BLEVE: The Propane Cylinder
FEATURES
STRATEGY AND TACTICS
Two engine companies and two ladder companies respond to a report of a truck fire at a residential/business community. The officer of the first pumper on the scene sees smoke issuing from a large, enclosed lunch-wagon van. It’s parked alongside a curb, at a spot where a row of two-story frame dwellings end and a school playground begins.
The lunch wagon was open for business when the fire started. A hinged metal panel on the street side, three feet high and five feet wide, is held open over the serving area by two metal poles. Flames float out of the top of this opening.
“Pull up just past the truck,” the captain of the engine company tells the driver. “We’ll use the booster.”
Speaking into the radio handset, he gives a preliminary status report. “Engine 8 to Communications, we have a truck fire at King and Maple streets. No additional units required. Return the rest of the assignment.”
The officer then slides open the glass window behind him and briefs the three firefighters sitting in the jump seat. “Stretch the booster and take a hook and halligan tool for overhauling.”
“OK, Captain.”
The pumper stops in the middle of the road. The firefighters mask up and stretch the booster hose. The captain moves to the burning lunch truck, and checks the cab for victims. There aren’t any.
“Here comes the water!” one of the firefighters shouts as the line is bled of air.
The captain steps back from the truck, positions himself next to the firefighter holding the nozzle, and gives the command: “Hit it!” The stream penetrates the bowels of the truck through the open service area, and the flames are quickly driven back into the truck. The firefighters move in closer.
Whoosh! Boom!
The explosion is sudden, violent. A ball of fire blows back out of the truck’s side opening and the hinged panel slams shut. Flames reach out of the open cab door on the driver’s side.
“Stretch the 1 3/4 -inch preconnect!” the captain orders the firefighter behind the man who’s holding the booster line. The officer points to the firefighter holding the pike pole. “Open that hinge panel with the hook.”
When the booster and P/i-inch hoselines are ready for another attack on the fire, the firefighter with the hook crouches down below the flames, holding the hinged panel open. The hose streams blast away at the flames and, again, drive them back into the van.
Boom! A fireball and a blast of air erupt out of the truck. Two firefighters are knocked down. The hinged panel is blown off the truck into the air over the firefighters’ heads to the other side of the street.
Recovering quickly, the firefighters struggle to regain control of the open hoselines whipping around the street. The officer shouts back to the driver, “Take a hydrant?” He jumps up onto the back step and pulls off the nozzle with several folds of 2‘/2-inch hose and drops it into the street, then gets into the cab and calls for backup help on the radio. “Engine 8 to Communications, send the full assignment to King and Maple.”
The captain hops out of the cab and checks the exposure behind the burning lunch wagon. A fivefoot sidewalk separates the truck from the two-story frame dwellings. An old man and a child standing at windows are looking down at the firefighters in the street. A group of children have gathered behind the schoolyard fence, attracted by the fire and the explosion. The top of the truck is burning. A large orange-andwhite canvas umbrella affixed to the truck is engulfed in flames, and windswept pieces of charred canvas are blowing into the nearby dwelling.
“Captain, there’s got to be some kind of gas leaking inside that truck,” one of the firefighters reasons. The officer nods.
They both approach the burning truck, crawling below the flames that are shooting out of the open cab door. The captain is able to get a glimpse of the back of the lunch wagon. There, among piles of burning styrofoam coffee cups, a 20-pound propane cylinder is rolling around the floor, hissing and spewing flaming gas out of its valve opening.
Whoosh! Boom! A small amount of accumulated gas at the top of the truck explodes. One of the hose streams temporarily extinguishes the burning gas.
“Hold it! Back off with that hoseline—we have a propane cylinder in there!” the officer warns. He thinks to himself, “What am I supposed to do? What is the procedure for a burning propane cylinder?”
“Captain, propane is bad news. What should we do?”
Whoosh! Boom! There’s another small explosion inside the truck. Looking up at the dwelling, the captain sees the old man staring down at him, and remembers what he must do.
“Bring that 2 1/2-inch hoseline over here.”
