It would depend on the exact type of petroleum product being shipped, how full the container was and whether there was oxygen in the empty space. As I understand it, tanks for transporting flammable liquids (ie, fuels) are purged of oxygen before shipping to avoid the risk of sparks causing explosions. There is an atmosphere of inert gas over the petroleum products at all time. This would prevent an explosion, since petroleum product produce energy by being oxidized, something they cannot do alone, under an inert atmosphere.

It would also require that a projectile penetrate outer the hull of the ship and the side of the tank containing the petroleum product. If the pirates brought a 14.4mm machine gun with them, this might be sufficient, but I doubt anything less will penetrate the outer hull of the vessel. Although the outer hull might be penetrated by an RPG-7, the outer hull will shield the inner tank wall much like slat armor shields a vehicle- the separating space between the two barriers will allow the gaseous penetrator to dissipate. Even if the space were modest (say a foot or two), this would probably be enough to defeat any HEAT warheads small enough to be launched from a man-portable platform.

Additionally, even in an oxygen atmosphere, crude oil is not particularly volatile nor is the diesel/kerosene used to run most large ship motors. They might burn if the "fuel tank" of the vessel were pierced, but they wouldn't EXPLODE. Also, there will be fire suppression systems in the engine room, or at least their should be.

The gods of such questions are Adam Savage and Jamie Hyneman and they say, basically, no.

At least about gasoline. Which makes sense, as gasoline is only inflammable when mixed with oxygen in a fairly narrow range of proportions.

And, yes, I'd be guessing here, but the same is probably true of LPG and especially crude oil. Don't forget, the bullet would have to be
1. fired
2. hit a tank with the fuel in it
3. penetrate the tough metal of the tank (which is designed to contain high-pressure fluid in heavy seas)
4. bring enough heat to ignite the fuel
5. somewhere find enough oxygen to support a fire

Basically, this is only going happen on an episode of 24.

That wouldn't work, for reasons that should be obvious from my first post. LNG isn't an explosive, it's a relatively slow-burning petroleum fuel. If it were under a lot of pressure, shattering it (with a ton of explosives) would probably throw quite a bit of debris. It would also make quite an impressive fireball as it burned in the air. But it would not explode as if it were a tanker filled with nitroglycerin.

Tankers full of explosives have gone off in harbors before and it caused horrific damage. Here's one:
http://en.wikipedia.org/wiki/Halifax_Explosion

There have been others (and even a few from torts that I can't remember the specifics of) but I can't remember them off the top of my head.

Capture a liquid natural gas tanker, wire it with explosives, and sail it into a busy harbor. Ask for a few hundred million bucks.

For the same reasons that suicide hijacking doesn't work any more, this won't, either.

You know, we have these things called navies and coast guards that don't let them come in. I am reassured that the current C-in-C appears to have remembered why the hell we have a navy.

Kopel, you should keep in mind that explosions and fires are very different things. Roughly speaking, an explosion only happens when the chemical reactants are well-mixed, so that the chemical reaction can happen over a large volume simultaneously. (It doesn't actually happen simultaneously, of course; it begins somewhere with an application of the necessary activation energy, and then a wave of reaction radiates out from there, its speed limited only by the speed at which mechanical energy can propagate in the material, roughly the speed of sound.)

A combustion, by contrast, exists when the reactants are not well-mixed, and one or more must be transported to some interface, typically by convection, i.e. actual mass transport, a considerably slower process than energy transport. A tank of liquid gasoline burns at the surface, and gas and oxygen must be transported to the interface to react. By contrast, if the gas is mixed as vapor with the oxygen, the reaction can take place throughout the volume immediately, and you can get an explosion.

Clearly a bullet can provide activation energy, but that will only get you an explosion if your reactants are pre-mixed. Of course, ships are carefully designed to avoid any mixing of chemically reactive species, since events as energetic as a mere bullet impact, e.g. a hundred-pound beam slipping and hitting a steel deck, are not uncommon. (For the same reason, if you leave your stove on but unlit, and your house fills halfway with methane, it's pretty sure to go off, even if you don't fire your gun.)

