Sciencemadness Discussion Board

Construction of a blast box

German - 13-5-2009 at 01:33

The vast majority of my reactions I am comfortable with just my lab goggles and apron but there are a couple reactions that I would feel much more comfortable doing inside what I would call a blast box. This would be a box appx 2ftx2ftx2ft that would be something like steel or kevlar on all sides and then on one side would be like blast shield glass or whatever clear strong blast resistant material there is. Then the top could be quickly opened and securely shut. The only opening when shut would be tubing coming from the inside to vent gas (and maybe tubing going in to fan air in). Does anybody have any ideas on how one would construct such a box, or better yet where I could buy something similar (I don't need a huge massive fume hood who's purpose is mostly just about fumes, my main concern is completely containing a blast).

German - 13-5-2009 at 01:39

I'm thinking getting 6 2ftx2ft sections of something strong and durable and clear and then putting them together with a very strong epoxy/resin and then the top one screwing in with latches so I could open and close quickly. Then I'd screw some holes in for the vent tubes. Any ideas on the material that I want?

bfesser - 13-5-2009 at 06:38

Leave the top loose, like an old shoe box. That way, if there is an explosion, the blast energy is directed upward, rather than building up pressure resulting in failure of the containment and shrapnel.

watson.fawkes - 13-5-2009 at 06:51

Quote: Originally posted by German  
This would be a box appx 2ftx2ftx2ft that would be something like steel or kevlar on all sides and then on one side would be like blast shield glass or whatever clear strong blast resistant material there is. Then the top could be quickly opened and securely shut.
I can't say I'm an expert on this, but you can't contain a blast by making a bigger bomb without using an awful lot of mass. (Got a spare underground bunker and remotely-operated robots?) If there's a blast, you've got a lot of sudden gas to deal with. The correct answer is not to put all that gas in a sealed box. That sealed box just becomes a bomb.

Containing a blast means directing the direction of blast energy. It's more like constraining it in phase space than it is containing it with a barrier. You're trying to keep the directions of motion (gas, shrapnel) away from valuables, principally you, secondarily other equipment.

As for design, it matter just how energetic your reaction is. Is it an explosive, or is it simple overpressure on glass?

German - 13-5-2009 at 12:32

It's for the release of hydrogen during an exothermic reaction so if something would happen yes it would be an explosion.

Here's what I'm thinking. Go to a metal shop and have them construct me a steel 5 sided box all melded together. But the top would be able to flap open and latch closed tightly, and the front missing a side would have two sleeves running up and down the two sides where I could slide in a piece of blast glass/plastic. I'd have two holes screwed where the venting tubing would go in and out and in the back section I would have a flap that is airtight but could give away in a blast. My blast energy would be directed through that flap. Metal working is pretty cheap so that I think would be a cheap self-made blast box. I still don't know what would be the best and strongest clear material for the front side though. I think it's some kind of plastic.

watson.fawkes - 13-5-2009 at 17:32

Quote: Originally posted by German  
[...] in the back section I would have a flap that is airtight but could give away in a blast. My blast energy would be directed through that flap.
Why not just make your sacrificial panel out of aluminum foil and cardboard, or something equally flimsy? Consider it an expendable, rather than a durable part of the equipment.

Regardless, you should make sure that the sturdy parts of the cabinet are affixed to sufficient mass that the whole box doesn't move in the case of an explosion.

Oh, one other thing. If you're going to homebrew a piece of life-safety equipment like this, make sure to test it (more than once) before you put it into service.

Arrhenius - 14-5-2009 at 19:54

Most folks wouldn't use a blast shield in the type of reaction you described, which I assume is your borohydride reduction. I'm all for being cautious though.

The common blast shield found in synthesis labs is a curved piece of thick plexiglas (maybe 3/8") with a very heavy weight at the bottom. This is sufficient for bench scale reactions, but not multi mole scale.

I've had hydrogen combust in a 1L flask (open to air), and it didn't explode. If I recall, hydrogen actually implodes.

