Water, Kevlar, Boom Suppression

OK, another of my general ideas has been kicking around and I’ve not done anything with it. Today, thanks to the explosions in Boston, is likely a reasonable time to “set it free”.

There are “water barriers” that folks might have seen in use. Some are like the concrete barriers that keep cars from crossing to the wrong side of a freeway. Others more like things that keep people away from cars (and have openings in them).

In London, during the IRA bombing years, there were so many bombs in trash cans that a ‘bomb resistant trash can’ was developed.

My idea is a simple one. Make a “water barrier” where the plastic “container” is a fiber reenforced material. Basically, a Kevlar / Aramid like layer thick enough to stop / slow projectiles, that can then be filled with a load of water (that further stops / slows projectiles, but also absorbs and redirects explosive forces.)

There are pictures of some water barriers here:

http://www.unitedsafetyauthority.com/Water_Filled_Barriers.html

They even have an “organization”:

http://www.waterbarriers.org/

Generally speaking, they are used for their very light weight and ease of set up / moving. Then the water is added for mass sufficient to slow / stop vehicles and such. My idea simply extends that to include explosive forces and projectiles.

So instead of a cheap thermoplastic surface, one that is more complex, and strong. Either with embedded reinforcing materials (such as fiberglass or if it works in such constructions, Kevlar) or with a ‘drape’ of Kevlar fabric (on the outer surfaces or in a protected ‘pocket’ inside). In this way, any projectile materials are contained inside the barrier. Also, explosive forces will tend to be redirected up the slope of the walls. The ability of an explosion to do damage to people is strongly reduced when the force is redirected upward toward the sky. Finally, to the extent the barrier is breached, the water spray generated tends to absorb and dissipate the explosive forces. The amount of energy water can absorb is quite high.

So, for example, a trash can made with an inner and outer shell with Kevlar layers, then filled with 4 inches of water, will resist a rather large explosive force and redirect most of that upward though the unrestrained lid. To the extent it gets broken up and sent flying, Kevlar “fluff” and water spray has very high air drag and will rapidly slow below damaging levels.

For “events” like the Boston Marathon, one can set up a line of the “car barrier” kind of these and simply require than any packages, backpacks, bags, trashcans, etc. be behind the barrier. So an 8 foot wide sidewalk viewing area could have 3 feet along the building facade where bags could be placed behind such a barrier, and 5 feet for folks to line up along the street. (As you can’t see much from more than 5 feet back, no big loss ;-)

Now any ‘left package’ can have very limited scope of action. It is either on a person in transit (so they go with it), or behind an energy absorbing barrier where damage is very limited.

At the end of the event, plugs are removed from the barriers and water drains. Now they are “mostly empty” light weight plastic structures that are easily moved and stored. These same barriers can be used for non-threat circumstances (where the Kevlar layers make them a bit heavier, but otherwise the same) and some could be designed such that the ‘drape’ forms could be deployed without Kevlar. (Those with heavier embedded materials will stay heavier).

So that’s the basic idea. Water barriers with a design goal of projectile suppression, explosive force absorption, and force redirection. As long as the top of the ‘package’ area is open, they ought to work rather well. Buildings that are used to fabricate explosives and fireworks have strong walls, but ‘blow off roofs’ for exactly this function. To redirect the forces upward and prevent damage to nearby structures or people. This just makes it all smaller, and lets it be “built on site” with water fill.

If anyone makes these, a footnote of recognition would be appreciated.

Sidebar On Origin

I’d originally conceived of these as a way to give “portable bomb disposal” rigs. A normal bomb disposal trailer has a very large very heavy “tank” on it, where an explosive device can be put inside. My original idea was to make a large Kevlar Ring that could be packed in a patrol car trunk. Then any officer who “sees something suspicious” could just set the ring around it, and hook up the hose to the nearest faucet. (one of those hoses that ‘inflates’ to be included – the ones with a thin rubber liner and fabric shell – along with both a regular hose end and a ‘clamp on’ for bathroom faucets).

