BLEVE in a LPG Pressure Vessel

[Markbnj]

Hi guys. I'm working on a scenario involving the intentional demolition of a large pressurized cargo tank containing a liquefied petroleum gas at or near ambient temperature. Obviously this scenario is a fictional one for analysis purposes. I'm seeking input on the probability of causing a BLEVE event on such a tank of capacity > 1500 M^3 through the use of explosives to initiate rupture of the pressure vessel.

The purpose of the analysis is to describe qualitatively and quantitatively a plausible scenario in which an actor might cause maximum damage by utilizing the cargo of an ocean-going vessel as a weapon.

The cargo I have chosen is Vinyl Chloride Monomer in liquified state, carried at maximum 45 deg. C ambient temperature. The tank(s) are bullet-shaped, built to withstand a maximum pressure of 18 bar-g (257.65 psi). At an operating temperature of 20 deg. C the vapor pressure of VCM is approx. 50 psi. which is the assumed pressure for the development of this scenario. The tank shell and heads are likely constructed of SA 612 carbon steel in a thickness of between 19 - 22mm., with a phenolic epoxy inner coating of 6 mm. At 100% load the tank would contain approximately 1200 metric tons of liquid VCM.

A simple mass release of this material would be bad enough, as VCM has a number of noxious immediate effects and potential long-term health risks. In addition it is explosive in vapor form, and has the potential to polymerize explosively under certain conditions. This material was chosen for the scenario over materials like methane, butane, and propane because of its additional toxicity concerns, as well as the fact that much less attention is paid to it over the more ominous LNG/LPG cargoes of the moment, which are probably much safer (certainly so in refrigerated ambient-pressure carriage scenarios).

To up the ante I am postulating the actor attempting to cause a BLEVE or BLEVE-like event by cutting the fully-loaded tank using explosives. A BLEVE, for those unfamiliar, is a Boiling Liquid Expanding Vapor Explosion. In a BLEVE event warming of a pressurized cargo, perhaps due to external fire) proceeds to the point where the pressure vessel ruptures. If the rupture extends across a significant portion of the tank the contents may depressurize catastrophically forming a huge expanding vapor cloud. The cloud may or may not ignite. BLEVEs can occur with nonflammable gases such as steam. The initial depressurization provides the concussive damage (in one such event with a railcar the tank was thrown over 300 meters), and if the material is inflammable that may be followed by a fireball. Anyone who has tossed an aerosol can into a campfire has probably seen a BLEVE on a small scale.

The key to a BLEVE appears to be the size of the rupture. With a long rupture you may get a BLEVE, whereas a smaller opening is likely to cause a jet that doesn't result in catastrophic failure of the vessel. In my scenario, rather than warming the contents to the point where internal pressure causes the tank to rupture, I postulate the use of high explosive such as C4 shaped charges, or shockwave refraction tape to essentially take the top off the tank in one instantaneous event.

The technical question is: would this be likely to initiate a BLEVE? The pressure would be much lower than in the warm up and burst scenario, but the explosives would guarantee instantaneous escape of the entire tank load (and possibly ignition). A release in Britain a few years back of just 600 kg of VCM caused a huge vapor cloud which fortunately did not ignite (although it did polymerize all over the vessel and dock).

Any insights would be appreciated as I am trying to make the scenario as plausible and realistic as possible.

 

[CycloWizard]

I've never heard of BLEVE before, but the first thing that comes to mind is that the hole should be designed such that the rate of evaporation outpaces the rate of outflow through the hole, resulting in a pressure buildup within the tank. As long as the pressure within the tank keeps increasing, the flowrate out of the tank will also increase, so the evaporation rate should be significantly higher than the outflow rate, which seems to indicate that a small hole is better. More than that will have to wait until tomorrow.

 

[Markbnj]

I don't precisely understand the dynamics, but work by Dr. Birk of Queen's University in Canada has shown that the size of the rupture is critical in whether a BLEVE initiates. Small holes seem to allow pressure release without failure of the vessel, while at some longer length the depressurization is just rapid enough to blow the more substantially weakened vessel apart.

http://me.queensu.ca/people/bi...ve/queensbleve9296.php

My scenario doesn't allow for any sort of determination of what the exact rupture dimensions need to be, because no such calculation exists as far as I know. So I am postulating an overkill method where we just slice the top off the pressure vessel in one blow.

