Wikipedia:Reference desk/Archives/Miscellaneous/2014 November 6

= November 6 =

Are modern tanks resistant to explosive shock waves?
Aside from flying shrapnel, modern conventional explosives can cause bodily injuries via shock waves - differential air pressure that can rapidly compress hollow vesicles in the body. What sort of measures could one take to prevent injuries form these shock waves? Would one have to be inside an airtight chamber such as a pressurized airline fuselage? Do passengers inside a modern tank experience these shock wave pressure injuries? Are modern tanks fully airtight? Acceptable (talk) 01:20, 6 November 2014 (UTC)


 * I don't agree that you want it to be fully airtight. Like during a tornado warning near your house, you want some air flow, to prevent a pressure differential which could cause an implosion.  As long as the air holes are small, the pressure wave will be reduced to a manageable level.  (You might want the tank to be airtight for poison gas, but that's another matter.) StuRat (talk) 01:49, 6 November 2014 (UTC)


 * Modern tanks have an Chemical, Biological, Radiation and Nuclear (CBRN) defence system (it used to be called "NBC"), which as I understand it, pumps air through a filter into the inside, at a greater pressure than the air outside, so that contaminated air won't leak in. I can't find a Wikipedia article about it but I expect that there is one - the article that I linked to only covers civil defence. This forum discusses an M1 Abrams tank that fell into a river in Iraq and the marines inside drowned; opinions by the contributors suggest that a) modern tanks aren't completely airtight (the pressure of the CBRN system isn't enough to keep water out) and b) tanks don't often drive around with all the hatches closed. I found EFFECTS OF NUCLEAR EXPLOSIONS which says that "military vehicles, from jeeps to tanks, are most likely to suffer damage when pushed, overturned, and thrown about by the blast winds."
 * As to tank crews being affected by conventional explosive blast, I imagine not; otherwise huge amounts of effort wouldn't have been directed at attempting to penetrate a tank's armour, you could just let off a big charge nearby instead. One type of anti-tank warhead is called High-explosive squash head (HESH), in which a charge is flattened against the tank's armour immediately before detonation. The shock waves go through the armour plate and knock off a big scab of steel on the inside, which then ricochets around the crew compartment causing all kinds of unpleasantness. However, this is no longer used because modern composite armour, such as Chobham armour, is able to absorb the shock and prevent any damage inside. Alansplodge (talk) 02:36, 6 November 2014 (UTC)


 * The thing about opening windows to equalize pressure during a tornado is bullshit. Matt Deres (talk) 14:08, 6 November 2014 (UTC)


 * That link says the pressure from a tornado is "only" 1.4 PSI. That's over 200 lbs/square foot.  If the side of the house is 20 feet by 50 feet, that makes 1000 square feet.  That gives me 100 tons of force on a wall.  Now walls might be made to withstand that kind of weight, but not that lateral load.  And windows exploding may very well equalize pressure, but the object of opening them is to prevent shattered windows.  I also imagine that sudden release of pressure causes more ear damage than if the windows were open. StuRat (talk) 23:07, 8 November 2014 (UTC)

So in essence, what are the necessary steps one must take to prevent injuries from differential pressure shock waves from conventional explosives? Is hiding behind a concrete blast barrier sufficient? Or will the shock wave go around the barrier and still hit you? Do you need to be enclosed in some sort of structure? Acceptable (talk) 07:24, 6 November 2014 (UTC)


 * I would imagine it would help, but can't find a reference at the moment. In the meantime, I found Blast mines: physics, injury mechanisms and vehicle protection. and Shielding Body Protects Brain From “Shell Shocking” Blast Injuries. Alansplodge (talk) 11:02, 6 November 2014 (UTC)


 * The blast wall would help against fragments, but wouldn't do much for pressure. For that you need an almost completely enclosed structure. 99.53.105.210 (talk) 14:40, 6 November 2014 (UTC)
 * Not so, according to THE EFFECTIVENESS OF BLAST WALLS by Dr Peter Smith, Engineering Systems Dept, Cranfield University, Defence Academy, Shrivenham, UK. which concludes:
 * • A robust, plane, non-deforming wall will reduce peak overpressure and peak impulse significantly in a region extending behind the wall out to between 4 and 6 wall heights
 * • At greater distances behind the wall attenuation of blast wave resultants still occurs but to a diminishing extent
 * • For ‘best’ wall performance the explosion should be at relatively short range from the front of the wall"
 * We have a brief article on the Bremer wall, a type of sectional and moveable wall used by US forces "for blast protection". Alansplodge (talk) 19:13, 6 November 2014 (UTC)
 * I have created a brief stub-article at Blast wall. Feel free to chip in. Alansplodge (talk) 20:32, 6 November 2014 (UTC)


 * Another issue is sympathetic_detonation or cooking off of ammunition and propellant charges INSIDE an armored vehicle by very close, very large external detonations. My younger son, the other members of his infantry squad, the vehicle crew and a medic all died when their M2 Bradley Fighting Vehicle was lured over an Improvised Explosive Device consisting of three 156mm artillery shells wired to detonate by remote trigger, buried in the road they passed over.  The vehicle landed on its back, its exit ports all apparently jammed, and the "combat load" of ammunition for the Bradley's turret gun and other explosives inside the vehicle underwent a sympathetic detonation or cooked off, killing all the men on board. loupgarous (talk) 13:43, 6 November 2014 (UTC)
 * Thanks for sharing your experience; "Lest we forget". Alansplodge (talk) 19:13, 6 November 2014 (UTC)


 * Forgetting the specifics of military technology, let's all recall that shock waves are a very specific thing, and the "the energy of a shock wave dissipates relatively quickly with distance." The exact relation of dissipation with distance depends on the type of shock wave, see explosive velocity and Chapman–Jouguet_condition, and general illustration here . My point is, if an explosion went off near a main battle tank, but the tank was not hit by an anti-tank munition, then (based only off of physical first principles), I don't think the shock wave itself is a very big danger. Tanks are not airtight, but shock waves break apart rather quickly when moving through gaps. Of course precisely how near and the energy of the explosion will matter. SemanticMantis (talk) 22:15, 6 November 2014 (UTC)


 * Or put more succinctly, the unsatisfying to the question in the header is "Yes, certainly." The occupants are in a relatively enclosed space, and will certainly be more protected than if they were outside the tank, at least from the shock wave itself. Quantifying how resistant in terms of protection of human life cannot be done in general. SemanticMantis (talk) 22:18, 6 November 2014 (UTC)