He crouches at the open cab door and turns to the firefighter who’s ready and waiting with the hoseline, the nozzle closed. “When I crawl in there, keep the fog stream directed at the top of the cylinder while I try to shut it off.”‘
The firefighter nods. There is a moment of hesitation. Then, adjusting his gloves, the captain crawls into the truck on his elbows and stomach, below the reach of the flames. He approaches the burning propane cylinder under protection of the fog stream. He grabs the collar of the moving cylinder and steadies it with one hand. With the other he takes the control wheel handle and slowly turns the valve. He lowers his head, staring down at the metal deck of the truck just inches from his face. His entire body shakes as he twists the valve clockwise….
Siam!
He freezes.
“Captain, it’s OK—a burning tire just blew!” the firefighter with the nozzle shouts over the rumble of the spray stream striking the metal walls of the truck, over the hiss of the propane cylinder.
The cylinder valve finally meets resistance. It closes tightly, and the hissing stops. “That’s it, Captain, you got it,” the firefighter says.
Crawling back out of the truck beneath the fog stream, soaking wet, the officer takes off his helmet, walks over to the pumper, and sits down.
Sirens are sounding nearby — the other companies are pulling into the block. Someone taps Engine 8’s captain on the shoulder. He turns around. It’s the battalion chief.
“Say, Captain, what’s all this? Three hoselines stretched, calling for the full assignment—don’t you think you’re overreacting?”
“Chief,” replies the captain, “you should have been here a couple of minutes ago.”
QUESTION 1: When is the danger from a propane cylinder BLEVE (boiling-liquid, expanding-vapor explosion) greatest?
A. When the relief valve is operating and burning.
B. When a flame impinges on the cylinder bottom, which is the liquid portion of the container.
C. When a flame impinges on the cylinder top, which is the vapor portion of the container.
D. When there is a gas leak and no fire.
QUESTION 2: What’s the correct procedure when directing a hose stream at a propane cylinder that’s exposed to a nearby fire and whose relief valve is burning?
A. Extinguish the exposing fire first.
B. Cool the propane cylinder near the top first.
C. Cool the propane cylinder near the bottom first.
D. Use no water on the fire.
ANSWER TO QUESTION 1: The correct answer is C. The danger of a propane cylinder BLEVE is greatest when flame impinges on the top of the cylinder, which is the vapor space.
ANSWER TO QUESTION 2: The correct answer is B. Firefighters should first direct a hose stream to cool the top of a propane cylinder.
Over the past two decades, there has been a dramatic increase in the use of small, portable cylinders of liquefied petroleum gases at home and at the workplace. These 20-pound cylinders—generally propane or butane—are used for cooking, home repair torches, lighting, and heating, and are often found inside garages, house cellars, auto repair shops, plumbing warehouses, and housing booths at convention centers and indoor festivals.
There also has been a dramatic increase in the number of firefighters killed and injured by explosions of small, portable propane cylinders.
Firefighters advancing initial attack hoselines on routine fires in trucks, house fires, garage fires, and trash fires have unknowingly stepped right into propane cylinder explosions. The deadly byproducts of such explosions—fireballs, cylinder projectiles, flying shrapnel, and shock waves—can seriously burn, maim, or kill a firefighter, blast him out of a window, or effect the collapse of a building in which he’s standing.
There’s been a dramatic rise in the number of firefighter deaths and injuries due to 20-pound propane cylinder BLEVEs.
Before firefighters are trained in tactics to control a fire near a portable propane cylinder, they should be aware of the reactions of a propane cylinder under fire and of the deadly by-products of BLEVEs. Knowledge of these reactions and explosive dangers is absolutely necessary for the fire officer in his risk assessment of fireground operations when propane cylinders are involved in routine fires.
The fireball
A BLEVE is not a fireball. A fireball is but one result of a BLEVE. It’s caused by the instant vaporization and ignition of the liquid propane released to the atmosphere when the cylinder blows apart. Propane liquid expands 270 times in volume as it converts from liquid to vapor. One cubic foot of propane can expand into 270 cubic feet of vapor, with sudden explosive results.
