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Backfire / Shelter Hole Bomb For Firefighters Caught In Wildfire

Drop the backpack, ignite it and run. Then run back and shelter in the hole in the middle of the pre-burned area.
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This backpack incendiary bomb does two things, using thermite, white phosphorus or some other fast burning substance, it burns all the vegetation away within a 3 yard radius, then, using a shaped charge, it also blows a 6 foot hole in the ground.

When it becomes apparent that you're going to be overcome by a wildfire, you drop this, pull the pin and run like hell. The resultant burned area will at least have no fuel once the fire overtakes you and the hole will offer another measure of protection. You put on your fire protection blanket, climb in the hole and have a quick conversation with the deity of your choice until the fire passes, hopefully with you alive to tell the tale.

doctorremulac3, Aug 21 2015

Just hope you don't set it off on top of one of these... Borate_20Bouncing_20Bettys
[normzone, Aug 21 2015]

Looking for shaped charges vs dirt https://www.youtube...watch?v=wdrmCYBPP2g
Not a lot out there, this shows about a 5 inch hole after blowing through some metal plates. [doctorremulac3, Aug 23 2015]


       Will there be enough oxygen left in the cleared area to breathe?
csea, Aug 21 2015

       That wouldn't be a problem, the air would rush right in after the chemicals burned out in a few seconds or so. As the fire burned overhead though, there would not be any breathable air so you'd have to survive on the air in your survival cocoon.   

       Although breathing is certainly an issue, surviving the heat for that critical couple of minutes would be the hardest thing.   

       As far as the hole in the ground, I assume since shaped charges are designed to melt holes in thick tank armor it would make short work of dirt, even with heavy gravel content. I'm also know a shaped charge is good at punching a small hole in that armor but I'm not sure how that would translate to moving a great deal of soft matter such as dirt, but I assume with some tweaking it could be done.
doctorremulac3, Aug 21 2015

       So when the stars are aligned, and one of these devices is set off on top one of the linked devices (link, naturally), then the race between incendiary device and fire prevention device is followed by a shaped charge (technically, ALL charges are shaped, even if only amorphously) going off in a possibly sub-optimal orientation.   

       What could possibly go wrong ?
normzone, Aug 21 2015

       The wildfire that leveled my old man's place reached temperatures that melted his metal shed and the vehicles stored in it.
I'm not sure that a six foot hole and a thermal blankie are gonna do the trick, but (+) for the thought.

       I think what's needed is a reflective thermal cocoon with it's own air supply and a liquid nitrogen canister which is dispensed based on exterior temperature. This should keep the cocoon from melting the way a paper plate full of water won't burn.
Your six foot hole would then come in very handy at keeping exploding trees from squashing you.

       I think the key feature of this is the elimination of all combustible material in the vicinity of the foxhole.   

       Howevertheless, I think it's flawed as written. Rather than using the incendiary to burn the local combustibles (which will include trees and things that can't be burnt away easily), the device should simply be an explosive powerful enough to eject said combustibles from the vicinity.   

       No fancy incendiaries or shaped charges are needed. It's not hard to make a 6-yard-wide crater.   

       A better solution, of course, is to be a firefighter in a place where wildfires don't happen.
MaxwellBuchanan, Aug 21 2015

       // the key feature of this is the elimination of all combustible material in the vicinity of the foxhole//   

       That won't help much. The old man's metal shed wasn't anywhere near the tree-line.
He's got the melted transmission from a Cadillac framed and mounted as art-work.
It's pretty cool. I think of it as the most expensive artwork never purchased.

       Good idea or bad, how fun would it be to do the research to test the concept? Maybe I'll call the Mythbusters guys. They're good at testing things with explosions and fire.   