 

[CycloWizard]

But if you slice the top clean off, where will the pressure buildup come from? I suppose you could boil everything using a simple heater before you blew off the top, but that's almost cheating. I'm not an expert in fracture mechanics, but I do know that the shape of the hole is extremely important in inducing failure. If the curvature is very large (i.e. a sharp corner or tear), then stress concentration occurs and leads to crack propagation. I still haven't thought it through very much, just throwing out ideas. I probably have a book that talks about how to avoid BLEVE failures somewhere around here, so I'll have to dig that out later.

 

[Markbnj]

Thanks a lot for your thoughts. BLEVE-like is probably a better term for what I am thinking will happen, bu this is really my central question. The entire load (at 50 PSI) will certainly gasify when the pressure vessel is opened, but the boil out would not be as violent as in the case where the internal pressure builds up to a couple of hundred PSI or better.

 

[CycloWizard]

I got a little more interested in this and opened up my handy-dandy book entitled "Chemical Process Safety," (Crowl and Louvar, 2002). I'm not sure how the mods here feel about quoting sections of copyrighted material, so I'll just give the overview, which is just about what I already said, but I think this gives some additional insights.

BLEVE occurs when a tank containing a liquid above its atmospheric pressure boiling point ruptures, resutling in the explosive vaporization of a large fraction of the tank's contents. They are caused by sudden failure of the vessel, usually due to fire. If the liquid is flammable and a flame source is present, it may turn into a VCE (Vapor Cloud Explosion). VCEs are basically more violent BLEVEs, since the combustion essentially causes additional heating and, therefore, more damage and more fireworks (which would be great for a movie ). The book says "Often, the boiling and burning liquid behaves as a rocket fuel, propelling vessel parts for great distances." The book also gives methods by which one can estimate the fraction of the liquid that will vaporize. I know that there are also ways to predict the characteristics of the explosion, as every chemical engineer learns in his design classes.

 

[Markbnj]

Thanks for the tip, CycloWizard. I will hunt up that book. There are a couple available specifically on the nature of marine pressurized vessles for liquified gas, but they are published by the classification societies and run a couple hundred bucks each. The key aspect of the BLEVE event is obviously the build-up of pressure in the vessel, and then the nature of the rupture in the vessel wall. I now doubt that the standard carriage pressure of 50 PSI is enough, so I am hypothesizing the use of bunker fuel in the hold to heat the tanks. Still working on it.

 

[spelletrader]

You should be looking more into a thermobaric (AKA HITS, FAE, FAX) effect, rather then BLEVE. Assuming you want precision and lethality (IE an effective weapon) in a controlled situation, then get away from the BLEVE idea. With a thermobaric event you can assure that you use the majority of your fuel and expand it to maximum effective range, where as a BLEVE would be unpredictable, at best.

To achieve this you would want to use Flexible Linear Shaped Charge (FLSC) to rupture the canisters (can't get into grains per foot of the FLSC without knowing the case thickness and wall strength) and a secondary charge (any explosive with a brisance =/> TNT should be fine) to travel with your cloud and timed to go off when the cloud has reached its maximum range. Looking at the flash points of your material the FLSC may actually ignite it as it expands, which is not ideal, but given the quantity of material it should still have time to expand quite a bit.

If you want to get into specifics I will need some credentials and a whole lot more information.

 

[CycloWizard]

Originally posted by: spelletrader
You should be looking more into a thermobaric (AKA HITS, FAE, FAX) effect, rather then BLEVE. Assuming you want precision and lethality (IE an effective weapon) in a controlled situation, then get away from the BLEVE idea. With a thermobaric event you can assure that you use the majority of your fuel and expand it to maximum effective range, where as a BLEVE would be unpredictable, at best.

To achieve this you would want to use Flexible Linear Shaped Charge (FLSC) to rupture the canisters (can't get into grains per foot of the FLSC without knowing the case thickness and wall strength) and a secondary charge (any explosive with a brisance =/> TNT should be fine) to travel with your cloud and timed to go off when the cloud has reached its maximum range. Looking at the flash points of your material the FLSC may actually ignite it as it expands, which is not ideal, but given the quantity of material it should still have time to expand quite a bit.