[Edited on 15-5-2009 by Arrhenius]

grndpndr - 15-5-2009 at 06:41

This idea is just a suggestion as to how large scale munitions storage reinforced concrete storage bunkers were designed at the abandoned storage facility out here.As some have suggested the top of the concrete bunkers were sacrificial should a major detonation occur.The half circle 'Igloos'were all very substantailly built other than the tops which were sacrificial being but a few inches thick with a foot or 2 of earth on top.Intended of course for the top of a large scale blast container to be sacrificial in cases of dramatic failures.the blast would remove the tops of the blast directing them skyward therby protecting nieghboring igloos which apparently they were succesful at as there are several missing igloos due to accidents with intact igloos next door.They also incorporated a small,to this scale thick steel vent actually an Ideal size for what you propose.But in this case to hopefully reduce blast effects of smaller dets such as single Rifle grenades or a mortar round to vent rather than cause a sympathetic detonation of remaining he.But these munitions bunkers have the floor space of about 1.5 size larger than a tennis court.:o

Ideal test site for largers devices if access wasnt such a pain in the ass these days.Strangely enough the gov. still keeps title to some half dozen or more of among many hundreds of Identical ww2 facilty buildings and base to support it.Love to know just what the gov has stored there abouts?:D

The facility was in fact so large the majority of the workforce among the miunitions was civilians and POWs

Still id use some of those design criteria such as a vent for smaller expolosions and a intentionally weaker top or rear
likely with added protection outside the weak side of the blast box.What I used for the box material would depend on materials I could afford and have access to .thick plexiglass of course to enable witnessiing of the blast in safety.The rest of the box could even be built of a plywood material perhaps 2 layers of 3/4 in ply using good carpentry design /practice and assembly with screws and e-poxy a small rear vent as well as the weak link incorporated so if it should fail fragments could be directed in a 'safe' prepped area.Of course if you had access to scrap steel and a welder a more sophisticated /stronger approach could be attempted but the safety aspect would have to be even better thought out. Im contemplating a much simpler design for protection when pressing caps,still potentially dangerous but perhaps not near what you envision?Noise would then be you biggest enemy if you had nearby neibors who didnt know you well and would automatically call authoritys.In thehe event it was shoddily consructed it might not matter to you in any event.:(

[Edited on 15-5-2009 by grndpndr]

[Edited on 15-5-2009 by grndpndr]

zed - 15-5-2009 at 19:11

watson.fawkes is correct. You are building a bomb, not a safety device.

The attempted containment of a potentially explosive gas mixture, is a bad idea. In fact, fizzles, and flashes..... become explosions if you try to contain them.

Vent the Hydrogen via a fan/blower, or perform the reaction outside.

A small uncontained hydrogen fire might be a bad thing. But, the detonation of a 2ftx2ftx2ft cube, containing a mixture of 2moles of H2 to 1moles O2..............

Oh man.

grndpndr - 16-5-2009 at 04:17

Id have to admit they are correct,attemting to construct a device to contain an explosion is asking for personal injury/ death or incarceration.Trying the same inside one of our igloos on the same scale using a remote viewing camera would be safe. I would assume.Less would/could be disaster.
I seriously misunderstood your intent!:(

[Edited on 16-5-2009 by grndpndr]

Contrabasso - 25-7-2009 at 02:17

Better to create a shield to protect you from debris and blast but small enough NOT to constrain the reaction.

Better still to find a way to redesign the reaction vessel so that the evolved hydrogen is safely removed from the reaction site. Flare it off elsewhere after passing it through a flame check valve or dreschel bottle of water.

MagicJigPipe - 25-7-2009 at 05:52

You should at least use some type of "bullet proof" or (shatter resistant) polycarbonate/glass for your viewing window. It's a little expensive but not very hard to find and work with.

You should be able to cut it with a table saw (with a blade that makes sense). Keep in mind that that kind of "glass" is very thick. I can only assume that a diamond "coated" blade would work best (and last longer). This is what we used at Lenscrafters to cut a rough pair of curves in polycarbonate (and glass) lens blanks.

The cool thing about polycarbonate, and many types of "bullet proof glass", is that they are easy to drill, making short work of attaching it to a box of some sort.

