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Crackle - Autoignition


hcb

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I'm new to fireworking. This seems odd, but I don't know much. I thought I'd post this either to learn more (maybe I made a mistake) or to warn others.

 

I was making a 100g batch of crackle today. First batch of crackle ever. Following the recipe given by PyroHook (YouTube, has some very informative videos), I made a batch. The "recipe" is: 37.5g Bismuth Trioxide, 37.5g Copper Oxide black, and 25g MgAl (he used various meshes, I used 200). I used NC lacquer made per his instructions (and several other sources of similar or the same): 16.9g BlueDot (smokeless powder for reloading) to 140ml of acetone.

 

I dry-mixed and screened my dry chems then added the NC lacquer until the thickness of pancake batter (per the video). I then let it begin to dry, stirring in the "skin" on the top periodically. When it was almost ready to form into balls to be processed into 1/8 mesh "micro stars" my son said he was hungry. I put about 3-5cc of acetone on the mix, covered the bowl, and left for about 30 minutes to get lunch with him. When we returned, I stirred the mixture up thoroughly and placed it to dry again. This should have been the final drying before being able to ball it up to roll out and screen cut it.

 

For drying, I was placing the bowl, a shiny stainless steel bowl, outside in the sun. Where I am, it was a warm (about 85) day and full sunshine. This caused the acetone to evaporate quickly. While we were gone for lunch the bowl was left inside in the shade. For the last drying cycle, instead of placing it fully outside, away from the shop, I put it on the concrete floor in the door opening. The door is 12'x12'. The concrete there had hours of sunlight.

 

I went back to work on a piece of equipment in the shop, not near the bowl, and then all hell broke loose. This was within maybe 5 minutes of placing the bowl on the floor in the sun. Like popcorn, slowly at first and then much more rapidly, the mixture began burning and crackling. My son was in the shop, away from the bowl. I was the only other person there and was not near the bowl and not using anything which could produce a spark (and, again, wasn't near the bowl anyway).

 

So, one of a couple of things happened: either the bowl managed to reflect and focus the sun's rays onto a small area of the composition or the composition has a fairly low ignition temperature (less than 200F). Or maybe something else I'm not experienced enough to consider. Maybe I did something stupid by putting it in direct sun to let the acetone evaporate. Or maybe it was stupid to do so in a shiny, reflective metal container.

 

No matter the answer, be advised, this stuff ignited with no external fire/spark source. If it happened to me, it could happen to someone else.

 

--HC

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This is a known issue with stainless bowls. The parabolic shape will focus a larger area of light onto one spot. I've even had crumpled up newspaper laying in the bowl start to smoke.

 

As you are new and doing this with your son, I hope it fully opens your eyes to how quick something can go wrong. Research safe practices and always have a plan. Have a hose or bucket of water close by and it wouldn't hurt to have another with sand. Work far away from any building, wear cotton clothes, and other PPE, and always assume what you are working with could ignite and have a plan. Also, wear a respirator and have your son wear one if working with you. Finely divided chemicals and metals don't play nice with lungs, especially if young and growing. And not those cheap paper masks that barely catch a mosquito, a real respirator that fits.

 

It can sound scary and it can be dangerous. But it's better to be prepared and safe than thinking that nothing can go wrong.

 

Have fun and be safe!

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Remeber to never be hasty, only potassium nitrate and charcoal can be dried in the sun safely and in a certain measure perchlorate composition. Take your time to make any pyro work, this is an hobby and also if is a work calculate the time you need without shortcuts and in excess. I find usefull use plastic and aluminum bowls cheaper and safe.
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As FlaMtnBkr said, it was probably the bowl. Crackle is on the more sensitive side of things I'd say though. I've heard of it happening with strobe composition as well, which is also on the more sensitive side of things. Drying in the shade is still almost as effective as straight sun if there is a breeze so you're aware for the future. I only really allow anything to dry in direct sunlight when finishing something off. This is more for polverone, BP, and pasted shells, etc.

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  • 2 weeks later...

This is a known issue with stainless bowls. The parabolic shape will focus a larger area of light onto one spot. I've even had crumpled up newspaper laying in the bowl start to smoke.

 

As you are new and doing this with your son, I hope it fully opens your eyes to how quick something can go wrong. Research safe practices and always have a plan. Have a hose or bucket of water close by and it wouldn't hurt to have another with sand. Work far away from any building, wear cotton clothes, and other PPE, and always assume what you are working with could ignite and have a plan. Also, wear a respirator and have your son wear one if working with you. Finely divided chemicals and metals don't play nice with lungs, especially if young and growing. And not those cheap paper masks that barely catch a mosquito, a real respirator that fits.

