Strange Accident (Almost maiming)

[MeowMix]

I was simply making some Sugar/KNo3 smoke mix. I was making a larger batch than normal, about 400 grams. When melting the sugar and kno3 mix on my hotplate, is very randomly burst out in flames. And since it did not have a nozzle and simply in a pot, a large flame shot straight up barely missing my face. Burnt my nose pretty bad and some of my hair. If I was leaning slightly forward it could've easily hit my eyes and more of my face. Luckily I was relativity un-injured. I do have a large blister on my hand though (the one that was holding the spoon). It shot hot piles of comp all over my workplace and sadly staining my table with burn marks. Also filled my shed with smoke, obviously. It didn't start any fires or worse, but I was very surprised when a pretty harmless comp burst out in flames. I'm really not sure what caused it, as I was outside with no source of ignition other than the hotplate, which was at a pretty low temp. Either way, it was quite the experience.

[Andres1511]

The temperature control mechanism could be broken, that happens fairly often with cheap hotplates. Bad stirring due to the larger batch could have lead to over heating and the ignition. If you're hotplate is some good quality brand or if you're sure you were stirring really good, I don't know...

 

There is so much that could have happenned.

Good to hear your injuries aren't that bad.

 

Quick recovery man.

[mikeee]

You might want to wear a face shield when you have that amount of comp on a hot plate.

It is only a matter of time before these accidents happen, not if it happens, but when it happens.

Even a set of googles and a filter mask would reduce the exposure to a fireball.

[PhoenixRising]

.

Edited June 27, 2016 by PhoenixRising

[dagabu]

Im glad you are OK (for the most part) and I'll just repeat what thew others said, PPE and keep stirring!!

[Arthur]

We wouldn't be interested if it was SAFE! However once you realise that there are hazards, then you must learn to recognise the hazards and minimise them, then mitigate the remaining hazards by use of suitable PPE Every mixture has hazards as does every method. Appreciating these hazards and their risk really is your job.

[stix]

Yeah, good to see that you're ok. I wonder if one of those IR thermometers might be handy to check the temp periodically?

[Arthur]

The problem with attempting measurements with a semi solid is that the heat and temperature distribution through the mass will be very variable. Lots of it could be at 100C but just a small piece could be at 250C and just about to thermally run away.

[stix]

Yeah true Arthur, but how would the mix be at 250C? Sugar melts at around 186C - I guess that center ring can get hotter if you're using a standard electric frypan/skillet but that should already be taken into consideration.

 

After a thorough mix of your KNO3/Sugar, a quick check with an IR thermometer could alert you to a possible malfunction of the thermostat. Although the smell of caramelisation would normally be a good indication.

 

I do wonder what exact methods MeowMix was using:

 

. . . And since it did not have a nozzle and simply in a pot, a large flame shot straight up barely missing my face . . .

 

Can you please explain what you were doing. Your near miss may help others and yourself avoid something similar or worse. Don't worry about if you made a mistake so long as it's learned from.

 

Also, I don't think that it's necessary to melt the KNO3 and Sugar together. I haven't made any but from what I've read, http://styropyro.com/tutorials/smokebomb.htm a simple dry mix added to melted wax makes a perfectly serviceable smoke bomb. 60-70C to melt the wax - which is done safely and separate, and the dry ingredients are mixed in.

[dagabu]

I took a peek at my fry pan and I see that the temp probe is part of the plug assembly and not part of the pan. The element is in no way being controlled at the pan surface and there is no way short of taping a thermocouple to the pan bottom, to tell what the temp is at the surface, including an IR thermometer.

[otto]

I had an encounter similar to this sometime ago, like the mid 60s or thereabouts. Had one of those retail chem sets. Of course the pamphlet experiments were "boring" so we threw that away and had at it.

 

I remember putting some KNO3 into a test tube and heating it over something (probably a candle). After it melted I went to stir it with one of those wooden sticks that came with the kit and it immediately burst into flame shattering the tube. Most of the contents were consumed in the reaction. I never forgot that. I was only 10 years or so but I surmised that the oxidizer heated past a critical point would instantly react with an introduced fuel. Still don't know if that's entirely accurate but I suspect someone here might have an observation on that.

 

Is it possible a critical temp was exceeded and a mishap ensued? I've still got a lot to learn but this thread did jog a memory.....

