BLEVE- Boiling Liquid Expanding Vapor Explosion April 29, 2007
Posted by gaussling in Chemical Industry, Chemistry, Chemistry Blogs, Current Events.trackback
There is kind of fire behaviour called a BLEVE- Boiling Liquid Expanding Vapor Explosion. A BLEVE is what happens, for instance, when a closed container of flammable liquid is exposed to strong heating. It can be caused by an external source, like a pool of burning liquid around the container, or it can result from a runaway reaction within a drum, cylinder, or tank. The internal pressure builds up more rapidly than it can be vented and the containment fails, often explosively.
Given that there is probably an ignition source already present, the rapidly expanding cloud of hot vapor and aerosol ignites. At minimum, the ignition will lead to a deflagration, or if conditions are right, a detonation of a fuel/air mix could happen over a relatively large space.
These things often begin with some kind of tanker accident resulting in a discharge and ignition of flammable liquid. As responders arrive they find a burning pool underneath the tanker. Naturally, firemen and bystanders try to help those who may be hurt. As the minutes tick away and the fire becomes more aggressive and the tank gets hotter, the firefighters get their equipment in place and attempt to cool the tanker and suppress the fire. Suddenly it explodes violently yielding a large fireball and heat pulse. It is at this point that the surviving bystanders and responders see the error of their ways.
Containers of flammable liquids rarely explode in a symmetric fashion so the container or its fragments are likely to be sent flying at high velocity, possibly spewing flammable material as it moves. Even a relatively small volume of flammable liquid dispersed explosively can fill a large surrounding space with a fireball.
All chemical plants have their protocols for emergency response. It is important for those in charge to recognize an incipient BLEVE and respond accordingly. But even academic chemists should familiarize themselves with the phenomenon. A fire in the lab engulfing closed containers of flammable solvents is extremely dangerous and very quickly firefighting may become your last earthly act, especially without personal protective equipment. It is easy to under estimate the violence of these things.
Every lab person needs to look inward and decide what their personal limit is for dropping the fire extinguisher and running for the exit. In my sophomore organic labs, the seed I planted in the students mind was this: The main purpose of a fire extinguisher was to fight your way to an exit.
The most meaningful training I’ve ever recieved since I left grad school was the fire training I took at 3M. The guy from the local fire department lit a 8′ x 8′ pan of heptane floating on water, gave me a fire extinguisher and a unforgettable half-smile that said “Let’s see what you can do”. What I remember the most is the heat of the flames as I got closer, especially on the face.
About the time that I got laid off, there was a trend towards “virtual” fire fighting using some kind of video display,… as the real fires were “too expensive”. Insane. The last couple of paragraphs you wrote are right on. If I were king, I’d make fire training a requirement for a chemistry degree (Chem Eng too).
Water pooled in a burning tank of hydrocarbon from fire hoses or wet foam is the classic do-gooder BLEVE. Hydrostatic head prevents boiling as the medium continues to heat, then WHAMMO! Gasoline in a tanker might barely pull that off. Tankage rupture and flash decompression is a better bet in the latter case.
Thermite demos can be BLEVEs. A terra cotta flower pot with filter paper covering its bottom hole is suspended over a tray of deep sand to catch dripping molten iron. If somebody gets clever and uses wet sand… WHAMMO!
[...] however, 4th of July demonstrations never celebrate lab explosions or hood fires. A good BLEVE is a real crowd pleaser and a sight to behold. Professional pyros choose the more cosmetic [...]
it was nice of u to share d knowledge and info.
thank u.
[...] is less than routine, however, is the issue of BLEVE’s. I have written on this phenomenon previously. Fire suppression is one thing, but BLEVE’s - Boiling Liquid Expanding Vapor Explosions- [...]