If you want to get into specifics I will need some credentials and a whole lot more information.

You can predict quite a bit about the behavior of a BLEVE, especially if you're controlling the failure of the vessel. You just need to know about the substance that you're boiling.

As for the pressure level in the tank, the higher the pressure, the more impressive the explosion will be, but the more imporant the method of inducing tank failure will be as well. 50 psi isn't really what I would consider a high pressure, and almost any pressure vessel will not fail at such a pressure. I think the important thing would be to raise the temperature above the ambient boiling point, then raise it some more to increase the fraction in the vapor phase (and, therefore, the internal pressure). How much you can push this is heavily dependent on the tank design and the material you're using. If you're thinking about doing this on any sort of large scale, I would suggest doing it in the middle of the desert with no one within a few miles of the tank. In any case, this is definitely not something you would want to attempt without at least one knowledgeable engineering consultant to help you avoid blowing yourself up in the preparation. My fees are quite reasonable, since I'm still a grad student. If you wait until December, they will go up considerably.

 

[Markbnj]

Thanks very much for the additional thoughts. Spelltrader I'm going to do some research on the mechanisms you suggest and see where that leads me. As to the overall question of credentials and intentions, I'm a software developer and author of 25 or so published non-fiction articles on software technology. I'm also an aspiring novelist, and this entire scenario is part of a plot development. There will certainly not be a demo detonation . There will also not be enough information in the story to reproduce any of the effects it describes. However, having the engineering and scientific basis of a plausible threat makes the whole thing much more realistic.

Thanks again for your help, guys.

 

[CycloWizard]

Originally posted by: Markbnj
Thanks very much for the additional thoughts. Spelltrader I'm going to do some research on the mechanisms you suggest and see where that leads me. As to the overall question of credentials and intentions, I'm a software developer and author of 25 or so published non-fiction articles on software technology. I'm also an aspiring novelist, and this entire scenario is part of a plot development. There will certainly not be a demo detonation . There will also not be enough information in the story to reproduce any of the effects it describes. However, having the engineering and scientific basis of a plausible threat makes the whole thing much more realistic.

Thanks again for your help, guys.

NP. Just send me an autographed copy when it's all written up. :thumbsup:

 

[Markbnj]

You got it . I did some additional reading, and it seems that a BLEVE is in fact a specific type of initiation for a thermobaric event. Current advanced weaponry design uses powders like boron or aluminum and oxidizers to create a precise dust/air mix. A BLEVE is the only chain of events I have been able to find info on that will create the right combination when you start with a liquefied gas under pressure. Not only do you have to disperse the material to the right concentration, but you have to boil it off first. In a fuel-air bomb the dispersal charge is centered in the fuel, and vaporizes it so that a secondary charge can ignite it. Current boron or aluminum mixes just have to be dispersed, and so a single charge can do the task of dispersal and ignition.

I think that whatever you call it, the whole scenario here depends on getting the liquified gas boiled off into a vapor state and dispersed out to the right concentration in milliseconds. A BLEVE can accomplish this because of the high pressures achieved. To burst a vessel like that on a ship will require in excess of 300 psi, probably much more. The energy state of the liquified gas is such that once the constraining vessel ceases to exist a shock wave propagates through the liquid gasifying it nearly instantaneously, at the same time pushing it outward. I don't know if it is reasonable for malicious actors to think they can reliably reproduce this effect.

But on the other hand I'm not sure they have to to have the effect they want to have. If you blow the tops off huge pressure vessels full of VCM you're going to get one hell of a gas cloud of toxic material. Rather than the expanding ball of a BLEVE you'll probably get a massive gush of gas flowing away from the ship's hull along the water in the direction of the wind (if any). That cloud will then disperse as it warms, but there would be the potential for ignition. Just as importantly, the psychological affect of that kind of release, and the potential long-term health effects, would be significant. It's also unlikely that responding officials would have the time or ability to reason through to these conclusions. They would call in experts but probably would act on the assumption that the actors can produce a big bang.