I still that has merit too. It would redirect most minor explosions upwards and contain the small debris from most “quart sized devices”. I’d guessed that about a 1 foot thick bag of water would be enough for most things (inside a Kevlar skin…)

A more “stowable” but less effective unit would include an “inflation canister” of Urethane Foam (or similar foam). That way it is just “set the ring around the package, pull the release, and walk away”. It lacks the mass and evaporation heat absorption abilities, but will still do a fair amount of force redirection and projectile trapping. “Beats nothing” by a long shot. Very fast to deploy, and not a lot of ‘time near what goes boom’ for folks not in bomb suits. Frankly, were I an officer in a car, I’d want a Kevlar donut with pull tab I could just put over something and walk away. Makes standing 40 feet from it hollering at folks to “Stay Back” a bit more comfortable… where shrapnel from an unblocked device is ‘line of sight’ for a very long ways…

It would benefit from testing and sizing on a test range.

For high risk areas or where faucets are rare, a 10 gallon or 15 gallon tank of water in the trunk, or even a 20 or 30 gallon canister on a roof rack, becomes an easy and cheap “small town” bomb disposal unit.

So that’s the idea. Hopefully it is helpful to someone. If anyone wants to “hire the inventor” to make it happen, just let me know… There are a few other enhancements I’ve thought of that are a bit complex to put in a posting. (A simple one is a ‘pull tab’ of contact adhesive on the bottom so it ‘stays put’ in wind while inflating and is harder to be pushed out of position by an asymmetrical force. Can also be applied to things on walls then too…)

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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25 Responses to Water, Kevlar, Boom Suppression

  1. Rob L says:

    2 people were murdered in Boston, adding to the roughly 40 murdered on a normal day in the US.

    The only sensible response to this type of incident is to totally ignore it (other than finding perpetrators) and just get on with life. In terms of typical $2-3million cost of life (usual figure for most medical, transportation and other safety based assessments of what it costs to save an extra life) total damage from this bombing amounts to a few 10’s of millions of dollars at typical 2-3 million cost per life + lesser amounts for injuries etc.

    Any significant increase in security efforts, procedures or alterations to barriers or material objects in an attempt to mitigate potential threats will incur absolutely enormous expenses (like TSA) and the money that such changes absorb cost literally 1000’s of lives at that 2-3million per person figure.

    As an example TSA has spent something like $70 billion since 2001 – a sum that if diverted to more useful purposes could have saved 20-30,000 lives equivalent if spent on something like better medicare instead. The TSA effectively killed 10x as many as 9-11 did, and kills more than 9-111 did every year.

  2. R. Shearer says:

    Here in Colorado today, you could pack it with snow. Ice wouldn’t be so good.

    In any case, Rob makes a good point. Far more people will die from driving and texting in the next few hours. If one considers U.S. abortions, on average over 3000 are performed daily.

  3. E.M.Smith says:

    @Rob L:

    And a couple of $200 bits of plastic would have saved not only those three lives, but many of the 100+ injured. Way cheaper than the hospital bills.

    Yes, from a “public health” calculus point of view, the right thing to do is ignore it. From a risk abatement point of view, the right thing to do is to find low cost simple preventative measures.

    Since hiring new “bomb disposal guys” for the one or two who would get killed each year would be cheaper than buying ALL of them those expensive bomb suits, by your logic it’s better to just let them die. Me? I’m buying the nice bomb resistant suit for ’em all.

    @R. Shearer:

    There are many cheap antifreeze systems, not the least of which is just put some salt in the things.

    So if protection is such a bad idea; why do we not have everyone just run out into the snow naked and spend all night freezing to death. That would be even cheaper than building houses and shipping in heating energy… Heck, a cheap funeral is less than a couple of years heating bills for some of those houses…

    Perhaps consider:

    1) There is more to life than the lowest cost path to death.
    2) The purpose of life is to enjoy it, not accept a load of misery.
    3) There are some simple things that mitigate, are not intrusive, and don’t cost much.

    Like seat belts in cars, or having a coat in snowy weather.

    Furthermore, there is the “broken window effect”. If you just let them rack up the body count, you get an escalating body count and escalating rate of bombings. Eradicate the vector and immunize the target. IIRC, the “bomb proof trash cans” in the UK cut deaths by garbage can bombs AND had folks give up on doing it. Long term, significantly less costly compared to decades of IRA bombings…

    I’m showing some simple ways to immunize the target.

    @All:

    I suppose it’s because Dad was a U.S. Combat Engineer. They not only built bridges under fire at the head of the column (W.W.II) but blew them up during retreat as the last guys at the bridge. They got to do laying of land mines, and taking them up again. Oh, and removing various booby traps and improvised explosives. Disarming bombs and such.

