BLEVE Explanation

[SkipJack270]

This goes back to another thread, and a question I had for y'all.
PLEASE NOTE: I AM YOUNG AND INEXPERIENCED. I AM TRYING TO BECOME BETTER AND MORE INFORMED, THEREFORE I AM SIMPLY LOOKING FOR INFORMATION. PLEASE DON'T JUMP ON MY STUFF JUST BECAUSE I AM ASKING A QUESTION. THANK YOU.
That being said, here is my question: I now understand the concept of relief valves and dump valves, curtesy of some kind jakes from the other thread. However, I am now confused as to why, if tanks have relief and dump valves, BLEVE's are possible. I understand malfunctions and whatnot, but is that the sole cause of all BLEVE's? Or is there something I am missing? Thank you.
(P.S. Sorry about yelling before, but there seems to be a trend on FH that when some older and undoubtably wiser firefighter considers one of us younger guys question stupid, they will immediatly melt that poor persons computer moniter. I just wanted to make clear that I understand I am a FNG, and that I know ***** compared to most of you.)

[Co11FireGal]

I'm not always the best at explaining things, but I'll give it a try...

A BLEVE (Boiling Liquid Expanding Vapor Explosion) happens when a tank containing a liquid above its boiling point, at regular atmospheric pressure, fails. It can happen for several different reasons, but the most common is the internal pressure in the tank increasing due to it being heated up by fire, and the flames weakening the tank to a point that it just blows apart. At first, when a tank is involved in a fire, the liquid inside the tank heats up and the metal tank is allowed to stay cool. As the liquid heats, it gives off vapors, and the pressure inside the tank increases and that is when you'll get the fuel venting off by way of the relief valve. When the pressure returns to a safe level, the relief valve will stop venting, and the process starts again. Over time, the liquid level of the tank is dropping, and more and more of the tank is heating up from the flames impinging on it, and as it heats the tank is weakened and eventually the pressure builds until it is too much for the weakened tank and it blows apart. When it does, the sudden decompression causes a blast and the liquid inside the tank is above it's atmospheric boiling point so it boils off, turning into vapor, and all that vapor and whatever liquid droplets are left are dispersed and ignited, making your nice big fire ball.

The reason why it's usually not safe to make an attack on a fire with manned lines is because you don't know when or if the tank will fail. You don't know if that relief valve was already venting before you got there, you don't know the level of liquid in that tank or if it is keeping the metal cool enough to not be weakened...you don't know if that tank was already weak for some reason, like because of mechanical damage or corrosion. Also, chances are, a first arriving engine will not be able to supply enough water to keep that tank cool enough. It takes about 500 GPM per point of flame impingement to do the job...

[Co11FireGal]

BTW, there is a great diagram of how a BLEVE works in this book...you can get the book for about $45, maybe less if you can find it on E-Bay or Amazon or someplace like that. It is operational level material, and it is presented in a very clear and concise manner.

[SkipJack270]

Awesome. Thank you for the explanation, and book reference. It's my personal hope that I can learn from the FF's who have been there beofre me, and through listening and asking questions, I can both become better informed, and at the same time become a better firefighter candidate. Thanks again.

[DeputyChiefGonzo]

Co11firgal's explanantion summed it up in a nutshell.

the pnemonic BLEVE also has another meaning..
Blast that Levels Everything Very Effectively!

fyi: a 20 pound propane tank, commonly found on just about every gas grill ever made, has enough "bleve power" to level the typical single family home! Scary thought when you realize that some morons bring the tank into the house, despite the warning labels written all over it!

[GeorgeWendtCFI]

Damn girl, you did good.

Just one tiny addition. You DO NOT need a flammable liquid to have a BLEVE. I have seen a video of a test where they put 10 gallons of water into a horizontal 55 gallon drum and set up a fire to impinge on the top of the drum. After about 10 minutes, it BLEVE'd. Rocketed quite a distance. Only thing was, of course, no fire.

[FWDbuff]

the pnemonic BLEVE also has another meaning..

Also......"Big Loud Explosion Very Exciting."

[jaybird210]

One other little side note. Jack, you asked about dump and relief valves and in the presence of these, how is a catastrophic tank failure possible. The answer is, when the amount of vapor created (be it steam from water or explosive vapor from a flammable liquid) becomes greater than what the relief valve can vent, and over-pressurizes the container to the point of failure.

Any sealed container can BLEVE, even if it is "empty." We just have to heat it to the point that the air, water, LP ga, etc., expands until the container fails.

[nmfire]

Big Leveling Explosion Vaporizes Everything

Relief valves can only vent so fast. When a tank fails due to overpressure, it's simply a matter of the pressure going up a lot faster than any relief valve is going to blow it off. This is of course assuming the tank even has a relief valve.

[E229Lt]

it's simply a matter of the pressure going up a lot faster than any relief valve is going to blow it off

Anyone who has heard the, unmistakable high pitched, whistle that precedes a tank failure will tell you it's time to abort operations and take cover.

[nmfire]

Command to dispatch, please advise all units to (#*&$# run for it.

[DeputyMarshal]

Originally posted by GeorgeWendtCFI
You DO NOT need a flammable liquid to have a BLEVE....Only thing was, of course, no fire.