 

[Markbnj]

Just a quick update to let you guys know how this is coming along. Based on my research so far I'm becoming skeptical that any scenario involving pressurized LPG, either heating to induce a BLEVE or some kind of explosives-initiated thermobaric event, can really be considered plausible. For all the attention we're focusing on these vessels, it doesn't seem to me that they are the real threat. The outcome is too difficult to predict and the effort too complicated. There might be enough additional psychological leverage from sitting on 3000 M^3 of VCM to make it wortwhile, but for the moment I've shifted my attention to worldwide bulk shipment of ammonium nitrate prills. Vessels carrying bulk ammonium nitrate also carry large amounts (up to 200 mtons or more) of marine diesel fuel, and many more mtons of bunker fuel. So my current research focuses on the feasability of mixing these agents in the hold at sea. Surprisingly the ANFO mixing process seems to be very tolerant, such that spraying the diesel over the cargo and using some PVC pipe to facilitate introduction deeper into the cargo might actually work.

It's kind of frightening, actually. For an example of what this might mean see wikipedia's article on the Texas City disaster.

That detonation was caused by exothermic decomposition of the fertilizer and subsequent heating. An ANFO detonation would be much more energetic I think.

 

[imported_Tick]

I would personally like to see a novel where the terrorists utilize an underwater explosion. It's got that cool and different aspect, and it makes some sense. I doubt that an ANFO storage containers offer much confinement. Also, think of how cool a "tidal wave" would be in, say, San Francisco bay. They could scuttle the ship just before hand, and then detonate at the appropriate depth.

 

[Markbnj]

That's a very interesting take on it, Tick. If I do that I'll give you credit .

 

[spelletrader]

The main problem with ANFO is that it requires a proper mix and a good booster to ensure that it detonates efficiently. Otherwise you end up with large quantities deflagrating rather than detonating. Also keep in mind that pre-mixed ANFO that is designed for commercial blasting is only around 80% as powerful as TNT (with some varieties that are mixed with different fuels reaching 160% TNT equivalent). I highly doubt you would reach anywhere near this level of quality in an improvised environment. Obviously the quantities on board will overcome most of these issues, but keep them in mind when doing blast calculations.

There is precedent for creating a large wave with ship board explosives. Check out the Halifax explosion of WWI, a ship called the Mont Blanc. If I remember correctly, it was carrying near six million pounds of various explosives. It collided with another ship, caught fire, pulled into port and detonated a short time later. The resulting wave was somewhere near 20 meters high.

If you wanted to detonate under water you would have to find a way to sink the ship while maintaining the integrity of the hold where the ANFO was located. It is extremely hydroscopic, and you would lose almost any hope of detonation if the hold was to flood.

There are lots of very interesting things that can be done with explosively driven water, you have a scenario that can make for a very interesting read. Try to do it justice! =)

 

[imported_Tick]

Originally posted by: spelletrader
The main problem with ANFO is that it requires a proper mix and a good booster to ensure that it detonates efficiently. Otherwise you end up with large quantities deflagrating rather than detonating. Also keep in mind that pre-mixed ANFO that is designed for commercial blasting is only around 80% as powerful as TNT (with some varieties that are mixed with different fuels reaching 160% TNT equivalent). I highly doubt you would reach anywhere near this level of quality in an improvised environment. Obviously the quantities on board will overcome most of these issues, but keep them in mind when doing blast calculations.

There is precedent for creating a large wave with ship board explosives. Check out the Halifax explosion of WWI, a ship called the Mont Blanc. If I remember correctly, it was carrying near six million pounds of various explosives. It collided with another ship, caught fire, pulled into port and detonated a short time later. The resulting wave was somewhere near 20 meters high.

If you wanted to detonate under water you would have to find a way to sink the ship while maintaining the integrity of the hold where the ANFO was located. It is extremely hydroscopic, and you would lose almost any hope of detonation if the hold was to flood.

There are lots of very interesting things that can be done with explosively driven water, you have a scenario that can make for a very interesting read. Try to do it justice! =)

Isn't the cargo hold going to be it's own seperate water tight compartment? If so, then the terrorists could just blow all the other compartments with scuttling charges, thus leaving nice, dry, anfo. Also, I'm thinking that any group can smuggle on a couple hundred pounds of TNT for a booster. Neither of these problems seems crippling to me.