[stix]

I took a peek at my fry pan and I see that the temp probe is part of the plug assembly and not part of the pan. The element is in no way being controlled at the pan surface and there is no way short of taping a thermocouple to the pan bottom, to tell what the temp is at the surface, including an IR thermometer.

 

Same thing on my pan Dave. I did toy with the idea of attaching a thermocouple and controller but went off it because I'm using an oil filled one and there would be way too much lag to be effective.

 

What I did do though was to verify the temp using an IR thermometer - the fuel I use has a small amount of carbon black which makes it look almost black, so after mixing I simply checked the fuel temp and the dial. Took quiet a while to do but now I know the dial is pretty accurate.

 

. . . Is it possible a critical temp was exceeded and a mishap ensued? . . .

 

Well it would be good to know what happened otto. It just googled and I never knew this, but KNO3 actually melts at 334C (633F). So perhaps that's what happened - perhaps he/she uses a gas stove or burner and a tall pot, and it overheated. We just don't know.

 

In actual fact, I reckon that anyone on this forum who posts regarding a potentially dangerous or hazardous incident, should be 'compelled' to explain as best they can the events that lead up to it. For their own safety and that of others. Failure to comply would the result in being banned! te he. I am half serious though.

[Arthur]

Yeah true Arthur, but how would the mix be at 250C? Sugar melts at around 186C - ...

 

Sugar will melt, pot nitrate will melt, the temperature of a pile of solid will be very variable according to localised heating and effectiveness of stirring. I would never be surprised if the inside of the mixing pot reached 250c

[dave321]

always thought the process of melting the two solids together

was bit dodgy to say the least

 

the heating and avoidance of hotspots is just too tricky to control properly

..........not worth doing in my opinion

[stix]

 

. . . I would never be surprised if the inside of the mixing pot reached 250c . . .

 

Well Arthur, I "would" be surprised, but it's not impossible.

 

I did a series of tests and people can take this which way they like. I did the tests using various fuel mixes. I used an IR thermometer and my nose as the measuring device.

 

The first test involved simple melting of KNO3/Sucrose (standard 65/35 mix) in 2 different electric skillets, No matter how much I could turn up the temperature (approx. 220C on full) it did not ignite.

 

I then decided to up it by recklessly melting in a frypan over a gas stove!!. The max temperature that was reached was 310C. A stage of liquidity was reached (KNO3 melting?) and finally a dry foul stinking mess. Nevertheless there was no ignition.

 

I challenge anyone to do these tests, If I'm incorrect then I'll happily learn something.

 

always thought the process of melting the two solids together

was bit dodgy to say the least

 

the heating and avoidance of hotspots is just too tricky to control properly

..........not worth doing in my opinion

 

Lets look at it in this light. If you follow a simple set of procedures, then making r-candy is 'relatively' safe and no need for hysterics.

 

In my opinion the OP simply fucked up and didn't understand the basics.

Edited June 30, 2016 by stix

[dagabu]

Stix,

 

That sure is interesting, I have been able to light off the remains inside my pan easily, once smoking, it flames up right away. I did make a change some years back and now use an electric skillet with refined Safflower oil and put another pan in that (double boiler?) to give me even heat across the surface. Safflower has a smoke temp of over 500°F!

 

Impossible to fire off R-candy using an electric double boiler?

[stix]

Stix,

 

That sure is interesting, I have been able to light off the remains inside my pan easily, once smoking, it flames up right away. I did make a change some years back and now use an electric skillet with refined Safflower oil and put another pan in that (double boiler?) to give me even heat across the surface. Safflower has a smoke temp of over 500°F!

 

Impossible to fire off R-candy using an electric double boiler?

 

Yeah it's weird, I was surprised - it's the first time I've ever tested r-candy in that way. I did around eight tests. It doesn't seem right but that's what happened in my case.

 

This wasn't the best testing I've ever done, nothing was written down. There are also a couple of things that may be playing a part.

 

The test pieces were small for obvious reasons, around half a gram from previous cast strands. Perhaps with a few hundred grams of the stuff - the heat builds up? Some of the test pieces were from fuel strands that had carbon black - but not all of them - some included sorbitol, dextrose etc. - there were various types and I didn't test all types using the same method.

