13 replies to this topic

[PyroCreationZ]

Ok, I just had an accident in my garage... Luckely a small one and I'm only slightly injured.

Here's the story:

When I buy ematches they don't come with pyrogen so I have to dip them myself.
To do so, I need a sensitive composition (obviously ) and NC as a protective coating (think you all know).
As I don't have commercial NC laquer I make it myself from pingpong balls. This works just as good.
Doing this manually takes some time. So, to make life easier, I use a (coffee)grinder.
I've done this a couple times in the past without any probs until now.

I was busy grinding the ping pongs one by one when all of a sudden I saw a (yellow) flame inside the (hard) plastic container.
Immediatly I heard a sizzling noise and saw brown smoke inside the container. I was about to open the container but realized it was about to explode because of the pressure building up inside.
I was very lucky to turn away my head just in time when it did explode.
Because it was inside the garage (door open though) this strenghtened the sound.
My ears were buzzing for a few minutes and some time later I saw blood on my hand. There are a few cuts from the plastic shrapnel but not too serious.
If I had turned away my head a few seconds later I could've been blind by now

As for the container... plastic shrapnel must be spreaded all over my garage as I could find very little.

Below are pics from my hand and the grinder with container. Or what's left of it...


(click image for larger view)


(click image for larger view)

There are probably 3 possibilities:

- Small metal particles from the workbench got onto the ping pong balls causing a spark in the container wich then would ignite the NC dust.
- Friction causing heat and igniting the NC.
- Motor contamination that got into the container through the bearing.

Let this be a lesson to all of us: if you make NC yourself with ping pong balls, cut them by hand!
I know I will ...

Edited by PyroCreationZ, 27 August 2010 - 07:08 PM.

[PyroSkitz]

Holy moly...thats something i wouldnt expect to cause an accident ??, what was the cause for this by the way ? did you work it out ? + glad you only suffered minor injuries and hope you recover ASAP

[crystal palace fireworks]

Glad your OK, perhaps its time to either consider wearing full face protection, or grind remotely outside under shelter with blast shield/mirrors.

[pyrotrev]

I've always been worried by the potential for explosion of coffee grinders (and ball mills for that matter) with screw on lids. Removing the locking tabs and holding the lid on with some strong rubber bands ought to be much safer.

[vaslop2005]

I always feel very nervous having to be that close to something whilst its being ground... so i usualy wrap my blender in a teatowel (probably in a vain attempt) to try and reduce any effects of a fire/explosion from inside.

I am quite surprised that such a small amount of NC (as you cant fit much in a blender) and of such a weak form, could cause that to explode. I'll definitely be more carefull from now on...

[MDH]

I find it more ironic that they make ping pong balls out of something which is sensitive to shock.

[PyroCreationZ]

Thanks for the friendly comments.

I haven't (and probably never will) found the cause of this but again I can only suspect one of the reasons mentioned in the first post.
I would wear face protection whenever I'm making flash/salutes etc. but I (and probably most others) never expected this to happen with grinding some "innocent" ping pong balls.
As for the cuts, they stain alot but they'll heal soon

Wrapping your blender in a towel won't help much I suspect. The plastic shrapnel is like a small granade and could pierce it.
I had something made out of plastic nearby and now it's full of holes so...

I'm also very surprised that such small amount NC (there was only 1 ping pong ball in the grinder) could cause that much trouble.
Looks like it was enough to build pressure inside causing it to explode (loud and hard!)

It all happened so fast... I had barely any time to respond.
Then again, I'm thankfull I got warned by the flame and heard the sizzling else I probably woudn't be looking at my screen with both eyes...

I've noticed some shrapnel also hit my fingernail and I'm sure I'm going to feel that a couple days.. auwch!

Grinder? No thanks

Edited by PyroCreationZ, 27 August 2010 - 10:15 PM.

