SENSITIVITY OF BLACK POWDER TO STATIC DISCHARGE By Wayne McLerran
It’s been many years since I designed and published an article on a semi-automatic black powder (BP) loading system consisting of an electronic powder dispenser, digital scale, fiber optics cable, a tall stand and a drop tube. By pressing a single button the dispenser trickled out a precise charge of BP down the drop tube into the case setting on the digital scale platen. The dispenser stopped when the scale registered the programmed powder weight to within +/- 0.1 grains. Knowing this, a fellow shooter recently asked if I was concerned about using the setup with black powder since the dispenser is constructed out of plastic and has a plastic reservoir which potentially could build up a static charge. Prior to building the loading system and due to a similar concern, I researched the subject extensively, experimented with subjecting BP to high voltage static discharges, and was convinced that any static charge created by the dispenser would not be sufficient to ignite BP. 20 years later I continue to use the same setup without any problems. But the subject continues to come up in many of the online BPCR forums and is therefore worthy of additional discussion.
My experiments with attempting to ignite BP consisted of the following. Using Goex 2Fg and 3Fg I first pounded it to dust with a hammer with no reaction. Several piles of the dust were then subjected to high voltage discharges of approximately 100,000 volts with a hand tester used to test static discharge damage thresholds in integrated circuits. The discharge caused some of the small granules to move but none of the samples ignited. Around the same time a fellow by the name of Barry Bush published two excellent and lengthy articles on BP safety in the 1999 spring and summer editions of The Black Powder Cartridge News.
Mr. Bush is obviously a very knowledgeable guy and did a good amount of experimenting to determine the sensitivity of BP to heat, pressure and static discharge ignition. He found BP much more sensitive to heat than smokeless. He also found that BP is not very sensitive to shock, and is much less sensitive to high voltage sparks than smokeless powder. Barry passed sparks of up to 20,000 volts directly through BP with absolutely no ignition. Goex Fg, 2Fg, and 4FA (unglazed powder) BP was used. The 4FA powder was used to see if the lack of graphite would allow the powder to ignite. He said that it is conceivable that a 100,000-volt spark from a fingertip could ignite BP, but the chances are very remote, which I proved to myself by my experiments detailed above.
In summary Barry said, “Many common perception of black powder come from those who lack practical experience, and they often reflect confusion with other explosive materials. Modern smokeless powder has an excellent safety record, but in some respects smokeless can be more dangerous than black: it is more likely to give extreme pressures from an overload, more susceptible to decomposition, and under some conditions, more sensitive to electrical discharges.” In closing he further stated, “Black powder has managed to outlive most of its detractors, and hopefully will continue to do so. Meanwhile, shooters can ill afford to repeat folklore, speculation and hearsay which may come back to haunt them.” The last sentence refers to past and possible future government regulation on BP due to incorrect and misleading information.
To further reinforce the above comments that BP is not sensitive to static discharge, go to the following links at the Connecticut Muzzleloaders website: http: //www.ctmuzzleloaders.com/ctml_experiments/sparks/sparks.html and http://www. ctmuzzleloaders.com/ctml_experiments/electric_ignition/eignition.html. The spark experiment is similar to the ones both Barry Bush and I ran. The key to understanding the differences in the two ctmuzleloaders.com experiments is the high voltage sparks in the first experiment and those in Barry Bush’s and my experiments do not contain sufficient energy (power) to heat the BP particles to the ignition point. Electrical power (measured in watts) is the combination of voltage and current. Static discharges generated from friction on plastic containers or sliding ones foot on carpet and touching another object are typically at very high voltages but the current levels are very low. The second ctmuzleloaders.com experiment was based on using a capacitor, an electrical energy storage device to ignite the powder. Although the voltage level was significantly lower the capacitor provided a much higher current source when discharged through the powder, which was sufficient to heat the powder to the ignition point.
Another question that comes up now and then is based on concerns about static buildup on plastic containers used for shipping and storing BP, especially when pouring the powder out of the container. What many BP shooters do not realize is the containers are made of antistatic plastic. Although antistatic plastic can be made in several colors, clear, red, etc., the plastic containers BP is shipped in are typically black and contain small amounts of carbon to make the plastic slightly conductive to electricity (antistatic). So pouring BP out of the containers cannot build up a static charge.
The development of antistatic plastic was the result of the semiconductor industries need to reduce the cost of shipping integrated circuits (ICs) in the 1980’s, which were commonly shipped in "conductive" aluminum tubes at the time. Some ICs are sensitive to even low levels of static discharge. Most of my career was spent in the semiconductor industry and I remember reading at the time that materials with a surface resistance of as much as several hundred thousand ohms per square inch would drain away any static charge. Using a standard VOM (volt ohm meter) or multi-meter, one can actually determine if the plastic used in BP shipping bottles is antistatic.
While writing this article I grabbed a black plastic bottle of Swiss 1.5Fg and my handy Harbor Freight multi-meter, the one they give away if you purchase anything at the store. With the meter set on ohms and the sharp-tip probes inserted into the plastic about an inch apart, the resistance was around 300,000 ohms, sufficient to eliminate a static charge buildup. Just to double check, I also used an expensive multi-meter with the same results. By the way, typical non-treated plastic is an excellent insulator (has extremely high to infinite resistance) and therefore will not drain off a static charge unless ambient humidity levels are high; it’s wet or sprayed with a conductive material, which brings me to some solutions if you are still concerned about static charges building up and igniting BP.
Plastic powder-dispenser reservoirs can be lined with aluminum foil, sprayed with Static Guard or other brands of antistatic sprays to lower the surface resistance and drain off static charges. Spraying with a water-diluted detergent solution and allowing the surface to dry will temporarily eliminate static buildup as will wiping with a fabric softener sheet used when drying clothes. Or go to the following link (http://www.instructables.com/id/Creating-Anti-Static-Spray/) to easily make a solution from three common household ingredients.
I'm certainly not suggesting one can be careless when using BP, but the experiments discussed here and the additional information presented should cause you to reconsider the warnings and unsubstantiated myths we in the shooting community have been passing around about BP safety.