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Sunday, September 22 2019 @ 08:38 am EDT

LPG Tanker Truck Fire in Panama City - Detailed Description of Events (Chronological Order)

Safety & SecurityBy DON WINNER for - Late yesterday afternoon I had a long conversation with a person in the United States who is intimately familiar with the construction, use, and operation of the LPG tanker trucks of the type involved in the fire in the banking district of Panama City on Tuesday. Later this morning I will be meeting with the officers who work in the fire department's Office of Safety and Security who are responsible for investigating incidents such as this and preparing an official incident report. At this point I think I have a pretty clear understanding of how this incident occurred and progressed. I will run through my version of the scenario quickly for you all, then I'm off to meet with the fire department to deliver the details to them. This is how it went down. (more) (Note - I'm publishing the text now and working to add the photos)
  • Delivery Truck Arrives: The Tropigas 3,000 gallon capacity LPG tanker arrived at the Americas building in the banking district to make a delivery. There is a restaurant in the ground floor of this building, with apartments in the upper floors. The restaurant has a 500 gallon tank behind the building which they use for the kitchen in the restaurant. This supply tank for the restaurant has probably been refilled safely hundreds of times.

  • Working Alone: Normally the Tropigas delivery driver works alone. His first task would be to position the vehicle to make the delivery, which he did by backing the truck along side of the building to get as close as possible to the restaurant's 500 gallon tank located behind the building. Once the truck was positioned, he would exit the cab of the truck and leave the engine running.

  • Start The Pump: There is a fuel pump located on the driver's side of the truck, between the front and rear wheels, below the tank. There is a kind of transmission which connects the pump to the truck's engine. The pump gets the energy to pump the fuel from the truck's motor, and the driver would have to engage that transmission to arm the pump to make the delivery. The liquid LPG fuel exits the main tank of the truck at this point and flows through the pump towards the back of the truck where the delivery hose and fuel meter is located.

  • The Driver Never Made It That Far: I have solid photographic evidence indicating the LPG tank truck driver never made it to the back of the truck. The panel to access the delivery hose and meter was closed when the fire started. I believe this accident started when the driver actuated the pump.

  • "A Large, 2" Hole: According to my expert, in order for a very large amount of fuel to spill like that you would need a relatively large hole to open up somehow, and he described something "about 2" in diameter." He said that if you could just open the fuel delivery hose up and spray it into the air, you wouldn't get much of a liquid spill but more of a spray as the liquid turns to gas as soon as the pressure is released. LPG does not want to be in a liquid form at 87 degrees Fahrenheit and one (ambient) atmospheric pressure. It wants to be a gas so it evaporates very quickly and one of the byproducts of that rapid evaporation is cold - which explains the formation of ice on some of the parts of the truck (more later.)

  • Probable Valve Failure At The Pump: I think the original serious spill occurred when the Tropigas LPG tank truck driver actuated the pump mechanism. Now, I have to assume at this point that the problem or failure was accidental or mechanical in nature. I don't know enough about how that particular model of pumping mechanism and values are operated to even speculate on the possibility of operator error. Anyway, no matter how it happened (mechanical failure or operator error) at this point a very large volume of LPG was released from the bottom of the truck near the pumping mechanism. There is still no fire yet at this point.

  • Liquid Propane Running Down The Street: First of all, propane gas is heavier than air. If there is a massive leak from a truck like this, and fuel or vapors would have run downhill just like water. Lacking a strong wind, any heavy concentration of fumes would also run downhill, following the natural contours of the ground, but since it's now in gas form rather than water, it's floating just above the ground. So, the LPG leaves the tank in a liquid state but it wants to be a gas once it's out of the pressure tank, so in fact it would not have remained as a liquid for very long. In reality what went "running" down the street was probably not a liquid, but the strong concentration of LPG gas in a dense cloud form, floating just above the surface of the ground. Since it's heavier than air, it "ran" downhill, displacing the air as it goes.

  • Testimony and Video Evidence: Incredibly, the tank truck driver survived this accident. He has already been interviewed and has made his statements to investigators. In addition there is a video tape captured by a security camera that happened to be pointing in the direction of the LPG tanker truck with the initial leak and spill occurred. This video was shown on Channel 13 Telemetro news as part of their coverage of this accident. The news reporter said "and you can see the white smoke coming from the area of the truck" but in fact that's the LPG fuel vapors, quickly evaporating as the fuel is dumped onto the ground thanks to the problem with the tanker truck (either mechanical failure or operator error.)

  • Vapor Finds An Ignition Source: It could have been anything - a spark, a running car - and in reality it doesn't really matter all that much. But somewhere this dense cloud of LPG gas found an ignition source and that was the first explosion. This explains why all of the cars that were parked on the street had their hoods blown "up" from below. The heavier than air and very densely concentrated LPG gas cloud had run down underneath all of these vehicles. When it went off, there was a very loud explosion as all of that fuel burned simultaneously. The fire "followed' the gas all the way back to the LPG tanker truck and the original source of the fuel. The front end of the tanker truck caught on fire and started burning. Several of the vehicles that were parked on the street also caught fire. The garbage that was in bags in front of the building also caught fire as well. Practically any flammable material that had been soaked in these LPG has fumes caught fire.