    Lets just say I’m a little bit biased in the whole thing to finding simple and easy and cheap ways to protect folks from explosives….

    Oh, BTW, my partial deafness comes from being a bit too close to about a pound of explosives. I’ve had ear surgery to rebuild ear drums. There will be many people from that event having the same. It is the most extreme pain I’ve ever felt…

    So don’t talk to me about it being OK to soak up a few dozen such a year. It isn’t OK. Prevention and mitigation are worth it. Sometimes the spreadsheet is wrong. (Consider that the spreadsheet says it’s cheaper to just slip everyone a bit of poison at retirement… all those old, unproductive, people sucking up all that expensive healthcare, better used keeping folks alive in the 3rd world. In fact, it is so much cheaper per life to save them in the 3rd world, the spreadsheet will say to stop ALL medical care in the industrialized west and ship the doctors, all of them, to 3rd world countries… not a very good solution.)

  4. tckev says:

    I too have thought about the water barrier bomb shield before. One of the modification I toyed with was to make a “Non-Newtonian” liquid/gel for additional protection where needed. Nothing more than adding cornstarch to water and you have it.
    – Reacts like a solid when hit fast (flying water-gel shrapnel), reacts like thick water when hit slow. –
    Cornstarch tend to settle over time but cornstarch with pectin, or better still alginate, tends to stay gelled much longer and reacts better. The ratio of mixes are a bit fussy, it’s been a long time since I thought about it so I’ll have to dig out some old notes (if I still got them).

  5. Such Kevlar bags (though not water-filled) have been trialled for using in aircraft holds, to stop the “few pounds of plastic explosive in the luggage” trick from damaging anything in the plane. Sorry, no links since I saw it on TV around 6 months ago. It certainly seemed effective, and although the other luggage in the bag got somewhat damaged the aircraft had no damage at all from the test.

    These sorts of bomb attacks are very difficult to detect and stop. Probably the worst nightmare for the people tasked with making any public event safe. It’s pretty easy to make an effective explosive in the kitchen (one was chappatti flour and Hydrogen Peroxide, which gives a high-explosive equivalent to C4) and unless we’re willing to accept the disappearance of blonde hair almost impossible to stop. In any case there will be other methods to make explosives, almost as effective.

    What such attacks do to our daily lives is far more disruptive than the few deaths they actually cause. Public events are more expensive because of the security needed, and less enjoyable for the participants when there are people with guns around inspecting all the shopping bags and packages. At the airports, for example, it now takes far longer to get onto a plane, and we are all treated as suspected terrorists with no rights. It costs everyone time and money, and in the meantime makes life less enjoyable.

    The problem with detecting terrorist attacks is that the prevention needs to succeed every time, yet the terrorist only needs to succeed once. These water-filled bags would reduce or eliminate the terrorist’s success, so are a good idea that is worth developing and using.

  6. Bloke down the pub says:

    Bombers such as the IRA choose their target based on it’s vulnerability as well as it’s impact. One of the other measures taken when litter bins were targeted was to replace them with clear plastic bags to make the contents visible. I suspect if every police car was issued with your device the bomber would change target to something that couldn’t readily be contained. It has always been a question of how much society is prepared to be inconvenienced to gain the extra security. You never hear of passengers complaining about security measures before boarding an EL-Al flight.

  7. Gail Combs says:

    Bloke down the pub says:

    Bombers such as the IRA choose their target based on it’s vulnerability as well as it’s impact….
    >>>>>>>>>>>>>>>>>>>
    Given human inventiveness if someone wants to kill they will. There are just too many targets and you can not protect them all.

    Hezbollah Terrorists On Our Southern Border

    Your best bet for limiting damage is to close the darn borders and toss out the illegal immigrants, and the student and H1B visas the Government gives out like candy.

    TSA has cost about $60 billion since its inception. Gov. Rick Perry of Texas, claiming superior experience as the leader of the state with 1,200 miles of the border, advocated a more complex strategy, combining fencing and surveillance technology with “a lot of boots on the ground.” Mr. Perry said that building a border-length fence would take “10 to 15 years and $30 billion” and would not be cost-effective.

    So a border length fence would cost HALF what we have already spent on ‘Grope-N-Fly’ and put people to work.

    Thank you Janet Napolitano for letting all those terrorists in.

