17 replies to this topic

[pyrotechnist]

Ok I know flash is sensitive etc but if it is as sensitive as people make out when anyone mentions about mixing it or handling it etc then why do salutes never seem to go off when it is being fired out of a motor. The amount of force and the impact of that from the black powder under the device to propell it out of the tube should surely cause it to violently move inside. The same also goes for any sort of cake etc where flash is used. They way a lot of these cakes are handling it surprises me that they don't go off but they do not. I am sure these are two very valid questions so if anyone cares to explain please do.

[StephF]

Ok I know flash is sensitive etc but if it is as sensitive as people make out when anyone mentions about mixing it or handling it etc then why do salutes never seem to go off when it is being fired out of a motor. The amount of force and the impact of that from the black powder under the device to propell it out of the tube should surely cause it to violently move inside. The same also goes for any sort of cake etc where flash is used. They way a lot of these cakes are handling it surprises me that they don't go off but they do not. I am sure these are two very valid questions so if anyone cares to explain please do.

If I could add my unqualified two penn'orth.

My guess would be because it is unpredictable, you could do the same things to it ten times out of eleven and nothing happens then the next time kabloowey !

[seymour]

Ok I know flash is sensitive etc but if it is as sensitive as people make out when anyone mentions about mixing it or handling it etc then why do salutes never seem to go off when it is being fired out of a motor. The amount of force and the impact of that from the black powder under the device to propell it out of the tube should surely cause it to violently move inside. The same also goes for any sort of cake etc where flash is used. They way a lot of these cakes are handling it surprises me that they don't go off but they do not. I am sure these are two very valid questions so if anyone cares to explain please do.

People do legitimately warn others about the dangers of flash powder. Other people excessively do this and exaggerate the sensitivity.

In reality, flash is sensitive enough to be used without accident if used correctly. While the lifting of a shell may seem to be very violent, the shock is reduced by a fairly slow acceleration (compared to the almost instant negative acceleration that you might get if that shell suddenly hit a stone wall). Even with an abrasive material such as Titanium, this is unlikely, as shown by practice to go off. However, even if it were to go off, it would be far away from people.

It is very important to remember that the sensitivity is not the only issue when considering the danger of a composition. While the sensitivity of many flash powders is less than some stars, the consequence of an ignition is not burns, but potentially limbs missing, or a red mist and meaty rain.

Going back to the physics of a shell (or in this case salute) being lifted,ignition is much more likely in some situations - such as the use of scissors- which could easily be done if not aware of the risks. Scissors, two blades of metal scraping together, or a shoe with all the weight of a large ape on a piece of gravel, could easily put more energy on a very small local area than a shell experiences during lift. And in these situations, you are standing right there.

Note that I am talking about the safer flash powders. There are some formulas that I'm sure would go off from a shell being lifted.

Edited by seymour, 02 July 2009 - 09:53 AM.

[pyrotechnist]

Ok thank you both for the replies I guess that makes sense though I guess in the long run it all balls down to good luck . I hate flash powder but that just stumped me a little.

[Green_as_my_powder]

I am more ignorant than most, but I try to make up for my ignorance (gradually, of course) by doing tests. I too was concerned about the sensitivitiy of flash since I have almost no experience. From reading, it seemed that whistle mix was the most sensitive of the flash powders I use (more sensitive than general purpose H3 or other aluminum based) so I did a series of tests trying to get it to ignite. I posted the details of these tests awhile back. The final test was hitting a small paper canister full of whistle mix with a high speed bullet (several times). The bullet was copper jacketed, and the canister was mounted on wook--no spark. None of the tests resulted in ignition. For my own sake, I think the danger is mostly from spark and less so from mechanical impact. Certainly not conclusive, but I'm more comfortable working with flash after doing these tests.

[Green_as_my_powder]

I am more ignorant than most, but I try to make up for my ignorance (gradually, of course) by doing tests. I too was concerned about the sensitivitiy of flash since I have almost no experience. From reading, it seemed that whistle mix was the most sensitive of the flash powders I use (more sensitive than general purpose H3 or other aluminum based) so I did a series of tests trying to get it to ignite. I posted the details of these tests awhile back. The final test was hitting a small paper canister full of whistle mix with a high speed bullet (several times). The bullet was copper jacketed, and the canister was mounted on wook--no spark. None of the tests resulted in ignition. For my own sake, I think the danger is mostly from spark and less so from mechanical impact. Certainly not conclusive, but I'm more comfortable working with flash after doing these tests.

Sorry...dumb fingers. The canister was mounted on wood.

[dr thrust]

from my readings static build up, either by storage in a plastic container/using a plastic spoon, and or the static you yourself can create by movement poses the greatest risk whilst handling flash, fit an earth plate and if storing flash, use wooden container etc.
As for whistle all i know about that is from my experience of whistle rocket motors containing titanium metal powder this increases the risk of ignition and should be kept to less than 7% of the comp to stop it going off in your face on the press!.
ho heres a nice video on static just incase you think im talkin bo##ocks whoose!

[seymour]

From reading, it seemed that whistle mix was the most sensitive of the flash powders I use (more sensitive than general purpose H3

Neither whistle nor H3 are flash powders.

[50AE]

Also, while working with static sensitive compositions like flash, you must make sure that the local humidity is +50%. High levels of it lower drastically the chance of a big static charge accumulation. As the others above me said, you shouldn't use plastics. Use a cardboard or wooden case to put your flash powder in. Also wearing synthetic clothes can be very hazardous, wear cotton.
Static poses the most big dangers to volatile fuel/air mixtures. As you can see from the video that chris m posted, gasoline fumes mixed with air ignite with ease. There was similair accident reported in APC. A guy was using acetone for binding stars if I remember correctly, when spontaneously the fumes self ignited, firing all his compositions and chemicals.

Edited by 50AE, 04 July 2009 - 02:26 PM.

[pyrotrev]

Also, while working with static sensitive compositions like flash, you must make sure that the local humidity is +50%.

This could be a little difficult to arrange to order in some places unless you happen to be God or are very good at rain dances! Thankfully it's rarely less than 80% round here, and I use static safe equipment for all sensitive comps.

[Mumbles]

It's not really an arranging thing, as much as it is working when the conditions are correct. If there is low humidity, don't make flash, period. If you have a dedicated pyrotechnic building, a humidifier can probably be used. A noted manufacturer recomends making flash first thing in the morning so it is still cool, and has a higher relative humidity. You're also fresh and concentrated, and less likely to make a mistake.

I am also a fan of lots of static guard spray.

[50AE]

I was talking about a dedicated pyro building. You can't really control the humidity outside.
By the way, do you know if this static protection spray can be home made ? I heard it was water + something sticky.

[pyrotechnist]

Hm interesting but wouldn't the fabric softener contain some sort of sodium compound making it useless for coloured stars? On the flash side again I have read on this forum that supposedly the army mix flash in the containers within a rock tumbler. If this is the case then surely static could potentially build up and cause one or more of the containers to explode but it doesn't seem like it does.

[Mortartube]

I have heard that the rock tumblers used for flash by the military have anti static precautions. Probably something like a copper brush rubbing on the container and linked to an earthing rod.