  • LPG Tanker Truck On Fire: This is the nightmare scenario. Now there is a 3,000 gallon LPG tanker truck burning. The tanker truck itself is still almost fully loaded. At this point the original valve that failed (or was accidentally left open) was probably still open, so the burning truck has a steady source of new fuel and it's burning hot. However the pressure is not building in the truck because the valve is still open, allowing the fuel to exit the truck and effectively releasing the pressure in the main tank. So right now it's a truck fire with a whole lot of fuel.

  • The First Safety Feature Actuates: The very smart people who design and build these trucks planned for the eventuality of this scenario. "What happens if the value fails and the truck catches fire?" They built in what's called a "fusible link" specifically between the main body of the LPG tank and the area of the pump and valves. Once the fire started and the truck started burning, the heat melted this "fusible link" by design which closed the connection to the values and shuts down the flow of fuel. This acted to contain the remaining fuel in the tank and to remove the original source of fuel from the fire. That's good, but it causes an additional problem.

  • Fuel, Heat, Fire, and Pressure: The truck is still on fire. After the fusible link activated and shut down the flow of fuel, the cab of the truck is still burning hotly. The pressure in the tank increases to a point where the integrity of the tank itself might be compromised. That's when the second safety device built into these trucks actuated. There are several pressure release valves built into different parts of the truck. These are designed to allow for the rapid release of pressure in a situation such as this. Once the pressure in the truck reached a predesignated level of pressure, the pressure release valve actuated and this is what caused the 150 foot tall column of flame that shot straight up into the air. That column of flame continued for a long time because the valve remained open to literally blow off the pressure until the pressure in the main tank returned to a safe level. Again, remember that the priority here is to prevent an even more catastrophic explosion. If that main tank had actually exploded then every building in a very large radius would have been blown down and hundreds of people would have potentially been killed. This safety feature undoubtedly saved many lives because it worked as designed. Thank God.

  • Pressure In Main Tank Drops: Once the pressure in the main tank dropped back down, the pressure release valve closed and the flow of gas stopped. The fire department was in the process of responding to this fire, and one of the first things they did was to extinguish the front end and body of the burning LPG tanker truck. By putting out this fire they eliminated the primary source of heat that was increasing the pressure in the main tank. As the continued to work to put out the fire burning in the apartment building above, the kept a couple of hoses on the tanker truck to keep it cool. This action probably prevented the pressure release valve from actuating again later. So, by this point the LPG gas in the truck has been contained, thanks to the fusible link and the pressure release valve.

Pressure Release Valve Has Actuated: Now, you see this photo in a different light. You can see the fire burning below the truck, from where the truck itself was on fire. The heat and pressure has increased and the pressure release valve has actuated (opened) to allow the pressure to blow off. If this safety feature had failed and the pressure in the tank had been allowed to build until it exploded, this would have eventually ended up in a Boiling Liquid Expanding Vapor Explosion (BLEVE) which would have literally leveled the banking district and killed dozens or hundreds of people. This Youtube video accurately describes what would have happened if the fire department had not arrived to extinguish the truck fire and to keep the tank cool.

That Was A 1,000 Gallon Tank: Also, you should recognize that the tank in the video was about a 1,000 or 1,500 gallon tank while the tank on the truck was 3,000 gallons. Bigger tank, bigger boom.

Back Panel Closed: As you can see in this image, the back panel of the truck is still closed as the fire burns. Normally, if the driver was in process of delivering fuel when the fire started, you wold expect this back panel to be opened. I'm relatively sure he never made it that far.

Back Panel Closed: And this is one of the first images I was able to take of the back of the truck. Notice that the door on the back which is used to access the delivery hose and pumping controls is closed at this point. That same panel is also closed in the photo on the cover of the El Siglo newspaper.

Back Panel Now Opened: I took this photo of the back of the truck when I accompanied the Chief of the fire department's Office of Safety and Inspection, at his request, to take some incident photos. At this point a couple of representatives from Tropigas had been back here before us, and apparently they were the ones who opened the back panel. Now that I've had time to study these photos a couple of things leap out at me...

Current Pressure in LPG Tank: This is a closeup photo of the pressure gauge on the tank. Above this gauge there is a sign which reads "Manometro" which means pressure gauge. I can't see or read the outside scale but the inside scale is at "10" - these kinds of gauges tend to be "happy" when the needle is pointing straight up or in the middle. Anyway, I'm sure an expert can tell me what this gauge reads with this image. Please make a comment to this article below. Thanks.

Current Temperature of LPG Tank: At the time this photo was taken the inside of the tank was reading about 38 degrees Celsius or about 100 degrees Fahrenheit. This tank is very hot and they are normally only rated to 50 degrees C.

The Real Heat Never Got Here: Apparently the real heat from the main fire never reached this back part of the truck. Notice that there are several items made out of rubber and plastic, like the traffic cone for instance, that would have burned or melted if the fire had reached this area. What's more there is ice formed on some strange parts of this truck in the back, indicating that large amounts of expanding vapor had been through here, causing the creation of ice as it evaporated. But, the ice is formed on some parts of the truck that are not pipes and don't carry fuel, such as the support rod below the hose reel, so the guess is that a lot of the expanding fuel came through this area and then the ice was protected from the heat of the fire by the closed panel and compartment.

Ran Out Of Time: Now I have to run over to the fire department to deliver some photos and videos, and to explain all of this to them. I'll add more later when I have more time. The bottom line is - the safety features of this vehicle worked as designed to prevent a much larger catastrophe. We dodged a bullet here...

Copyright 2009 by Don Winner for Go ahead and use whatever you like as long as you credit the source. Salud.

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