 

It can sound scary and it can be dangerous. But it's better to be prepared and safe than thinking that nothing can go wrong.

 

Have fun and be safe!

Wish I'd known that. :) And that's one of the purposes of having forums like this, to share boo boos so others don't make the same mistakes. Nobody got hurt here, nothing burned to the ground, maybe this will serve to warn someone else.

 

Very much eye-opening. I didn't think this was "safe" as a hobby, but, wow, learned something there. Understood re research and planning on a boo boo. I spent a lot of time reading about crackle and watching a few videos but no mention of this kind of accident. For comparison, searching for info on "flash powder" reveals all kinds of warnings. As such, I've made 10g (small batch, that is...I make BP 200g at a time) of flash powder, wore gear, and had a pucker factor of 7 the whole time. If I'm warned, I heed the warnings.

 

I have 3M 7500 series respirators. I need to get one that will fit my son. I keep him away from the powders while mixing/agitating to keep him out of the cloud of airborne particles, though.

 

I'm only going to do crackle in plastic bowls now. Maybe be patient and skip the "drying in the sun" step.

 

--HC

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As FlaMtnBkr said, it was probably the bowl. Crackle is on the more sensitive side of things I'd say though. I've heard of it happening with strobe composition as well, which is also on the more sensitive side of things. Drying in the shade is still almost as effective as straight sun if there is a breeze so you're aware for the future. I only really allow anything to dry in direct sunlight when finishing something off. This is more for polverone, BP, and pasted shells, etc.

I'll heed that advice re "in the shade" for sure. :)

 

Thank you.

 

--HC

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Boa tarde...

Estou me preparando para fazer esta fórmula pela primeira vez...

Agora vou ficar até mais atento...

Só me falta o trióxido de bismuto.

Não estou conseguindo aqui no Brasil

Será que posso substituir por outro produto??

Ou uma outra fórmula alternativa?

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Google translation of Qhiquinho2 post above:

 

Good afternoon ...
I'm getting ready to make this formula for the first time ...
Now I'm going to be even more attentive ...
I just need bismuth trioxide.
I'm not getting it here in Brazil
Can I replace it with another product ??
Or another alternative formula?

Edited by SeaMonkey
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I was able to duplicate a stainless bowl ignition the first time I tried it. There was a pyro burned so badly he died, and it has been suggested the cause of the accident may have been a stainless steel bowl with pyro in it.

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  • 4 weeks later...

Boa tarde...

Estou me preparando para fazer esta fórmula pela primeira vez...

Agora vou ficar até mais atento...

Só me falta o trióxido de bismuto.

Não estou conseguindo aqui no Brasil

Será que posso substituir por outro produto??

Ou uma outra fórmula alternativa?

Lead tetraoxide (II,IV): https://en.wikipedia.org/wiki/Lead(II,IV)_oxide

 

Lead-Copper Dragons eggs Lead tetraoxide (Minium) 44 Cupric oxide 31 Magnalium (60-200 mesh) 17 Sulphur 4 Potassium nitrate 4

 

 

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Boa tarde...

Estou me preparando para fazer esta fórmula pela primeira vez...

Agora vou ficar até mais atento...

Só me falta o trióxido de bismuto.

Não estou conseguindo aqui no Brasil

Será que posso substituir por outro produto??

Ou uma outra fórmula alternativa?

For those who don't speak Brasilian Portugues:

 

"Good afternoon... I'm getting ready to make this formula for the first time ...

 

Now I'll be even more attentive ...I only lack bismuth trioxide. I'm not getting here in Brazil. Can I replace it with another product ?? Or another alternative formula?"
If you take a look through the threads here and elsewhere (e.g., http://pyro-gear.co.uk/ forums), you'll see that many are testing various crackle/DE alternatives to the now popular but relatively pricey bismuth formulations. If you check out some of member Yus' videos, you'll see several bismuth-free formulas that use barium nitrate, for example, with decent outcomes. USAPyro has a long thread on no-NC DEs that's worth reviewiing. Others are taking different approaches. Overall, the aim is for a low-cost, minimally toxic, no-NC (Chicoms prolly use phenolic resin instead of NC for binding; I'm playing around with that, with good success) but functional DEs and crackle mixes.
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