7 replies to this topic

[booom1]

Hi there,

I’m new to the forum (though not completely new to pyro), so hello to you all, and apologies in advance for the lengthy first posting!

I’ve been co-running a small community-based fireworks outfit (Booom!) since 2000, alongside a street-performance company (Miniscule of Sound). I also worked for Walk the Plank in 2001-2.

We’re at the stage of renewing our mortar racks and I’ve been interested to read recently all kinds of things on the net and elsewhere about this subject and was wondering what experience others have had. Although we've always applied strict safety distances to our shows, I don't believe we've ever fully considered the issue of rack failure.

Obviously, there’s been the Kettering incident; EIG have published some tests, as have Pyrogear; and the question even arises in Roy Musk’s public liability insurance form, i.e. “When mortar tubes are in close groups / racks do you allow a gap all around each tube in a bid to avoid misfire explosive force dislodging the next tube and blowing the rack apart?” And: “Have you tested your typical rack to see how it performs under shell misfire / detonation conditions?”

We currently use Imperial Fireworks’ GRP mortars but we’re considering slowly converting to HDPE.

So I’m wondering what the general consensus is regarding: GRP vs. HDPE; construction and testing of racks; and best ways to avoid (those fortunately rare) accidents.

After a particularly gruelling day’s rigging for a show in Scotland at last New Year, I considered the use of a trailer to stack racks in – i.e. rig it all in a covered space and wheel out onto the site in one go. (I subsequently spotted a pic of such a set-up on a US website). But is this a big no-no?

Also, whilst discussing the Kettering incident recently with a fellow pyro enthusiast, he told me that he often sticks a door or such like in front of his racks when he lets stuff off in his (large) garden. Has anyone ever tried using such a blast wall? I was thinking in terms of 3 sheets of 8' x 4' ply lengthways to floor – to create a 24’ x 4’ wall, set up against some kind of a-frame. If a shell was lost through the side of a mortar, it would probably be moving less than 4ft above ground. With the main charge already dissipated through breaking the mortar and rack, the wall might help deflect the remainder of the shell, or at least slow it down, and would certainly deflect any mortar fragments. But I guess for a shell exiting a toppled mortar the wall would be somewhat less effective! Maybe I'm being too hopeful. Perhaps the wall would just collapse. There must be a point though, depending on material used, when this wall would become effective. It would be an interesting experiment!

Lastly (honest!) What’s the best way to destruction-test a rack, as per the EIG/Pyrogear experiments? Is an upside-down shell sufficient?

Many thanks and look forward to discussing further.

Keith
Booom!

Links to some of that stuff:
www.eig.org.uk/eig2002/documents/
www.pyrogear.net
www.theinsurancexperts.com
www.pyrouniverse.com/gallery/displayimage.php?album=10&pos=173

[Caramanos2000]

I have seen these tests, done by a local company. You could try and upside down shell. If you want to take it further, double the break charge in the shell, which should prove the mortars worth, although I would obviously tell you to do this far far away from any shrapnel magnets, otherwise known as people.

[booom1]

I have seen these tests, done by a local company. You could try and upside down shell. If you want to take it further, double the break charge in the shell,

How do that? (I have to say my curiosity hasn't often stretched to dismantling Cat 4!)

which should prove the mortars worth, although I would obviously tell you to do this far far away from any shrapnel magnets, otherwise known as people.

Indeed. I have use of a large field to play in!

[Caramanos2000]

I ment if you made the shells. If they are made by another party, an upside down shell should be fine.

[pyrotrev]

I've been looking at this for a year or two now and done a few (sometimes expensive) tests. Simply inverting a shell is not really sufficient in many cases, because shells differ a lot in their reaction to exploding inside a tube. The overkill way is to test every type of shell you firea couple of times (expensive ), alternatively use a real wicked one - cylinder with stars and salutes that is pretty damn certain to detonate not just flowerpot. Likely you will be somewhat appalled at the results ! But be thankful that you've done it on your own in a large field.

[booom1]

I've been looking at this for a year or two now and done a few (sometimes expensive) tests. Simply inverting a shell is not really sufficient in many cases, because shells differ a lot in their reaction to exploding inside a tube. The overkill way is to test every type of shell you firea couple of times (expensive ), alternatively use a real wicked one - cylinder with stars and salutes that is pretty damn certain to detonate not just flowerpot. Likely you will be somewhat appalled at the results ! But be thankful that you've done it on your own in a large field.

Cheers for that. And once again, I guess you mean sticking it in upside down?

[pyrotrev]

Yes - sorry i didn't make that clear. ANd make sure you have a long fuse/firing cable !

[Arthur Brown]

One of the links you cite suggests that catchers for mis-aimed low trajectory shells exist, and do work, but then suggests that they are probably better for fixed firebases rather than one night shows. As a shell fired from a fallen mortar would take more than casual forces to stop, rather than a shell which had already expended energy leaving a tube through the wall.

I have a personal feeling that the trailer rig could be very helpful in many situations. However would it stand the reaction from a mortar without deflecting? And not everywhere has level vehicle access, to tow it into place.

I actually am looking at the thought of a mini-skip with some sand as a moveable mortar rack with the sand and steel skip to absorb any side bursts. Now re-engineer the miniskip into a wheeled trailer..........