[PyroSkitz]

ohhh, i get it now , you had actually mixed acetone and ping pong balls in a blender ??, i was thinking just ping pong balls and you where making them into smaller pieces so they would dissolve quicker...
and yeh nitrocellulose can detonate right ? i am completely a newb to this topic so please correct me if that's untrue hah , im guessing for saftey get a mild steel box made for your bullet bledner hha...i guess one could be made for a ball mill under similar circumstances using mild steel... if you stop the lead balls at the start they wont gain enough momentum to become dangerous ??

[cooperman435]

Im sure he was grinding the balls on their own to make them smaller not with acetone as I can say from experience acetone and bullet blender bases dont mix (well they do but not well in the good sense)

A container around the unit, blender or ball mill would probably in my opinion do little to help as the expanding gasses would throw it all away as extra material and not stop when it hit it anyway, containment is not the idea but delection away from a certain safety area is.

Glad your ok anyway mate.

Phill

[RFD]

Its surprising how something seemingly innocent can have such a potential hazard to it,ive ground charcoal in a coffee grinder quite regularly but always make sure the motors not starting to overheat,ive seen info on grinding oxidizers in them,definitely not for me sounds like a recipe for a trip to A+E,perhaps squashing the pingpong balls,cutting them up and putting straight into a pot of solvent might be a bit safer.

[crystal palace fireworks]

If anyone saw the `Home Movie Roadshow` program on BBC2 yesterday, you will notice the potential dangers with NC and old film reels.

[PyroCreationZ]

As Phill said (spoke with him immediatly after the accident) I was grinding them separatly, no acetone involved. Besides it would be a messy job & wouldn't mix well.
Dissolved pingpong balls are like thick (sticky) paint.

A container around the blender or a ballmill might help slowing down the shrapnel a bit yeah but then again, it would also mean more (deadly) shrapnel flying around.

Just like RDF, I've also read about grinding chems seperatly in a coffeegrinder (skylighter's newsletter if I'm correct) but I wouldn't (dare) try this. The high speed rotation of the blades is way too dangerous imo (heat, lots of friction, etc).
I wouldn't use anything else but a ballmill. Might take a bit more time but still better then putting yourself in danger.

It sure is possible to operate a grinder remotly but how many of us would actually do that?
Also, grinders aren't designed to rotate for a long time, that's why most of them are "push to operate".
A ballmill is something else, I always use an extention cord and a timer. 1 because it's safer and 2 I know exactly how long my comp has been milled.

squashing the pingpong balls,cutting them up and putting straight into a pot of solvent might be a bit safer

I agree. Best thing to do is squash, cut them and put in lots of solvent in an air tight container (make sure the container doesn't melt from the acetone )

Edited by PyroCreationZ, 28 August 2010 - 08:12 PM.

[Vic]

Glad to here your OK PyroCreationZ

Just to add another word of caution when using coffee grinders.

Used mine just for charcoal, it was of the type that has a push button on top that goes down to the motor switch.
I was never very happy about this argument so I decided to strip it down and have a look.

The whole of motor and casing were covered with charcoal not only had it been leaking down past the switch rod
but also around the stainless steel bowl as well!
Never used it again.

[PyroCreationZ]

Glad to here your OK PyroCreationZ

Just to add another word of caution when using coffee grinders.

Used mine just for charcoal, it was of the type that has a push button on top that goes down to the motor switch.
I was never very happy about this argument so I decided to strip it down and have a look.

The whole of motor and casing were covered with charcoal not only had it been leaking down past the switch rod
but also around the stainless steel bowl as well!
Never used it again.

Thanks fflach.
I think that might as well be the same problem I ran into. Not sure though.

BTW: I found the container and by my surprise it was not blown into smithereens.
Seems that the plastic thread broke and launched the container upwards like a rocket (lol? ).
Only a few plastic fragments from the bottom seem to have hit my hand.
Still, I feel 'lucky' not to be hurt more badly but that doesn't change my mind on using such grinder ever again for pyro purpose.

Edited by PyroCreationZ, 04 September 2010 - 08:27 PM.