That's why it's not a BLEVE.

(Forgive me for picking nits, GW, but this one is on my pet peeves list from my instructing days. Only a true BLEVE is a BLEVE. Something that just looks like a BLEVE isn't.)

For a true BLEVE, you have to have a flammable/combustible material. No ifs, ands, or buts. As you said, however, even non-combustible materials -- like water in your classic example -- can create some violent tank failures that meet the other, unofficial definition of BLEVE: Blast Leveling Everything Very Effectively.

With non-combustibles all you get is the BLEV without the E(xplosion). You do get some pretty impressive catastrophic container failures but they aren't BLEVEs.

[SkipJack270]

The high pitch whistle being the classic sign of....what, exactly?

[F52Westside]

DeputyMarshal- Only a true BLEVE is a BLEVE. Something that just looks like a BLEVE isn't.)

I think George is correct there is nothing in "B.L.E.V.E." that mentions Flammable or Combustible. water can be a "Boiling Liquid" produce "Vapors" and "Explodes". I know BLEVE is usually attributed to flammable and combustible liquids, but I don't remember that being a must in the definition.

BLEVE, pronounced blevy, is an acronym for Boiling Liquid Expanding Vapor Explosion. This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous. When the liquid is water, the explosion is usually called a steam explosion.

From Wikipedia

[Skwerl530]

The whistle is typically the relief valve opening. Also keep in mind that as a metal container is exposed to heat it is weakened. If the metal is on a container the amount of pressure it can hold is decreased. If the pressure in the container passes that magic point then it will BLEVE. It's kind of like the gusset plates in trusses or metal trussed roofs. Expose them to extreme heat and bad stuff happens.

[GeorgeWendtCFI]

Originally posted by DeputyMarshal

That's why it's not a BLEVE.

(Forgive me for picking nits, GW, but this one is on my pet peeves list from my instructing days. Only a true BLEVE is a BLEVE. Something that just looks like a BLEVE isn't.)

For a true BLEVE, you have to have a flammable/combustible material. No ifs, ands, or buts. As you said, however, even non-combustible materials -- like water in your classic example -- can create some violent tank failures that meet the other, unofficial definition of BLEVE: Blast Leveling Everything Very Effectively.

With non-combustibles all you get is the BLEV without the E(xplosion). You do get some pretty impressive catastrophic container failures but they aren't BLEVEs.

Pardon me:

NFPA 921 Section 21.2.2 BLEVEs

The boiling liquid expanding vapor explosion (BLEVE) is the type of mechanical explosion that will be encountered most frequently by the fier investigator. These are explosions involving vessles that contain liquids under pressure at temperatures above their atmospheric boiling points. The liquid need not be flammable. BLEVEs are a sub-type of mechanical explosions but are so common that they are treated here as a seperate explosion type. A BLEVE can occur in a vessel as small as disposable lighters or aerosol cans and as large as tank cars or industrial storage tanks.

Check out the definition of mechanical explosion. Pet peeve or not, you have a misconception about BLEVEs that could bite you in a deposition.

[DeputyChiefGonzo]

The Massachusetts Firefighting Academy has a prop in the gas school that has a alows the student to hear and see what happens when a relief valve activates.

It is a "tank within a tank". The outer tank contains water that provides jacket of for the inner tank, which contains propane gas. When the outer tank is heated up enough to cause pressure in the inner tank, the relief valve for the inner tank opens up. When the gas released by the relief valve ignites.. wowsers!

Deck guns are then put into operation to cool the tank. When the outer tank is sufficently cooled, the releif valve of the inner tank closes. Of course the flow of gas that fuels the prop is controlled at the control "tower" and can be shut down in seconds.

It starts as a high pitched whistle... when it ignites, it sounds like an B-1 Lancer with the afterburners kicked in...

[nmfire]

A relief won't always whistle just because it is open. It might be blowing off pressure and just making the usual wooshing sound. As the pressure increases, the rate of gas flowing through the valve increases. Ever boil water in a kettle? It steams for a while. Eventually the steam pressure forces it's way out of the "valve" fast enough to make a whistling sound telling you the water is hot enough. The same thing can happen to a tank. It's usually a very good sign that your efforts are failing and it's time to get the hell out of there.

Also, george is absolutely correct. Nothing about a BLEVE requires fire. You can have a tank of milk overpressure, fail, and explode. It's still a BLEVE.

[E229Lt]

Ever boil water in a kettle? It steams for a while. Eventually the steam pressure forces it's way out of the "valve" fast enough to make a whistling sound telling you the water is hot enough.

Great example!

The open relief valve does, in fact, have a sound of escaping product but when the high pitched whistle begins, it is a sign that the valve is no longer compensating for the pressure build up and a failure is imminent.

Now the tough part:

I agree 100% with George, a closed container of water or any other non-flamable liquid can BLEVE.

[EFD840]

SkipJack270,

Everyone's given very good explanations and I'm not going to try to better them. I will add that if you get a significant fire in a food storage area, look around the debris and you will probably find the remains of several BLEVEs.

Canned foods often contain lots of liquid and those cans don't have a relief valve. Get them hot enough and they'll pop and take off with an amazing amount of force.