       Not sure of you'd be better off putting all your explosives into getting that hole as deep as possible. Deep enough and you've got nothing but nice cool ground around you for the duration of the fire only needing to have some kind of heat reflective or evaporative heat dissipating cover on top.
doctorremulac3, Aug 21 2015

       It occurs to me that after the first Iraq war, when all those oil wells were ablaze, they extinguished many of those blazes using explosives. I'm sure [8th of 7] would fully approve of using air-dropped explosives to extinguish the various fires in the Western USA.
Vernon, Aug 22 2015

       If you're carrying that much energy in a back pack why not use it to jet yourself right out of Dodge?
cudgel, Aug 22 2015

       I don't know about a jet pack, those are pretty heavy.   

       A rocket pack however, complete with a parachute might work.   

       Might be able to find a market for a rocket pack/parachute combination for the extreme sports/daredevil market anyway. Anybody ever thought of that? I once suggested a rocket sled that you'd ride up to 5,000 feet or so before you jumped off and parachuted back down. Got a couple of buns.   

       I'm thinking to be practical this thing would have to be 20, 30 pounds or so at the very most. Beyond that you're barely mobile, something that's pretty important when fighting a wildfire.
doctorremulac3, Aug 22 2015

       It won't work. On the other hand, a rocket-powered auger blade, with a final charge in the nose to blow the auger and remaining dirt out of the hole, probably would.
FlyingToaster, Aug 22 2015

       You're adding a lot of weight that isn't explosive. I think you're going to need all the blast you can get. I've used augers before, even in soft mud they need to be wrestled with for quite a while to get a hole going. The one I used was way over 50 pounds as well and it still was a pretty slow process.   

       I'm thinking a ring of shaped charges would do the trick.   

       Let's look at a cross section of the right side of that ring. The blast goes down through the dirt and wants to blow upwards following the past of least resistance. To the right of the right side of the shaped charge ring is solid ground. To the left is a cylinder of loose dirt cut by the ring. The blast is going to want to travel up through this core of loosened dirt since that's where there's the least resistance. As the blast goes down, then up, it carries the dirt plug with it leaving a hole. You could also make it more oval shaped to fit a body with shoulders inside more effectively.   

       The only question is how big the charge would have to be. It's not so much the weight of the explosive, it's the weight of the shaping mechanism which is metal.   

       Wonder if you could rig a rocket propelled grenade to shoot into the ground and blow the dirt out from 5 or 6 feet under the ground.
doctorremulac3, Aug 22 2015

       The concept of a ring of shaped charge is interesting, though arguably it shows up in quite a few "let's break into the bank vault" movies. It would be pretty heavy though.   

       Your underground RPG is going to create a crater, not a hole.
FlyingToaster, Aug 22 2015

       What concerns me is that you have to set up your bomb, run away from it for the requisite distance, wait, then run back. Presumably you were not on fire when you decided to deploy, but were getting desperate; i.e., surrounded by flames. So - you put the bomb in the non- burning area, then run - where? Into the flames, of course - and then back out...   

       How 'bout a bit of a fix. Make this a mortar. Everybody hunkers down, you aim the mortar at a likely looking piece of flaming "I think we can clear that" real estate, fire, hug dirt, wait for the blast, wait for the sky to quit pooping rocks, then run like hell to the crater to pop your shake-and-bakes and dive in.   

       One item that is of importance when getting into fire shelters is the need to get rid of your other gear. Wildland firefighters often carry some very combustible gear - chainsaws for clearing fuel, gas for the chainsaws, fusees for lighting backfires - plus gear that's not welcome in the shelter, such as anything sharp (might poke a hole in the fabric) or metal (conducts heat to the occupant). So the rule of action is: 1) never have your shake-and-bake in your pack, and 2) chuck your pack as far as you can throw it, and 3) don't throw it close to somebody else's shelter (having a gallon can of gasoline go off next to anyone's tent makes a bad experience much much worse).   

       So, if you bomb yonder, you can just divest of pack while waiting for the blast, and run unencumbered to the crater for deploying your shelter.
lurch, Aug 23 2015

       You'd definitely need to dump all your stuff.   

