from the pressure relief valve changed to a higher pitch just prior to the BLEVE. This should not be interpreted as an indication of when a BLEVE will occur. Anytime the pressure relief valve is activated and the pressurized propane is burning, immediately prepare for a BLEVE. Also, anytime these flames are enclosed inside the cabinet and radiating heat back to the tank, expect a BLEVE. This is the time to call for additional units, including a rapid intervention crew, if needed.
  • Develop an initial action plan (IAP), and wear full protective gear including self-contained breathing apparatus. The IAP should always have crews begin operating in a safe area. Shrapnel from an explosion could travel some distance. It is important to protect your entire body and face. Also, if a BLEVE occurs, it may set an exposure on fire, and the handline crew will need to move in and extinguish this. This exposure is likely to be a house.
  • Consider allowing the tank to BLEVE or the fire to burn itself out. With a serious fire in which the pressure relief valve has activated and is burning and there are no exposures threatened by the BLEVE, pull back to a distant, safe location. Allow the BLEVE to occur or the fire to burn itself out. Have a handline standing by for safety and to deploy after the BLEVE to extinguish any remaining fire. Most times, this will not be an option because the grill and fire will be near the back of a residential building.
  • If a fire attack is needed, stretch the handline to a safe distance (as far away as possible) and immediately start to flow water to cool the tank and extinguish fire. The objective is to operate a 1¾-inch handline using the reach of the straight stream so that water cascades onto the tank, grill, and fire while flooding the area. Cool the tank around the top first and then extinguish exposure fire around the tank and grill. If the cabinet door on the grill is closed, try moving while flowing water to a side or the back of the grill. The grill cabinet may not be completely enclosed and may be open from the side or the back. Another advantage of this safe-and-away location is that you do not want a pressure stream of water to move the grill or dislodge the tank. Wind conditions will be a factor. Work with the wind for optimal application of water, or change to a larger hoseline to maintain a safe, distant operating location.
  • Stretch additional handlines as determined by your ongoing size-up and IAP. Another handline will be needed to begin flowing water from a different position if access to the tank is difficult. The line is needed to assist with cooling the tank and flooding the area. Additional handlines might also be needed here and for exposures.
  • Stay alert for a BLEVE, and reevaluate the IAP. Cooling the tank with water may not be sufficient. The situation should improve quickly if you adequately apply water to the tank and the surrounding fire. Reevaluate and change the IAP as needed. If a BLEVE occurs, conduct a personnel accountability report for all personnel operating to ensure safety, and then extinguish the exposure and any remaining fires. Size up, and take appropriate action if additional full or partially full propane tanks are discovered.
  • If the fire is extinguished, continue flowing water. Unignited propane gas flow from the tank is a problem. At 60˚F, it is 11⁄2 times heavier than air and can collect and travel to low areas. It will easily ignite. Continue the flow of water to the area, and begin to move the stream around attempting to disrupt this flow and disburse gas to an open area. If possible, move up to the tank with handline protection. Try to shut off the flow of propane gas at the cylinder valve hand wheel. A pair of locking pliers may assist in turning off the flow of propane if the cylinder valve hand wheel has been damaged by the fire. Once the flow of gas is stopped and the fire is out, use a combustible gas meter to detect a buildup of gas into adjacent areas and buildings; remove any buildups.
  • Conduct a critique of the operation with personnel before leaving the scene. This situation can be dangerous; review it for safer operations.

The first time many of us ever heard of a BLEVE was as a new firefighter during initial training. It usually involved a hazardous materials incident with a large tank, like a rail car. Most instructors said that an incident involving a BLEVE would be a dangerous and large event that rarely occurred. This is not the case today for a barbecue grill fire when the fire is inside the cabinet storing the propane tank.

References

http://www.efcog.org/wg/sa/docs/minutes/archive/2000%20Conference/papers_pdf/roberts.pdf.

http://www.propane101.com/index.htm.

http://www.ehow.com/how_7836662_connect-propane-tank-gas-grill.html.

http://www.emptygrilltank.com/tank-sizes-and-specifications/.

http://www.propanesafety.com/uploadedFiles/Safety/Workforce_Training_programs/Propane_Emergencies_(PE)_Program/MTK_02-Properties.pdf.

SCOTT JOERGER is a captain with Engine 5 of the Rochester (NY) Fire Department. He is also training captain and former chief of the Pittsford (NY) Volunteer Fire Department. He has worked as a wildland firefighter with the U.S. Forest Service in Oregon. He has an associate degree in fire protection and a bachelor’s degree in management.

BLEVE : Facts, Risk Factors, and Fallacies
PROPANE EXPLOSION: A CASE STUDY
Hazmat: Initial Actions and Chemical Assessment

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