 

[spelletrader]

Tick,

It would not just be booster size, also locations. You would not want one large charge located in one location. You would want multiple charges placed at proper intervals. Not a challenge to get explosives on board, just to stay true to reality as Mark wishes.

Yes you can keep the holds airtight, however air in the holds means buoyancy. I am not at all familiar with marine cargo vessels of the type that transport Ammonium Nitrate prills, so I have no idea if it is possible for one to sink without the holds being flooded.

Also I am not sure that you would cause greater damage with a strictly underwater detonation. While the displacement of water would be greater, resulting in a larger wave, the blast would have little to no effect above surface. The displacement would result in a wave going in all directions from the epicenter (think dropping a rock in a pond) so not all of the energy would be directed toward to shore. This could be very effective in a bay or harbor, not so much near open waters. Another idea might be to detonate under water near a major fault line? Totally out of my realm of experience, but interesting to me.

Mark, what is the overall target and/or scenario?

 

[Markbnj]

Originally posted by: spelletrader
The main problem with ANFO is that it requires a proper mix and a good booster to ensure that it detonates efficiently. Otherwise you end up with large quantities deflagrating rather than detonating. Also keep in mind that pre-mixed ANFO that is designed for commercial blasting is only around 80% as powerful as TNT (with some varieties that are mixed with different fuels reaching 160% TNT equivalent). I highly doubt you would reach anywhere near this level of quality in an improvised environment. Obviously the quantities on board will overcome most of these issues, but keep them in mind when doing blast calculations.

There is precedent for creating a large wave with ship board explosives. Check out the Halifax explosion of WWI, a ship called the Mont Blanc. If I remember correctly, it was carrying near six million pounds of various explosives. It collided with another ship, caught fire, pulled into port and detonated a short time later. The resulting wave was somewhere near 20 meters high.

If you wanted to detonate under water you would have to find a way to sink the ship while maintaining the integrity of the hold where the ANFO was located. It is extremely hydroscopic, and you would lose almost any hope of detonation if the hold was to flood.

There are lots of very interesting things that can be done with explosively driven water, you have a scenario that can make for a very interesting read. Try to do it justice! =)

All good points, spelletrader. I'm familiar with the Mont-Blanc incident in Halifax, and in fact I have been to the museum there twice and seen the displays and an incredible diorama of the whole event. The Mont-Blanc was loaded with a particularly volatile combination of nitrocellulose, picric acid, and an incredible 200 tons of TNT and 35 tons of Benzol. Quite a combination.

The incident of the Grandcamp in Texas City, TX gives a better indicator of what ammonium nitrate is capable of, and it is certainly less than what the Mont-Blanc did to Halifax, but nonetheless devastating. The Grandcamp was loaded with granularized ammonium nitrate. The detonation was due to heating and eventual rapid decompisition.

ANFO, on the other hand, while needing an HE booster, does get you to a detonation velocity of 13k fps or so. TNT, of course, is nearly twice that, but as you note quantity can make up the difference. The Grandcamp had 8500 tons or so of granularized ammonium nitrate on-board. The scenario I am thinking of would involve one hold of a dry bulk vessel, approximately 1500 - 2000 tons of material. By way of contrast, McVeigh's bomb in Oklahoma City is estimated at no more than 2.5 tons.

I did a fair bit of research on the mixing, and here's where it gets interesting and a little frightening: the mix is actually rather tolerant. You need 6-8 percent fuel oil by weight. If we assume 1500 tons of material that equates to 90 tons of fuel. The average dry bulk freighter carries in excess of 150 -200 tons of marine grade diesel oil, and another 500-900 tons or more of HFO bunker fuel. That latter is probably too difficult to handle, but there is enough diesel on hand.

What's necessary is to make sure the oil permeates the load and coats the prills. Too much oil just causes excess vapors without reducing the force of the explosion. Too little degrades the reaction. So the emphasis is to get a lot of diesel into the hold and make sure it flows. I've been puzzling over the best way to do this, and I think there are a few. I didn't mention earlier, but I was a seaman at one point in my life, and am well familiar with commercial vessels. There's enough hose on board a freighter to get the diesel pumped up to the deck. One idea is simply to bring aboard a bunch of additional hose and lay it out on the cargo pile as a soaker. Another is to augment this by driving lengths of perforated PVC pipe into the pile. The cargo depth is going to be in the neighborhood of 40-50 feet. Capillary action will help distribute the fuel. Even if you can only soak the top 15-20 feet, you're looking at maybe 600 tons of good quality explosive contained in a strong and more or less airtight container. The other 900 tons of mostly dry nitrates would just add to the mix when the top layer goes off.

