The Connecticut Fire Academy Skill Sheet 22. Recruit Firefighter Program Fire Suppression / Propane Tank Practical Skill Training Instructor Reference Materials Fire Engineering.com Propane Gas Barbecue Grill Fire: Expect a BLEVE by Scott Joeger On December 3, 2015 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 of 8 Revision: 031917 The Connecticut Fire Academy Skill Sheet 22. Recruit Firefighter Program Fire Suppression / Propane Tank Practical Skill Training Instructor Reference Materials 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). (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.) 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. 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. (2) The top of a 20-pound propane tank showing the pressure-relief valve, the cylinder valve hand Intense flames were concentrated inside the cabinet up wheel, and the gas point of connection. toward the top of the tank at the vapor space. (Photos 2-5 by author.) 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. 2 of 8 Revision: 031917 The Connecticut Fire Academy Skill Sheet 22. Recruit Firefighter Program Fire Suppression / Propane Tank Practical Skill Training Instructor Reference Materials 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. 3) This propane gas barbecue grill has the (4) This propane gas barbecue grill does propane tank fully enclosed in a cabinet. 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.