You're probably also talking about large explosions, and that means substantial amounts of mixing, which requires lots of energy (not mere bullets) and/or lots of time. So I'd suggest that the only way a bullet can set off an explosion is if some disastrous pre-existing condition has been set up -- and in that case, you probably won't need a bullet to set off the explosion anyway.

About starting a fire I have no idea. Starting fires isn't very hard, I would guess. You could just hit a fusebox, maybe.

I spent 2-1/2 years on a fleet oiler carrying 8 million gallons of DFM (Diesel Fuel, Marine) and JP5 (jet fuel -- basically kerosene). Neither is particularly volatile, although it's not a good idea to test that statement by dropping matches into the tanks.

Distinguish LPG and LNG, which some refer to. LPG is a conventional petroleum-based fuel. LNG is Liqufied natural Gas, which is cooled to several hundred degrees below zero farenheit. There are apocalyptic scenarios with this, but it requires a large spill, the gradual warming and then vaporization of the fuel (which would come out as a supercooled liquid and then change to a gas that is heavier than air at first) and then an ignition source. In the scenarios, it is the most spectacular but also the most difficult.

I don't believe the thermobaric bombs use fossil fuels as combustible, but I believe the principles are similar.

What Tom S said.

I was in the Persian Gulf during the 'Tanker War', working with the US Navy's Public Relations guys. They were concerned about RPG attacks on tankers--particularly LPG carriers--but not overly concerned. There was a certain amount of gallows humor about 'Giant Ronsons', but no actual experience of them.

We had a LNG spill outside of Brenham in 1992. Conditions were just right as it was a cool still morning and the gas escaped and stayed near the ground in a shallow valley. It hit a source of ignition and created a huge explosion. I heard it in Houston, about 80 miles away. It broke windows several miles out.

My history professor in college was with an Army unit that went to Texas City to help following that blast. He could tell captivating stories about it.

The Darwin Awards web site chronicled the story of a man who shot a butane tank with a .22 and then walked towards it with a lighter to see how close he could get before it ignited.

The navy and Marines train people to board ships. So does the Coast Guard. In fact the Coast Guard does it all the time. We don't train them to board with water pistols.

Could an academic with too much time on his hands dream up a scenario leading to catastrophe? Yes. Is it likely that every ship with an armed crew is sailing to certain doom as their idiot crewmembers pour hundreds of armor piercing incendiary rounds into paper thin containers filled with highly unstable high explosives? No.

What about a direct hit to a LNG tank from an RPG. You have the whole, essentially burned into tank...

Just got off the line with my father, who's a fire/explosion investigator. If a round has punctured a tank containing an accelerant, it is almost certain to be throwing off enough heat as a result of the friction to ignite the fuel. And if a sizable tank goes on any ship, the ship will be a total loss.

http://www.youtube.com/watch?v=wVZUVsHsWis

Remember: there's nothing that says the firefight would have to be inter-ship. If it takes place after the pirates board (as the scuffle did on the Maersk Alabama), then the requisite firepower to create an inferno is much lower.

Additionally, the most recent pirate attacks have involved, among other weapons, hand grenades. An incendiary device that finds a pool of accelerants will be sufficient to cause a fire, and a well-fueled shipboard fire areas can burn incredibly hot, which in turn increases the risk of combustion in nearby areas.

This scenario doesn't make a lot of sense to me. You can have a lot of damage caused by fire, but explosion is a different matter.

There is a second issue that I can think of though. Imagine if pirates captured an LNG tanker in a convoy (per CHris99's suggestion, some armed crews but no military escort) and threatened to start ramming ships if there wasn't a surrender. Could the real or perceived threat from this sort of tactic allow pirates to end up holding a lot more ships hostage?

Another question involves possibilities of shaped charges in terrorist attacks on tankers. If Somali pirates develop ties to Al Qaeda would this be a possibility?