 

To be sure, the final test I did was a freshly mixed 5gram batch of standard powdered 65/35 KNSU. Put in the non-stick pan on the gas stove, mixed, it did all the usual melting, then caramelised, badly, I turned the gas up as much as possible, it turned black and smoked for about 5-10 minutes until the smoke had gone - no ignition? The highest reading was 310C.

 

Yeah, I like the 'double boiler' method and bought an oil filled pan. Took a bit of getting used to though.

Edited July 1, 2016 by stix

[dagabu]

I finally bolted the two pans together (stainless steel pan on top welded a 3/8" bolt to the bottom and through the electric skillet to a nut underneath it. A simple smear of RTV (let completely cure) sealed it nicely. There is an inch gap at the corners (round SST pan in a rectangular skillet) to pour off the oil and refill it.

[MrB]

Dagabu, wont that just move the hotspot from the "ring" where the heating element is located, to where the welded nut is? The metal will transfer the heat more effectively then the oil.

I guess one way to test it is to see where the first bubbles show up, and where it boils earliest, if you try heating water on it.

B!

[dagabu]

Dagabu, wont that just move the hotspot from the "ring" where the heating element is located, to where the welded nut is? The metal will transfer the heat more effectively then the oil.

I guess one way to test it is to see where the first bubbles show up, and where it boils earliest, if you try heating water on it.

B!

 

Nope, the heat does not radiate up the bolt at all. The heating element is in a circle in the pan, most are. The bolt is in the center and can only heat up as much as the pan in that location can. The bolt is immersed in oil which draws off heat and the pan above is immersed as well drawing off any heat spikes. The bolt and nut are also completely isolated by RTV, they do not touch the metal pan on the bottom.

 

I also used my thermomelt marker to gauge any hot spots in this pan when I made it, it's a 204°C stick, and it did not turn at any point in the upper pan. That is well below the ignition point of R-candy.

[stix]

Dagabu, wont that just move the hotspot from the "ring" where the heating element is located, to where the welded nut is? The metal will transfer the heat more effectively then the oil.

I guess one way to test it is to see where the first bubbles show up, and where it boils earliest, if you try heating water on it.

B!

 

B! 'hot spots' didn't make a difference in my tests, and if you read what I did, it was taken to a limit far beyond possible occasional hot spots. Therefore in my view Dag's double boiler should be fine.

 

 

. . . That is well below the ignition point of R-candy. . .

 

What IS the ignition point of r-candy? I haven't seen it yet. I'm beginning to think that there may be some impurities in my KNO3?

Edited July 2, 2016 by stix

[dagabu]

About 800°F but there are a LOT of variables to that statement. It could go as low as 580°F according to tests done by Yawn.

Edited July 2, 2016 by dagabu

[stix]

About 800°F but there are a LOT of variables to that statement. It could go as low as 580°F according to tests done by Yawn.

 

I guess that would be Jimmy Yawn?

 

Well if those stats are correct, then the lowest ignition point of r-candy 580F is 305C which correlates with my own testing in that it did not ignite at that temperature. If I could have gone higher to 800F (426C) I would have. It was frustrating not to see ignition.

 

The question then has to be asked, why all the hoopla about the dangers of making r-candy?

 

For those that do, please check that your pan thermostat works. Be careful, don't leave it alone, if it starts to smell like burnt sugar then turn it off.

 

Perhaps a dislike or disregard for the legitimacy of r-candy by black powder rocket experts has lead to some mis-information???.

Edited July 2, 2016 by stix

[dagabu]

That is mostly because an electric skillet, right over the element can easily reach 800 degrees. I have temp sticks for preheating metals prior to welding up too 1000°F and with a dry pan, outside in the sun on a hot day, I got some color change right over the thinnest part of the element. 990°F?

[MrB]

 

Nope, the heat does not radiate up the bolt at all. The heating element is in a circle in the pan, most are. The bolt is in the center and can only heat up as much as the pan in that location can. The bolt is immersed in oil which draws off heat and the pan above is immersed as well drawing off any heat spikes. The bolt and nut are also completely isolated by RTV, they do not touch the metal pan on the bottom

.

 

Sounds very nice. Thanks for sharing.

 

 

B! 'hot spots' didn't make a difference in my tests, and if you read what I did, it was taken to a limit far beyond possible occasional hot spots. Therefore in my view Dag's double boiler should be fine.

 

 

Truth be told i see "other" uses for this. The whole concept, of creating a even heatsource, cheaply, is neat.

B!