The size of the fireball created by a propane cylinder BLEVE depends on the amount of liquid stored in the cylinder. These containers aren’t completely filled with liquid; room is allowed for expansion of the liquid due to temperature variations. Before use, the volume inside these common 20-pound cylinders is about 80% propane liquid and 20% propane gas. Therefore, a so-called 20pound cylinder will contain about 17 pounds of liquid propane, or approximately 4 gallons of liquid propane weighing approximately 4.23 pounds per gallon. One gallon of propane liquid, if completely vaporized during a BLEVE, could create a fireball that’s 36 cubic feet in volume; that’s approximately three to four feet in diameter. A “full” tank—four gallons—of liquid propane completely vaporized during a BLEVE could create a fireball of 144 cubic feet, approximately five to six feet in diameter. Of course, fireballs don’t travel outward in neat, mathematical packages; the distance covered could in reality be more than six feet.
Most firefighters have seen photos of large storage tank explosions that produce gigantic fireballs several hundred feet in diameter. They’re aware that death from burns to firefighters have occurred within a radius of 250 feet from large storage containers of liquefied petroleum gases.
Of course, the fireball created by a small propane cylinder explosion won’t be as large. Firefighters using the reach of a 30to 50-foot hose stream on a 20-pound propane cylinder will be safely positioned out of the range of the fireball which may occur in the vicinity of the exploding vessel. However, the firefighters are in great danger from rocketing cylinder parts, a trail of burning liquid propane, and the air blast of the explosion. These, even more so than the fireball, are factors that impact risk assessment.
Projectiles and shrapnel
Firefighters directing a hose stream could be decapitated or crushed to death if struck by a chunk of steel cylinder rocketing through the air at sonic speed. They could also be doused with burning liquid propane that’s spewed out in the wake of the rocketing cylinder.
It’s impossible to determine exactly how a propane cylinder will break apart during a BLEVE. All we can safely say is that it will fail at its weakest point during a fire. The weakest point will be determined by the cylinder’s exposure to fire —the heat and pressure weakens the molecular structure of the metal casing—or by any defects or damage to the container from handling.
In some fires, the control valve mechanism blows off and becomes a deadly piece of shrapnel, shooting outward far beyond the area of the fireball. At other fires, the tank splits at the seam and separates into two parts. If the tank is full of propane at the time of explosion, the rocketing cylinder will leave a trail of burning liquid and vaporized propane.
The distance a piece of steel can be blown away from the explosion depends, in part, on the size of the container and the amount of liquid petroleum gases stored inside. BLEVEs of large tanks have blown metal pieces up to ½-mile away from the explosion. Firefighters who were 800 feet away from a BLEVE have been killed from rocketing tank parts. Obviously, a small cylinder will not cause flying shrapnel to travel as far as a large propane tank will; however, firefighters directing a 30or 50-foot hose stream on an exploding small cylinder are within range of rocketing projectiles and could be killed or seriously injured.
The distance covered by metal shrapnel from an exploding propane cylinder is also dependent on which section of the cylinder fails. If the cylinder remains in one piece and only the control mechanism and valve blows off, it will travel farther than if the tank splits into two large sections. A small piece of rocketing cylinder such as a control handle mechanism is not unlike a bullet or cannonball. If, on the other hand, the propane cylinder splits apart or tears open at the seam, the larger chunks of metal may not travel as far away from the explosion. However, this type of cylinder rupture creates a larger fireball.
Photo by Paul Dansbach.
Test explosions and postfire analysis have revealed that, when propane cylinders explode, the main section of the cylinder will rocket in a direction opposite the gas release or failure area of the cylinder. For example, if the bottom of a cylinder laying on its side “BLEVEs,” the largest section of the container will travel in a direction away from the bottom of the cylinder. The area near the ruptured bottom of the tank will be the direction of the fireball and the direction of the greatest shock wave or blast.
Explosion shock waves
The definition of an explosion, according to the NFPA’s Handbook of Fire Protection (16th edition), is a “rapid release of highpressure gas into the environment.”
This rapid release of high-pressure gas results in shock waves. These shock waves are actually blasts of air which transmit in outward directions the high pressures created by the explosion. They may vary from supersonic shock waves to a mild wind. The speed and force of the shock waves depend on how much “high pressure” is created by the explosion.
When an explosion occurs inside a building, the shock waves transmitted are confined by walls, floors, and partitions. These confined shock waves, if they don’t collapse the building, can become deadly, concentrated blasts of air. Firefighters standing near openings during an explosion can be lifted off their feet and blown into the air or out of a building. They’ve been blown off open floors of buildings under construction; blown into elevator shafts —together with the hoistway doors; blown through glass windows by the shock waves of explosions.
