Pique the Geek 20090703. Irregular Post: Fireworks Safety

(noon – promoted by Nightprowlkitty)

Since tomorrow is Independence Day and many folks will be displaying fireworks, I thought that this would be appropriate.  Amateur use of fireworks sends many people to the Emergency Department every year, and if I can reduce the number of calls there my work is well done.

Many of you do not realize that I am a Certified Ammunition Handler, bestowed by the United States Army.  I received that certification whilst I was directing the research and development of defensive and less than lethal pyrotechnic devices several years ago.  I also understand the chemistry and physics of explosives.

There are two main classes of explosives, low explosives and high explosives.  Most fireworks are in the former category, but there are exceptions.

Loosely, a low explosive is a material, usually a mixture, that burns really fast, but below the speed of sound.  A high explosive is a material, often a pure substance, but sometimes a mixture, that burns so fast as to have the flame front to be supersonic.  The former kind of burning as called a deflagration, whilst the latter is a detonation.  Deflagrations are useful for things like propelling bullets or other missiles, bursting a firework shell, or other fairly low energy applications.  Detonations are use, for the most part, for demolition work and military bombs.

Consumer fireworks fall into only a couple of classes.  With the exception of “snakes” (the tablets that you light and they produce a lot of ash) and smoke “bombs” (little spheres, usually, that you light and they just make pretty colored smoke), they are either sparklers, firecrackers, bottle rockets, sky rockets, and mortar rounds.  There is one other, the “ground flowers” that are essentially rockets without a stick.

Snakes are pretty safe.  They burn slowly, give off quite a little smoke, and just make a stain on the concrete where they are placed.  I have never seen or heard of an injury from them, but if one were to happen to put them in such a place that it could roll off and strike you, it is possible to get a burn, but they are pretty safe.  The only caveat is that, many decades ago, they had mercury in the formulation, so if you find some in Granddad’s attic, you probably should not breath the fumes.  The modern ones are formulated without mercury.

The smoke “bombs” are pretty safe, but I would not recommend that anyone breath the smoke.  Most of them are based on sulfur as a fuel, and the sulfur dioxide is very irritating.  The dyes the produce the colors are not good to breathe, either, but with good ventilation they are fine.  This is an appropriate time to say that no firework should EVER be used inside.  I have never heard of one of them exploding, but the casings are hot for some time, so do not pick them up until they cool.

Sparklers are much more dangerous than commonly accepted.  The old kind are steel wired dipped in a pyrotechnic mixture that has aluminum and iron powder, combined with an oxidizer (usually potassium chlorate) and a binder (often gum arabic or polyvinyl alcohol).  These burn extremely hot, over 1500 degrees F.  Lighting just one at a time is not such of a problem, but if several are alit at once, disaster can result.

CAUTION:  Science Content.  One of the rules of pyrotechnics is that a “gassy” mixture (one that gives off gases like sparklers do) is confined, it burns faster.  A single sparkler is not confined.  But if you put three or four together in a bundle and hold them in your hand whilst you light them, the interior of the bundle undergoes an extreme pressure increase once they take light.  This can cause a flame front to run down the center of the bundle in less than a second, scorching the hand holding them when it hits the bottom.  You can not let go fast enough to prevent the burn.  I know this from personal experience.  It happened to me before I had studied pyrotechnics, and only years later learnt the reason why.  NEVER light more than one sparkler at a time, ever.  Also, be careful of the hot wires for several minutes.

The modern ones are paper cylinders filled with a sparkler mix, but those will do the same thing if bundled.  One at a time, please!

Firecrackers are likely the most commonly used firework, and, if used with some sense, are relatively safe.  The Consumer Product Safety Commission has established standards for maximum loading of them for years now, and it is unlikely that serious injury would happen to you even if you were unfortunate enough to have one go off in your hand.  However, I do not recommend that practice.  Fireworks are made in bulk, and very cheaply, so it is quite possible to get one or more with more bursting charge than allowed.  In addition, the mix in them is the second most treacherous one (chasers and whistles have the first) commonly encountered.

Firecrackers are generally pieces of kraft paper wrapped around a flash powder mix, then a fuse inserted and the whole piece glued.  They are almost without exception made my hand, usually in China.  Quality control to produces tens of millions of these devices is pretty lax to sell them at the price that they command.  The mix is exceptionally dangerous.  It is roughly some atomized aluminum, an oxidizer, usually potassium nitrate or chlorate, and a little sodium bicarbonate to keep it from deteriorating.  One firecracker is fine, but making the mix for a batch is a horrifying experience.

The “M-80” is a the military version of it (they have not been manufactured for decades in a military setting, when they were used in a series on long fuse as a machine gun sound simulator).  Without giving away the recipe, because I never want my series to be a “cookbook”, here is how they were made, and firecrackers are done pretty much the same way except that small amounts of the finished mix are brought into the rolling area for firecrackers.  One real M-80 would fill over a hundred firecrackers.