And of course, always make it at least 10x stronger than you think you will need and, as mentioned above, do not create a larger metallic bomb by not creating any weak areas in the box (analogous to a burst disc in a CO2 tank) that are directed towards a "safe area" (like a very dense but soft disposable object).

Good luck and be careful...





watson.fawkes - 25-7-2009 at 10:14

Quote: Originally posted by MagicJigPipe  
You should at least use some type of "bullet proof" or (shatter resistant) polycarbonate/glass for your viewing window. It's a little expensive but not very hard to find and work with.

You should be able to cut it with a table saw (with a blade that makes sense). Keep in mind that that kind of "glass" is very thick. I can only assume that a diamond "coated" blade would work best (and last longer). This is what we used at Lenscrafters to cut a rough pair of curves in polycarbonate (and glass) lens blanks.
Polycarbonate can be worked with any woodworking tool, including ordinary table saw blades. While tough, it's fairly soft and easy on tooling. The only real precaution is to make your feed rate fast enough so that you don't start melting the plastic because of friction. All the same goes for acrylic and other plastics as well. You only need to worry about tooling material and composition when you are working plastics with abrasive fillers (at least for common plastics).

Hexavalent - 24-3-2012 at 11:26

Sorry to bring up an old thread, but I recently made an explosion shield by securing an 8mm piece of acrylic to a large piece of coated wood, using very heavy shelving brackets. It's great, and I always use it when performing vacuum operations lest the glassware implode and spray glass shards and lab chemicals all over me. . . .

Endimion17 - 25-3-2012 at 05:22

The idea of making a blast box by making all the sides blast resistant is fucking stupid. Sorry, but if you came up with such idea, you shouldn't be experimenting with explosives. That's a recipe for disaster.

If air humidity is a problem, make a metal frame with the front panel (facing you) made of blast resistant glass, and the other sides made of clear plastic bags, and put a dessicant bag inside. If something detonates inside, nothing can reach you, and the other sides serve as a cushion which will come off in case the volume of the liberated gasses is too large. If you work with reasonable amounts of materials, that will never happen.

Be sure to electrically ground your box because such box can experience a charge buildup. Not only things like aluminium powder will cling to the sides and mess it up, but any spark in a dry environment filled with explosive powder could trigger an explosion.

I'd ground it by taping numerous straight copper wires (spaced 1 cm apart) to the baggy sides and connecting them to the wire that's soldered onto the metal frame, and then connect the main wire to a water pipe. It might not be enough, but that's the first thing that comes to my mind.



edit: crap, this is an old thread. oh well. :D

[Edited on 25-3-2012 by Endimion17]

phlogiston - 25-3-2012 at 05:38

As a cheaper alternative to bullet proof glass, perhaps you could view the reaction through a mirror.

A good setup IMO would be a single thick sheet of metal, perhaps slightly curved around the area you want to shield. The sheet should be firmly fixed at the top and bottom. Then, a mirror made of something that won't produce too much shrapnell (but there will be some from your glassware anyway) positioned so that you can view the reaction from the side/behind.
It would also be very useful if the blast sheet was able to slide away, like a window, so you can work on your setup without obstruction.

The back of the fume hood should absorb shrapnell. Perhaps a layer of foam on a sheet of wood?

[Edited on 25-3-2012 by phlogiston]

Ozone - 25-3-2012 at 08:44

"You are building a bomb, not a safety device"

Enough said.

A box with permeable fabric (e.g. Kevlar) walls and loose top might be ok. I think what you are looking for is a "blast shield" not a "blast box". They do sell these, I have two--1" lexan curved and mounted to a polymer coated lead base. Fortunately, I've never tested it (e.g. with an explosion).

O3

Hexavalent - 25-3-2012 at 09:58

We use similar shields to them at school . . .the teacher demonstrated a thermite reaction behind one that actually broke his crucible, sending bits of hot porcelain everywhere . . .saved him and the class from a nasty surprise:)

TheChemINC - 25-3-2012 at 13:18

in fireworks factories, they will have building with very stong walls and roofs that are barely held on in case of an explosion. that way the blast is directed upwards. i know that something like this was said earlier, but i fel the need to add my two cents :P