The deadly effects of shock waves from propane cylinder explosions can be extensive —far more extensive than the effects of fireballs and rocketing projectiles. When the shock waves create internal pressures that exceed the strength of the walls, roof, or floors of a building, massive total collapse occurs. On July 21, 1987 in Brooklyn, N.Y., one 20-pound propane cylinder exploded in the cellar of a plumbing supply company. The explosion and ensuing shock wave collapsed three twostory buildings, killing four people. Five years ago in Buffalo, N.Y., the shock waves of an explosion caused by a leaking propane cylinder collapsed a 200by 100foot brick building, killing five firefighters.
When a propane cylinder inside a building is heated by fire and explodes, there are actually two explosions (and two waves of shock). The first explosion is physical, which is the BLEVE or rupture of the propane cylinder; and the second is chemical, which is the fireball or rapid ignition of the vaporized propane. The shock waves created by the physical explosion or cylinder rupture will travel outward from the side of the cylinder where the rupture occurs. The shock waves created by the second explosion or fireball may be more severe and extensive: these highpressure shock waves travel in all directions.
The shock waves of the chemical explosion or fireball will be the most destructive when they occur inside a building.
The explosion of a fireball and subsequent collapse of a building will take place as follows:
- The vaporized propane mixes with air.
- The gas/air mixture is ignited.
- Heat is absorbed by the surrounding air in the room.
- The confined, heated air expands to double its original volume for every 459°F (237°C) it’s heated.
- The heated air not free to expand (that is to say, heated air that’s confined by the walls of the room) creates an increase in pressure.
- The rapid increase in pressure will create shock waves that will break windows, collapse interior partitions, and blow out the walls and floors of the entire building, if strong enough.
Vapor space and spot fire
A 20-pound propane cylinder contains propane liquid and propane vapor. The liquid portion is the bottom area; the vapor portion is the upper part. Most BLEVE failure of cylinders originate in the metal of the vapor space.
During a fire it’s extremely difficult to heat a cylinder to its explosion point when flame only contacts the liquid portion, or bottom. The most dangerous fire is one in which flame impinges on the upper portion of the cylinder or vapor space. The heat from the flame increases the temperature inside the container; the increased temperature causes the propane vapor to expand and weakens the metal shell of the cylinder; the increase of pressure inside the cylinder opens the pressure relief device; and if a continued rise in pressure occurs, the cylinder will “BLEVE”.
The very dangerous condition of upper cylinder impingement is further aggravated by a “spotfire,” in which a propane cylinder is secured to a truck, barbecue, or side of a house, and flames issuing from a burning cylinder valve, relief valve, or tubing are deflected off a nearby object and back onto the vapor space of the cylinder. Barbecue stoves, truck bodies, and brick walls can deflect flames back onto the top of the cylinder.
Propane cylinder fire tactics
When a large propane cylinder is burning around the cylinder valve, the correct firefighting tactics are: 1) cool the top vapor space of the container; 2) shut off the gas by the control valve if possible; 3) if the flow of burning gas can’t be shut off, allow the propane cylinder to burn itself out and use the hose stream to protect exposures.
When a small, 20-pound cylinder is burning at the valve it’s often possible to quickly shut off the flow of gas without cooling it. A hose stream used to cool a burning 20-pound cylinder may accidentally extinguish the flame, and if the gas reignites before the control valve can be shut off, a more serious condition could be created, injuring the firefighters attempting to shut off the valve.
The most common emergency involving a 20-pound propane cylinder leak is fire around the control valve or the tubing leading from the cylinder control valve outlet.
Firefighters encountering this problem should first attempt to shut off the control valve handle. If the control valve handle is melted or missing, or if the valve is leaking gas around the packing nut below the valve handle, a vise grip or pliers may be used to turn the valve stem or tighten the packing nut. If metal tubing leading from the cylinder is leaking and the valve handle and stem can’t be manipulated to stop the leak, crimping or crushing the tube may stop the leak. Use a vise grip or pliers to “doublecrimp” or bend the tubing. A “Z”type crimp, similar to the one used on a hoseline to temporarily stop the flow of water when it’s burst, is effective.
Fire officers supervising the hose stream at a propane cylinder fire must know safety principles of hose stream direction.