  8. punmaster says:

    @E. M. Smith:
    Some very good, and sensible, thinking.

    (Consider that the spreadsheet says it’s cheaper to just slip everyone a bit of poison at retirement…
    For all of the talk about death panels, and the official denials, I am certain this is where we will end up. My neurologist wanted a CT to try to determine why I am having, well, that part isn’t important. Three weeks later, I got a letter from a group called National Imaging Associates which said, basically, ” We don’t believe this is necessary.” Things may not come to the point of poison but they will certainly come to denial of care for anyone even potentially non-productive.

    I need to take the tinfoil hat off as the wife is microwaving lunch and I want to go in the kitchen
    and watch her move.

  9. punmaster says:

    Hmm, I need to go back and read the HTML page again.

  10. Bloke down the pub – as it happens I do complain that I’m searched so thoroughly before boarding a plane. I know I’m not a terrorist, and I want that plane to take off and land safely with me on it. I am pleased, however, that they search everyone else….

  11. Speed says:

    For temporary use, 55 gallon drums filled with water should be sufficient. Stackable if needed. Cheap and easy to move when empty. Fill from a fire hydrant and empty to the street/sidewalk/lawn when done.

  12. Bloke down the pub says:

    I know I risk taking flak with this but it did occur to me that during the IRA campaign of bombing, much of their financial support came from the Irish community in and around Boston. That doesn’t mean that the victims of this weeks attack deserved to be targeted, but then neither did the hundreds of victims of the IRA. Just the most recent example of ‘one man’s terrorist being another man’s freedom fighter’.

  13. Simon Derricutt says:

    Bloke down the pub – also at the risk of being politically incorrect, I could point out that Nelson Mandela never denounced violence in the cause of the ANC.

    I think anyone trying to kill people they don’t know by using the indiscriminate method of bombs or similar should be very slowly and painfully killed – preferably “live” on TV. Barbaric, yes, but it might stop people thinking they were heroes.

    Looking at different countries, I can’t see the ideal freedom existing anywhere, but we can hope for people being treated equally.

  14. Gail Combs says:

    Simon Derricutt, I rather see the coliseum and gladiators make a come back. If some a$$ of a politician or banker wants to promote a war then dump him in the coliseum and let him fight his OWN WAR without involving the rest of us. If the other side does not want to fight, well there are always polar bears.

    My Ex was connected to the Democratic Party and a banking family. He had a Draft number of 3 but some how he missed serving in Vietnam by one week because his papers were ‘lost’ for over a year….

  15. DirkH says:

    ChiefIO, google the guy who bought SegWay and later died falling off a cliff on his Segway.

    He made his fortune with a kind of foldable sack that he intended to be used as portable flood barriers; kinda like a huge sand sack, Turned out that the British Army found a use for them to secure their posts in Afghanistan and bought lots of them and paid handsomely.

  16. Jerry says:

    The person or persons responsible for planting the Boston bombs is simply following in the footsteps of Bill Ayers, Bernardine Dohrn, and Kathy Bondin with an eye out for a future position as a celebrated college professor. Gotta break some eggs to get the street cred don’t you know.

  17. Speed says:

    Bruce Schneier …

    How well this attack succeeds depends much less on what happened in Boston than by our reactions in the coming weeks and months. Terrorism isn’t primarily a crime against people or property. It’s a crime against our minds, using the deaths of innocents and destruction of property as accomplices. When we react from fear, when we change our laws and policies to make our country less open, the terrorists succeed, even if their attacks fail. But when we refuse to be terrorized, when we’re indomitable in the face of terror, the terrorists fail, even if their attacks succeed.

  18. DocMartyn says:

    You cannot use any material that will shatter following an explosion AND has X-Ray properties similar to flesh. Many plastics have these characteristics and this is why they were eliminated from Britain’s cities. Really big bins that can survive a big bomb are fantastic as the blast is directed up. If you can’t have a big safe bin, then no bin is the safest option. It is better to have a dirty city than allow terrorists to place bombs in bins. The England before the Birmingham pub bombings of 74 was clean. After this time, especially in the 80’s, it became messier and messier, as bins disappeared.
    During the IRA bombing campaigns through out my life, I like many English people used to wonder why the Irish Americans of places like Boston were so keen to fund the IRA, via NORAID. We wondered if the people putting money in the hat, for the ’cause’, cared about the human carnage they caused.
    Over and over we have been hearing about the amputees. My eldest brother fits (and designs) artificial legs and has patients who were young people during the bombs in my home city of Birmingham, in 74.

    http://en.wikipedia.org/wiki/Birmingham_pub_bombings

  19. KevinM says:

    The race is 26 miles long. Do you line the whole thing? Do you do it for every marathon? Every sports event?