As for the booster, these guys are terrorists, so I am assuming they can get ahold of some semtex, or ordinary dynamite. The upside of requiring a booster charge is the inherent stability of the mix; the ship isn't going to go up until they want it to.

The other aspect of this that is frightening is simply the question of what to do if the threat materializes. Unless you catch the vessel at sea you're in trouble pretty much anywhere on the coast it goes. Say I hijack a 450' dry bulker (maybe 10k gross tons), reprogram the AIS to give a different IMO number, cargo, origin port, and destination, and then drive it toward the Chesapeake. If I want to be really sneaky I'll buy an old, but faster and smaller vessel to do the hijacking, then I will put the crew of the bulker aboard that vessel along with their EPIRB and scuttle her. As far as the rest of the world knows the bulker sank, and they'll find bodies of crew to confirm it, and side-scan sonar will show some lumps of metal on the bottom too. If I do it in deep water I could have 2-3 weeks before they know she's still afloat. Maybe more.

If someone doesn't catch on and make a decision to take me out before I get to the Bay Bridge then little can be done past that point in the face of my threat to light the thing off. The CG is likely to challenge me maybe 10-15 miles out at most. What if I just don't answer? They aren't going to immediately order a strike from Patuxent on my engine room. I'm doing 12-14 knots and I'm an hour out. They will likely bring a cutter up and order me to stop. Cutters do 18 knots, so we rendevous somewhere around... oh... 5 miles out. At that point I can stall them with a little bull about waking the captain up, whatever. They get impatient and order me to stop again. What are their alternatives if I refuse? The cutter isn't going to disable a 450' dry bulk freighter with its 25mm or .50 cals. I'm less than 30 minutes from the entrance to the bay bridge, and they still don't know if I am malicious or just crewed by a bunch of Moroccans who don't speak english. They'll threaten some more, and then escalate when I fail to comply.

The only thing they can do is bounce the situation up the chain. My cargo shows as stone dust or some other harmless commodity, and they have no reason to suspect otherwise. Nevertheless, I'm supposed to stop at the pilotage area off of Cape Henry and take on a pilot since I am not U.S. registered in coastal trade (the U.S. moves the stuff around on rail cars, and maybe sometimes barges, but plenty of African, South American, and Asian nations import the stuff in dry bulk). When I fail to stop for a pilot I am a mile or so from the entrance to the bay, and already within striking distance of the U.S. fleet at Norfolk. Or if I want to make a really strong political statement I'll sail her up the Potomac; there's 22-25 feet of water all the way through to downtown DC, and the entire length of the river is populated enough that any ongoing threat to detonate is a serious one. At that point, of course, they would have to accept the lesser evil and send the Navy to fire on the ship, at which point I would blow it. The game would be to see how close to DC I can get.

Why hasn't it already happened? I don't know. The airliner thing didn't happen until it happened, but we had 25 years of hijackings to show that a malicious party would get control of one if they wanted to. Take a look at the rise in the incidents of high-seas ship hijackings in the last few years. Pretty sobering. Crews are starting to fight back, but still its ridiculously easy for a trained, determined group to grab a ship.

Isn't the cargo hold going to be it's own seperate water tight compartment? If so, then the terrorists could just blow all the other compartments with scuttling charges, thus leaving nice, dry, anfo. Also, I'm thinking that any group can smuggle on a couple hundred pounds of TNT for a booster. Neither of these problems seems crippling to me.

Yep the hold would definitely be watertight, more or less, immediately after you perforate the other compartments. All that's necessary to sink most dry bulkers is to flood the forward two of the four or five holds. However, unless you did it in shallow water the other holds probably would not stay watertight on the way down. The structure of the ship will tear itself apart as she sinks, especially if she is fully loaded and goes down by the bow. Breaking in half as she goes is rather likely.