TomS.
Polisario had a navy. Hadn't heard.
Question is what was the goal in attacking fishing boats. Destroying them or scaring them into staying ashore, or capturing them? If the latter, 14.5s and RPGs are not cool. A heavy MG round going through, say, wood or fiberglass and hitting the engine block means you have converted a motor-driven commercial vessel of some use to a raft.
The extra punch of a heavy MG is unnecessary for the piracy we see, and awkward to use, especially when close to the merchie. All downside.
I presume the Polisario didn't worry about having to explain the mount?

@ einhverfr

There is a second issue that I can think of though. Imagine if pirates captured an LNG tanker in a convoy (per CHris99's suggestion, some armed crews but no military escort) and threatened to start ramming ships if there wasn't a surrender. Could the real or perceived threat from this sort of tactic allow pirates to end up holding a lot more ships hostage?

They could do the same with any freighter, albeit with less spectacle. Once a weapon like that is on the loose, it would be a trivial task to put a torpedo or a laser guided bomb into it.

Another question involves possibilities of shaped charges in terrorist attacks on tankers. If Somali pirates develop ties to Al Qaeda would this be a possibility?

An RPG uses a shaped charge warhead. A shaped charge, assuming it is fired such that it penetrates the fuel tank, makes rather a small hole. You’ll have a nasty blowtorch fire. There isn’t enough power in the warhead to rupture the tank.

During the Tanker Wars in the Persian/Arabian (depending on whose side you’re on) Gulf, the Iranians found it difficult to damage large tankers with dedicated antiship missiles such as Exocets. Big ships are remarkably tough critters.

If a real navy were to attack large merchant vessels, the attack would preferably be made with torpedoes or large aerial bombs. Five inch guns would make a mess of a tanker, but it would take a lot of five inch fire to sink a freighter.

POLISARIO claimed that they were "protecting" the territorial waters of the "Saharwi Republic" against illegal fishing. The fishing boat crews were held hostage, often in return for their home country making political concessions to POLISARIO, such as allowing POLISARIO to open an interests office (Spain).

Until Morocco was able to keep POLISARIO out of the Western Sahara through the use a system of sand wall fortifications, POLISARIO had pretty much free run of the territory.

Iraq used Exocets, not Iran.

Former deck officer (chief mate), maritime academy education, served on tankers (crude and product), bulk cargo vessels, container ships and self-propelled dredges—

1. Penetration of a fuel tank is unlikely (they're typically—though not always—below the waterline at normal drafts for most ships), the fuel is very heavy (closer to tar, must be heated to flow), and can be difficult to burn without substantial pre-heating. The engine room portion of the ship has other stuff that could, in theory, burn (lube oil, hydraulic fluid, diesel) but is unlikely in practice.

2. Crude oil is very flammable if exposed to oxygen; however, penetration of a cargo tank is unlikely. Virtually all ships are double-hulled (OPA '90) to reduce the possibility of spill resulting from collision or allision (thank Joe Hazelwood), so the round would need to penetrate the outer hull plating, travel through a ballast tank or other void space and retain enough energy to penetrate the cargo tank plating. I suppose a large enough round (.50 BMG) might manage to do so, but the spill would likely be confined to the void space. The cargo itself is maintained in an inert (non-flammable) environment within the cargo tank. If spilled into the void space, the atmosphere would quickly become too rich to support combustion.

3. I've never served on an LNG ship, but my reading (perhaps out of date by now) would again lead me to believe that penetration into the cargo tank is unlikely (again, absent a very energetic round such as a .50 BMG). The liquid is maintained in a cryogenic environment, a hence the cargo tank's walls are fairly thick and well insulated.

4. Virtually all types of cargo are carried by ship. Many of these cargoes could be hazardous, flammable or explosive, but as a general rule one may assume that exceptionally hazardous cargoes are carried with much greater care. Chemical product ships carrying ethers, alcohols or other cargoes with very low flashpoints, or exceptionally poisonous cargoes (e.g., cyanates, benzene) are double hulled, with greater subdivision of tanks and more exotic inerting systems, for example. I believe it unlikely that typical small arms fire could penetrate these cargo tanks.