       How about this:   

       1-You've got a quick release that drops everything but the ring shaped charge.   

       2- You run to a suitable location, take this off, and set in on the ground, pull the pin and run away while it blows, then run back and jump in the hole.   

       3- You pull another pin that takes Max's fireproof foam that forms a plug at the top of the hole. You hold it down with a handle underneath.   

       Wonder if you could take the double walled foam filled idea and make a suit out of it. You'd blow up like the Stay Pufft marshmallow man and be fire resistant.   

       Eh, I like the plug idea better. Advantage of a plug is, even if you've got more of a crater than a whole, this plug can be pretty wide and shaped however you want it.   

       Hmm. What's starting out as a "How crazy would it be?" idea is looking more like a "Why the hell not?" idea.
doctorremulac3, Aug 23 2015

       Hmm... Shaped charges are all about making smallish holes in very hard things, so as to get into a pre-existing space beyond. They're not about moving a large volume of dirt out of your way.   

       Moving a large volume of dirt out of your way is what mining explosives do, and they do it by putting the charge underneath the dirt (in a pre-drilled hole), then tamping it down pre-detonation.   

       Just maybe, your shaped charge could do the work of the drill - that is, it could make a deep, narrow hole to drop the main charge into. It'd be a massively fiddly tandem-warhead sort of arrangement, and I'm not sure how you'd get the stemming in place fast enough. Nano-bots with dinky little buckets and spades?   

       Anyhow, I think that might give you a deeper hole with maybe a bit of a lip to it if you were lucky. You could then trade off the reduced heat against the increased danger of being buried alive.
pertinax, Aug 23 2015

       //Hmm... Shaped charges are all about making smallish holes in very hard things//   

       Yea, but I'm thinking if it can cut through 4 inches of steel it can cut through 6 feet of soft dirt. I don't know if that's a correct assumption but if it is, that plug you've cut is just sitting there separated from the ground. When that blast of molten metal loses enough velocity to keep going down, it's going to still have energy to dissipate in the form of a blowback. It will hit the bottom of the hole and want to get back out. Hits the side of the hole, too much mass, can't go there. It then turns towards that loose plug of dirt, goes that direction and carries that dirt plug with it.   


       I'm wondering if stuff like this has been tried for other things like mining and oil exploration. The only reason I see for a relatively small hole made very quickly would be to create places to set charges in. They currently use drills for that, maybe you could save some time by setting a row of 20 shaped charged in a row, blasting them then coming back and sticking your dynamite in. Somebody's had to have thought of that.   

       Back to the dirt hole, I'm wondering if you'd get some benefit from the pressure of the explosion tamping the sides of the hole to some extent to prevent the walls from collapsing. This is a possible side benefit of blasting a hole you wouldn't get from drilling.
doctorremulac3, Aug 23 2015

       Put up a link showing a small shaped charge going through 3 metal plates before digging about a 5 inch or so hole in the ground. The hole seems pretty clean. The charge looks to be pretty small so if you upped the explosive size x 10 and removed the metal plates I wonder if you'd get that 5 foot deep hole.   

       Maybe you don't have a circular ring of shaped charges, just a round array of shaped charges 2 feet wide that digs hundreds of holes together forming one big hole.   

       Another thought, wonder if you're better off digging a trench. You have the charge aimed at a 45 degree angle to the ground so it blasts a neat curved ditch into which you'd lie down. Might be easier to get that mass traveling in a curved line rather than the blast having to make a u- turn.   

       And just occurs to me, instead of thinking of that dirt overhead as a cave in threat, you pull it in over yourself as an insulator. Just make sure it's not so deep you can't dig out. Cut that ditch, lie in it and with a knife, cut away at the walls above you so the dirt falls in over you. Breathing air is somebody else's department, an air canister or something.   

doctorremulac3, Aug 23 2015


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