All in all, while an underwater detonation would be spectacular, I think it's a more complex and risky scenario as compared to just driving a ship somewhere and blowing it up.

 

[jagec]

OK, I just finished talking with a guy who used to do testing of diesel fuel tanks (like on semis). He mentioned BLEVEs, and how spectacular they were..."like a mini-nuke...the guys loved lighting those things off." The way he would do it is to use a balloon burner to heat the tank fairly uniformly. At first they had problems where the aluminum at the top of the tank (where the diesel wasn't touching) would melt before the tank really got up to pressure, but then they added a flame barrier to equilibrate things a little more. Sure enough, once the diesel got hot enough (the often-inadequate pressure relief valves futilely spilling diesel in an attempt to prevent the inevitable), the pressure would be too much for the tank, and it would blow through the softest (hottest) portion of the tank. The sudden drop in pressure would cause the remaining liquid to flash to vapor, and then KABOOOM. Impressive.

I had a response typed up that pertained to the ship scenario you posed, but then the paranoid side of me said I should probably delete the juiciest details. Needless to say, it's scary how easy such a thing would be to pull off.

 

[Markbnj]

The explosion definitely is impressive when it happens. I think the issue with this in a terrorist situation is the risk that it doesn't work. Even in fairly controlled situations a BLEVE may or may not occur, depending on the mode of tank failure. Given the investment in time and money pulling off a stunt like that would require, I think the odds wouldn't be very good. The practical issues of getting a tanker to BLEVE lie with the heating. I've considered the idea of dumping bunker oil into the hold and burning it, as well as bursting/igniting charges, but bunker oil doesn't flow easily unless heated, and bursting charges usually need to be placed near the center of the liquified gas volume.

If you could get your hands on a tanker you would probably be better off running it into a bridge at full steam, or parking it in a harbor and threatening a mass release of fuel or noxious cargo.

 

[ScottMac]

There is a training film used by Fire Departments called "BLEVE" or maybe "B.L.E.V.E" ... that shows a number of real BLEVE events, and discusses the situations leading up to them (and how the FDs handled them).

In the case of the railroad tank car, it took off like a rocket and was found in the next county. Pretty cool stuff.

IIRC (this was a few decades ago), BLEVE generally doesn't create a big explosion (ala blasting components), once the vessal starts to rupture, the gas ignites and it takes off rocket-style (at least most of the time).

There was a recent fire in a Texas (Dallas? I think) city where a propane refilling and storage place caught fire. Again, the main issue they appeard to be worried about was propane tanks flying all over the neighborhood, not massive explosion.

Sounds like you've got in interesting project. Talk to your local FDs about their reaction plan for things like rail-borne LNG/LPG fires, crashes, etc. those fire folks have some pretty good info and resources that you may find useful.

Good Luck

Scott

 

[Markbnj]

Thanks, Scott. If you get an assymetric rupture of one part of the tank then you have a rocket. To get a true BLEVE you need the rupture to occur such that you get a much more symmetrical rapidly expanding vapor cloud followed by ignition. A BLEVE is really just the accidental version of an FAE detonation. FAEs contain all the parts to make sure that success isn't accidental, i.e. a centered bursting charge wrapped by just enough fuel and a tank of the proper strengtht designed to create a perfectly distributed vapor cloud.

I researched this for several months, and at this point I'm not at all convinced you could pull off a large-scale BLEVE using a ship's cargo, at least not in any controllable way. If you filled the hold with bunkers and started it burning I say it's about 10:1 that the ship sinks before the tanks rupture. There are several precedent cases on that. If you cut the tanks with charges you get a release, but only at the holding pressure of the tanks, not the bursting pressure that is reached in a BLEVE. So you don't get as much expansion and the f/a density never gets right: you have a release, not an explosion.

I think you could create much more havoc just driving it into things, frankly, or creating an ecological disaster. I'm still pondering a plot, but I'm left thinking the risk of ships being turned into bombs is very low. Of course, that in itself might make a plot .

 

[PlasmaBomb]

BLEVE video on Youtube

Might be of some interest to you, if you haven't already seen it. Its a video of a test of a Castor rail car beside a BLEVE.

Small Bleve

That has to hurt and the firefighter was probably lucky to be alive...

Styrene Bleve 4000 gallons go bang.