    Put yourself in the bombers shoes. There are always options. Free sample ice cream day on the Boston common. Earth day in Central Park.

    Like the first guys said, if we’re talking a few dozen victims, keep your government solution out of my libertarian pocket.

  20. E.M.Smith says:

    @KevinM:

    Um, it isn’t a “government solution”. It is a product for anyone. Even a private venue can put in place bomb resistant trash bins and a shielded backpack bin.

    Yes, you protect the entire 26 miles. In fact, since you have trash bins anyway, and since you have personnel barriers anyway, this is just changing the type used, not the existence of them. (Not to mention that the staff cost is the biggest one, not the trash cans and barriers).

    Yes, there are always options for an attacker. But many of them are “not so bright” and will not know all the designs and features of various trash cans and barriers. To quote some cop friends “We catch the stupid ones”. The good thing is that folks who do this kind of stuff tend to the stupid side. So it becomes a percentage game.

    On the ‘donut’ device, it becomes ‘kit’ in the cop car for use wherever someone sees a suspect device. Unless you think folks will never be seeing “suspicious packages”, it is of benefit. Doesn’t matter what event or what place.

    We have an existence proof that raising the protection levels works. Israel was having the “bomb a week plan” some years back. They implemented procedures and devices and bombings dropped way off. This isn’t a “no win” game.

    Basically, “bad guys” like easy targets and Name targets. By hardening the easy targets and the Name targets, more of the bad guys give up, or get caught trying to take on a hard target.

    That’s how, essentially, all of protection works.

    The argument for “doing nothing” amounts to an argument for no locks on doors of houses, no keys needed for cars, and no anti-virus software on your computer. After all, none of them solves 100% of the problem. Yet we do those things because they do solve enough of the problems (and catch enough of the bad guys) to make it valuable. Yes, burglaries still happen, cars are still stolen, and some viruses still make the rounds. But fewer of them, and with higher risks fo the bad guys of getting caught.

    Preferably at the lowest cost and highest effectiveness possible. IMHO, these devices deliver a lot of improvement in safety, and increase in difficulty for the ‘bad guy’, with minimal added cost.

    If I ran, say, a private sporting venue, I’d be looking for a product that makes trash cans bomb proof. I’m already spending a bunch of money on the trash cans, and one that is about the same cost, but reduces risks, and discourages attackers from taking that approach, is the one I’d buy.

    Doesn’t stop the guy from parking a car bomb in the parking lot, but keeps it outside and with lower population density. That’s a net gain.

    To quote one of my favorite movies: “Never give up. Never surrender!”

    Maybe it’s because when I was “Dir. of Facilities” I also had physical security as one of my jobs. I’ve also spent decades doing computer security. I’ve had to plan security for events, and do things like security sweeps. (At a private company, BTW…) I’d like to have this product available for just that job I had to do then. Having a “bag area” with a bomb resistant perimeter, that’s as cheap and easy to set up as one with metal barricades? Easy decision to say yes. I’m going to be renting barricades anyway, and paying for the set up. Just not a problem, and no, or nearly no, added cost.

    @Doc Martyn:

    The plastic can be doped with metal ions to show up on X-rays, and to the extent it works, there will be a lot LESS “stuff” flying around. The inner layer gets shredded, but it then hits the water layer and slows a lot, then gets caught in the Kevlar ‘catcher’ layer. Like ballistic armor, where the shirt fibers get caught in the vest material.

    BTW, doped plastic is used to make gun parts that show up on X-ray machines. Not a new tech.

    I’m proposing a different approach from “more mass” in having “energy dissipating water” and “fragment catching” wrapper.

    @Speed:

    And part of refusing to surrender and refusing to be terrorized is mitigating and thwarting future attacks. To meet force with counter force and counter actions.

    @The IRA Thread:

    Curious symmetry…

    Perhaps there is Karma in the world…

  21. KevinM says:

    All well and good if I’m not paying for it.

    I’m not advocating “do nothing” and I would not stand in the way of someone else buying that protection for themselves or others.