The ingredients (atomized aluminum, an oxidizer, and and a sensitizer) are measured out into each M-80 shell separately, a paper cylinder into which a plug had be fit into the back end of it. After that, a plug is glued into the front end, and then the whole bunch of them put into a drum of sawdust and taken to a remote shaker. The doors are closed, the barricades put up, and the drum of several hundred M-80s are shaken for half an hour or so to blend the mix. After shut down of the shaker, half an hour is allowed to make sure that no static charge is left. Then workers wearing antistatic gear and military gas masks go in, pour out the devices, and then pierce the front plug with a sharp pick, then insert and glue in a fuse.

That is pretty much the protocol.  The reason is that the flash powder, unlike most other low explosives, can become “high order”, or can detonate only because of the weight of it in a bucket.  Keeping it separated into individual components obviates that.  The other reason is that this mix is exquisitely sensitive to minor static discharges, so the necessity for anti static gear.  I wore antistatic shoes every day when I worked with pyrotechnics.

Rockets are almost always lifted by black powder.  Interestingly, this material was developed in China over one thousand years ago and still has no peer for some uses.  True, “smokeless” powder (a mixture of glycerol trinitrate (nitroglycerin) and cellulose trinitrate (guncotton) is the preferred propellant for modern firearm cartridges because it leaves little corrosive residue in the action and barrel of the firearm, and little smoke of the battlefield.  But smokeless powder has one serious shortcoming:  it is inherently unstable.  To formulate a smokeless powder stable enough to have a decent shelf life requires the addition of up to several per cent of stabilizers, and they are used up over the years to neutralize the acidic decomposition products of smokeless powder.  For those of you with WWII vintage ammunition, I would suggest that you ask the hazardous materials folks to come and take it.  Same thing with Korean War vintage, and Viet Nam vintage is not far behind.  But black powder, if kept dry, keeps, unchanged, essentially forever.  There are samples from the Revolutionary War that are just the same today as when it was first made.

Black powder is very static sensitive, as most low explosives are.  It packs quite a punch, and was the lifting charge of choice in the defensive smoke grenade that I designed for the Army.  Just potassium nitrate, charcoal, and sulfur, it will keep forever.  The large amount of sulfur serves as an antioxidant for centuries.

Anyway, all rockets use black powder, in some form, as the lifting charge.  The large ones use quite a lot, usually mixed with some wax to slow down the burn rate.  You do not want the rocket to blow up at launch, but rather later.  The smell of fireworks is almost completely associated with the smell of burning black powder.

Bottle rockets are essentially a big firecracker on a small rocket.  The black powder charge lifts the little rocket, and as the engine burns out, it connects with a firecracker, thus making the “report”.

Larger “skyrockets” work on the same idea, except the payload can be different, such as stars (quiet but colorful bits of light, separated by another black powder charge), bees (loud bits of light, usually with color, also separated by a black powder charge), or other special effects, almost always separated by a black powder charge).

Mortars are not much different from rockets, except that their black powder charge is contained in a stiff tube, and the blast from that propels the shell from concussion rather than from aerodynamics.  The colorful fills are ofter larger, since the propellant does not have to fly with the payload, so the payload can be larger.

Well, I intended to talk about safety.  Here are the rules:

1  NEVER let a small child light fireworks

2  NEVER trust a fuse.  Fireworks are assembled very cheaply, and so are the fuses.  The fuse on one might take six seconds to ignite the display, and the next one might take less than a second.

3  NEVER imbibe on psychoactive substances and display fireworks.  Things can happen very, very fast and even with good wits things can turn out very, very wrong.

4  NEVER allow a small child to “help” you ignite a fuse.  If things go wrong, you will have your hands full saving yourself, let alone a kid.

5  NEVER hold a firecracker in your hand and light the fuse.

7  ALWAYS know where your rockets are going.  My house has been hit three times already this season.  Fortunately, no fire here yet.

8  LEARN when to quit.  It the wind comes up, or if your fireworks are not doing what you expect, quit to use them another day.

9  ALWAYS keep fireworks under a shelter, and take them out one at a time.  One unfortunate shot can make the whole pile go up in an extremely dangerous manner.

10  NEVER do as Mrs. Translator and I used to do, with the friends and kids, and have a bottle rocket battle, using hollow pipes as aiming devices, with one person aiming and another loading and lighting.  No one in our parties were ever hurt, but it is not a good idea in any regard.

11  Sparklers are much more hazardous than we are led to believe.

Any recollections about your fireworks experiences would be welcome, and to all, a very Happy Independence Day!

Warmest regards,

Doc

Crossposted at Dailykos.com