Pirates seem to favor RPGs, at least for intimidation. I don't know anything about RPGs, have never spoken to anyone that has first-hand experience with them, and so I can't really comment about them. They seem pretty potent (at least the armor-piercing anti-tank variety) and it's possible that they could penetrate into a cargo tank with enough energy to create a sizeable spill that could be ignited from a random spark. I couldn't say.

I pretty much agree with C/M except that, in the context of a double hulled merchant vessel, a .50 BMG or 12.7mm is not a particularly energetic round. A four inch gun is considered a popgun at this scale.

A shaped charge round like an RPG depends on the warhead exploding at the optimal distance from the target. The copper lining of the conical charge is explosively formed into a rod of plasma that penetrates the armor. Change the distance, and the effectiveness drops off dramatically. That's why the glorified bedspring slat armor, retrofitted to armored vehicles, works. It detonates the warhead too far away from the real armor to allow it to penetrate.

So the effectiveness of a double hull will depend on the standoff distance and the thickness of the inner hull.

Once the shaped charge penetrates, it has punched a small hole in the armor. It destroys a tank by spraying the armor and the penetrator rod around the inside and setting things on fire or penetrating them with white hot fragments. You definitely don't want to be in there. In a fuel tank, that hot plasma is quickly quenched with cold oil. WW-II battleships used their fuel tanks, in part as armor.

So you now have a two inch hole leaking black oil. You send down a crew with a tapered wooden peg and a mallet. Seriously. If it's a LPG tanker, you have a blowtorch fire, but that's still controlable. There's no way an RPG is going to reupture a tank or do serious damage to a merchie unless some poor mope is standing in the wrong place.

RPGs are effective against tanks because the inside is tiny.

Normal copper clad or lead bullets will not generate a spark to cause ignition. A steel core bullet (as often seen in some military ball or armor piercing ammunition)could generate a spark but even then ignition depends on other factors such as fuel/air ratio etc.

Upshot: Very low risk of explosion or fire.

First, large ships have hulls that are several inches thick. Oceanic waves can be so large that even a super-tanker will sometimes be lifted by one wave in the middle with both ends hanging, alternating with being suspended between two waves with the middle hanging. It's not the framework that takes such loads, but the hull plating forming what is in essence a giant box beam. So .30 caliber weapons are no threat to the ship itself, although they might be quite useful to keep the crew back so they can't use firehoses to repel boarders. A .50 machine gun may or may not penetrate, but penetrating the hull and then the inner tank on a tanker seems pretty unlikely. RPG's with shaped charges should easily burn a hole through the hull, but I'd expect the directed blast to dissipate in the inter-hull space.

OTOH, if it's a single-hulled freighter loaded with grain, cotton, or other flammable cargo with airspaces (not to mention things like WP), I see a pretty good chance of an RPG igniting the cargo, and not much chance of the crew repelling pirates and controlling the fire at the same time. The crew would have to take to the liferafts and the insurers would take a big loss, but the only explosion hazard would be if the crew left the hatches dogged down so tightly that pressure built up.

Finally, if crude oil burned that easily, we wouldn't have so much trouble controlling oil spills. Just evacuate and flick a match. But actually, while a burning oil slick can be deadly to men in the water or small boats, and would thus drive off all rescue or salvage operations, it burns out long before the fuel is gone. And it's not explosive.

With petroleum distillates much lighter than crude or the bunker fuel used in steamships (a petroleum fraction just lighter than tar, often needing heated so it can be pumper), there is an explosion hazard if the inner hull/tanks are leaking into the space between the hulls and the spill is vaporizing faster than the ventilators can exhange the air. If the concentration reaches the right level, and then there's something to ignite it, *boom*. I think that a .50 BMG bullet coming through the outer hull would be hot enough from penetrating steal plate for ignition. But for this scenario, the pirates would have to attack once, with something heavy enough to penetrate both hulls, be repelled, and come back later for another try, after enough time for the vapors to build up, but not long enough for the crew to rig extra ventilation and pound plugs into the leaks. I'd put that hazard much lower than the chance that the pirates would win the first fight and be angry enough at the resistance to summarily execute captured crewmen.