    I do not think Israel is go good example of the trade offs between free and safe. The tri- culture obsession with that exact geographic location is absurd. All of the wasted lives and resources spent capturing and defending territory there could have built an equally sized secure nation somewhere else.

    Locks, car keys and antivirus software are all personal choices. All three examples are included by their manufacturers. And not everyone uses them all the time, or believes they would deter a determined thief or hacker.

  22. Speed says:

    E.M. Smith wrote, “To meet force with counter force and counter actions.”

    At an appropriate scale. Strengthen and lock cockpit doors but don’t pat down each and every passenger or prohibit four ounce containers of shampoo in carry-ons.

  23. DirkH says:

    KevinM says:
    17 April 2013 at 11:21 am
    “I do not think Israel is go good example of the trade offs between free and safe. The tri- culture obsession with that exact geographic location is absurd.”

    The Zionist movement was looking at other places. They wanted a Jewish state, SOMEWHERE. Uganda was considered, for instance.
    Later they were able to strike a deal with the British Empire and were able to settle in what would become Israel.
    Don’t forget that Zionism was basically an atheist socialist movement.

  24. Graeme No.3 says:

    It would be difficult to dope Kevlar with metal, but easy to dope the surrounding ‘plastic’ for UV.
    There has been a good deal of work on fracture in plastics. Starting with impact resisting types like LDPE, polycarbonate and CR39. The latter two are transparent, esp. the last as used in safety spectacles etc. but rather costly.
    Composite ‘plastics’ where Kevlar is used in some layers, and other layers act as absorbers are the usual approach. Things like fillers and ‘rubbers’ which disrupt fracture waves.
    Putting water into the bin would help as it could disrupt some firing mechanisms and also spread the shock waves to more equal pressure on container walls.

  25. E.M.Smith says:

    As an example of putting metal on Kevlar:

    http://www.freepatentsonline.com/5151224.html

    T. Inabe, et al., in Polymer Materials Science Engineering, Vol. 49, pp. 89-93 (1983) disclose electroconducting polymers of polyamides (aramides) and metal phthalocyanines.

    T. Inabe et al., in Synthetic Metals, Vol. 9 pp. 303-316 91984 (1984) disclose the preparation of environmentally stable, flexible, oriented electrically conductive fibers. Solutions of phthalocyanine containing macromolecular, [Si(Pc)O]n, or molecular, NiPc, a metal precursor and a host polymer, “KEVLAR®”, a trademark of the DuPont Company of Wilmington, Delaware for an aromatic polyamide fiber of extremely high tensile strength are wet spun to yield, after halogen or electrochemical doping, strong, air-stable fibers with thermally activated electronic conductivities as high as 51/4-1 cm-1.

    None of the above references individually or collectively disclose or suggest the present invention of simultaneously producing a metal phthalocyanine doped conducting polymer of poly(dithiophene). The present invention is very useful to provide an electrically conductive polymer based on dithiophene having a metal phthalocyanine as a dopant.

    So it’s not that hard to put a metal doped skin on an aramid fiber… I’d expect the kevlar layers to hold up to most IED sized explosions anyway (if the thing is designed right at all) and catch / retain most of the projectiles. But if it is a concern, with a bit of coating, the fibers can be made to conduct electricity and / or show up on x-rays.

    FWIW, a technique of reenforcing brick masonry has a fiber skin layer put on it. Think super thin layer of fiberglass. It still ends up looking like brick (the stuff is transparent / translucent) and there is a similar coating for glass windows that’s a clear polymer sheet. In major quakes they can prevent breakage. In great quakes, things break, but you don’t have fragments flying as they are stuck to the membrane.

    The idea here is similar. A reinforcing / catching layer, and a structural layer, with mass / water in between to cool hot gasses, dissipate the energy, slow projectiles, etc. etc. It’s a variation on the layered armor approaches and water filled crash barriers kind of combined… The inner layer might well break up, but the water holds in place for the duration of an explosion (inertia is your friend ;-), redirecting a lot of the force upward, out the open ‘side’. What force is applied to the inner layer, accelerating it, and whatever shrapnel hits the inner layer gets dissipated into the water layer; then all of it runs into the Kevlar Catcher. Anything that ends up getting through all that ought to be going at modest enough speeds to dramatically reduce blast damage range and degree of injury.

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