I read this today:
I read somewhere that ~90 ISIS fighters were killed. That doesn’t sound like a dud to me. Perhaps there were some tunnels that survived the blast. I don’t think that’s unexpected.
Should have gone with Jericho.
This. If the tunnel is in loose soil just below the surface, then the blast overpressure might collapse it - but if we’re talking about a hardrock tunnel/cave in the side of a mountain, then the structure of the cavern is well protected from the blast overpressure by thick rock above it. It may indeed be possible for a fatally injurious blast wave to travel down the interior of the tunnel/cave, killing its occupants without significantly damaging the cavern itself.
I thought MOAB was designed to kill by sucking up all of the surrounding oxygen, which it uses for the explosion. Enemies would die of a combination of oxygen deprivation, the blast wave, and incineration, depending on their distance from the explosion. Even if the blast wave did not penetrate far into the tunnel system, the occupants would still die of asphyxiation. In such a case, I would expect tunnels and caves to remain more or less intact.
But I hadn’t paid much attention to the weapon, and stand to be corrected.
They said that’s how it would work, but I’m confused how that would be able to suck air out of the tunnels. I can understand how it can suck up all the air out in the open, but to suck air out of the tunnel it would be creating a vacuum. It seems like the air for the explosion would come from the more free-flowing air out in the open rather than the hard to extract air in the tunnels.
Were I to design a tunnel system, I would not make it airtight. ISTM that when air is consumed by the bomb, that’s where the vacuum is, and it would pull in air from the surroundings – including the tunnels.
That is not the case. The MOAB is simply a shit-ton of conventional explosives in a big ol’ can. The explosive used in the MOAB is also used in some underwater weapons.
I thought it was a fuel-air bomb. I stand corrected.
MOAB is not a thermobaric weapon, designed to use and consume atmospheric oxygen. These devices end up sucking air into the rising fireball, and the negative pressure generated in enclosed spaces makes it hard to breathe against.
MOAB is an explosive device, intended to create overpressure that can also be fatal in enclosed spaces. The ground transmitted shock wave may collapse unstable cave systems.
To really collapse caves you need ground penetration weapons (bunker busters), similar to the Tallboy (5 ton) and Grand Slam (10 ton) weapons used by 617 squadron in WW2. They could be incredibly effective, collapsing tunnels and dropping bridges. They also were used to destroy reinforced concrete U-boat pens, sometimes penetrating 15 feet of reinforced concrete.
The US does have some weapons like this in development - use would be dictated by geography and target value, or maybe the available weapons are currently reserved for other threats.
It’s somehow linked to thermobaric weapons on Wikipedia, based on the Russian Father Of All Bombs being a fuel-air bomb. This has led to much confusion, as looking up the MOAB links to thermobarics, inviting a false conclusion.
I don’t know anything about these things but it seems like a publicity stunt. A single B 52 has a payload triple the weight of a MOAB. Wouldn’t a penetrating bomb (or 30?) be more effective against tunnels in solid rock? Or is the shock wave from an airburst able to kill people underground? In any case, we are asked to believe what the Afghan army our own people are telling us so I think a grain of salt is warranted. Edit: Oops. I see this was address above.
Johnny: in fact, we discussed this in detail. The explosive in MOAB contains its own oxidizer, so it’s not sucking substantial oxygen from the surrounding air. MOAB’s explosive is a bit “rich:” its two main components, RDX and TNT, both have a negative oxygen balance. But H6 also contains roughly 20% powdered aluminum, and there’s no oxidizer included for the aluminum.
H6 was developed as a more stable version of Torpex, which was used in WWII for underwater weapons like torpedoes, mines and depth charges. Wikipedia suggests that the aluminum content prolonged the detonation period but did not contribute directly to the energy content of the explosive. To wit:
“Although both RDX and TNT have a negative oxygen balance, the superheated aluminium component tends to contribute primarily by extending the expansion time of the explosive product gases.”
So the aluminum powder in a MOAB probably burns by combining with ambient oxygen, that’s not why it’s included, and how much of it actually burns is unclear, at least to me. If you wanted the full effect of the aluminum as a fuel/air explosive (FAE), you’d incorporate a little charge to disperse the aluminum into a cloud just before the main detonation, which would then ignite the aluminum. But as it is, the aluminum powder is mixed in evenly with the RDX and TNT, so I’m not certain how much of the aluminum burns and to what effect.
The non-specialist press sometimes called MOAB a thermobaric weapon (CNN did this). I understand “thermobaric” to be essentially synonymous with “FAE” and I gather many others do too, hence the confusion.
Given that “thermobaric” incorporates the Greek roots for “heat” and “pressure,” it is (IMHO) a meaningless term when applied to weapons that go boom: nearly all of them create heat and pressure in the process, so “thermobaric” doesn’t really specify much.
Natural caves don’t always give you a choice, and the additional airflow options may well be restricted for geological or security reasons.
People use caves and bunkers to restrict access to controllable access points - having massive airflow through to protect against thermobaric weapons invites a guided missile through the front or back doors, or a visit from the special forces team.
Thermobaric bombs, CNN thermobaric bombs, and hair dryers are discussed at length in a sidebar in the recent thread First use of Mother of All Bombs: what’s the status of the US arsenal? Lessons learned?
Upon re-reading that thread I find that I may have have Wernicke’s aphasia. Thanks, SD!
So now we’re all clear that the MOAB isn’t a thermobaric weapon, i.e. it doesn’t rely on atmosphere for oxygen to react with its payload.
But we should clear the air, so to speak, regarding thermobaric weapons. They are commonly described as sucking the oxygen out of surrounding air, or sucking air out of nearby enclosed spaces, but that’s not how they work.
The first step is the dispersal of the fuel carried by the thermobaric bomb: a small explosive charge ruptures the tank and disperses the fuel. Once that’s done, the resulting cloud of fuel and air is ignited. The only oxygen that gets consumed is that which has atomized/vaporized fuel in very close proximity to it. IOW, if you’re being deprived of oxygen, it’s because your head is in the fireball, and you’ve got much bigger problems to worry about. If you’re in a cave, and a thermobaric bomb goes off just outside the front door, it’s not going to suck the oxygen out of your cave - but the overpressure event will be problematic for you.
Here’s a lovely slo-mo video of a 2000-pound thermobaric bomb being used against a test house. At 0:09 you see the dispersal event, and at 0:13 you see the ignition. At 0:14 the blast wave hits the house and wrecks it pretty good. But you can see that afterward there is no large-scale movement of air near the house toward the blast center; if the house were a cave, the air would not be sucked out of it. Similarly, oxygen can’t diffuse out of the surrounding atmosphere into an over-rich fireball fast enough or on a long enough length scale to cause significant oxygen deprivation to anyone outside of the fatal blast zone.
Going back to the OP’s bizarre question, there’s video of it exploding. I have no idea why one would think it is a dud.
Could Afghan Forces inspect the caves prior to the dropping of MOAB?
The fact that they can now speaks to the success of the operation.
I think it’s because there’s an expectation on the part of lay persons that it would collapse every cave and obliterate/incinerate everything within a wide area, and the pictures and text in the OP’s article express some surprise that some houses, trees, and caves in the area are still standing. Yes, the video shows it exploding, but few people know how big a fireball they should expect to see from this bomb, so that’s not terribly informative.
Not dud in that it didn’t go boom, but dud in that it was nowhere near as effective as they said it was.