A fog stream at 30-degree fog pattern will give the greatest cooling effect and provide the greatest safety reach. The fog stream should always be directed at the top of the container or vapor space to provide maximum cooling effect.
The fire officer must realize that a stream of water from a l3/4-inch hoseline that’s misdirected on a burning cylinder could extinguish the flame, and escaping gas may create an even greater danger from reignition —fireball, shock waves, and if indoors, collapse.
Safety demands that correct procedures be followed when shutting off the cylinder valve. The fog stream is adjusted from 30-degree fog stream to wide-angle fog stream (this decreases the likelihood of extinguishment). The fog stream is positioned between the shut-off valve and the burning outlet. Two fog streams angled in overlapping fashion may be used for maximum firefighter protection. Never extinguish a propane gas fire unless the fuel can he shut off at the valve immediately.
A recent propane cylinder incident produced this course of events: After extinguishing a house fire, a loud hissing noise was heard and a scorched 20pound propane cylinder discovered among a pile of burned rubble. Its relief valve was discharging propane gas. A fire officer quickly picked up the discharging cylinder and threw it out of a window into a backyard. It safely discharged its contents until the tank was cooled and the relief valve reset. Afterwards, the officer agreed that such rough handling of the propane cylinder could have resulted in dislodging the control valve or denting the tank, creating a larger, unstoppable leak. However, he concluded that this was preferable to the continued gas accumulation and potential explosion inside the structure.
A room can explode when less than 25 percent of the enclosure contains flammable gas-air mixture. It’s erroneous—and dangerous—to assume that a gas-air mixture needs to fill an entire room before an explosion can occur. Therefore, prompt removal of the leaking cylinder is imperative.
In some communities, owners of high-rise apartment houses prohibit tenants from keeping propane-fired cooking stoves on open-air balconies. Some tenants, naturally, try to beat the regulation by stowing the barbecue inside the apartment and sneaking it out onto the balcony for brief periods of use. Keeping the cylinder inside the apartment is not too clever, of course, when it comes to fire.
If, after a fire in such a place, a scorched cylinder is discovered with the relief valve discharging gas, it should be quickly carried out to the balcony and cooled with a 30-degree fog stream. The windows and doors from the outdoor balcony to the apartment should be closed to prevent wind from blowing gas back into the apartment. If the relief valve is a resetting pressure device, it will close when the cylinder is cooled. If the relief valve is not resetting, the cylinder valve should be opened to speed up the gas discharge and a hose fog stream played on the leaking gas to dissipate it into the open air.
Moving a propane cylinder requires the following safety precautions whenever possible:
- Firefighters should wear full protective clothing on all parts of their bodies (helmet, turnout coat, gloves, boots or lumber pants, no-
- mex hood, and face mask of SCBA donned).
- The control valve of the cylinder should first be shut off.
- If there is a nearby fire exposing the cylinder, the firefighter who’s moving the cylinder should be under cover of a hose stream, or else a hose stream should be charged and ready for use.
- The cylinder should be approached from the upwind side.
- The firefighter should carry the cylinder with the relief valve pointed away from the body; in that way if the relief valve suddenly operated, the firefighter would not be drenched with propane gas or burned by a fireball.
- The wind should be at the firefighter’s back during the entire movement of the cylinder.
- The 20-pound propane cylinder should only be moved in an upright position. If it’s laying on its side, it should be uprighted first, before moving. The relief valve is designed to operate when the vapor space is at the top of the cylinder. If the propane cylinder were laying on its side and the relief valve suddenly activated, liquid propane could be discharged from the opening.
TH ires involving burning or leaking 20-pound portable propane cylinders can be routine—or they can produce deadly explosions. If improper firefighting tactics are used in the handling of these cylinders, boiling-liquid, expanding-vapor explosion could occur, a fireball could ignite around the cylinder, the metal tank could rocket 50 to 100 feet through the area at sonic speeds, a structural collapse could occur— any one of which could kill a bystander or firefighter.
The margin for error in firefighting tactics at a propane cylinder fire or leak is very small; mistakes can quickly turn into fatalities. Fire officers must be thoroughly knowledgeable in this area to make rapid risk assessments and initiate proper strategy and tactics; firefighters must have the procedural know-how to carry them out without hesitation. Safety demands it.
