Educate me on BP and static(I know, dead horse)

[Pulp]

I know that normal static discharges will not ignite commercially made BP. I have heard that this is due to the graphite coating over the kernals of powder. True or False

I have also heard the graphite coating is to help reduce clumping and increase flowability, not to reduce chances of a static discharge ignition. True or False

I would assume that the more finely ground the BP is, the more susceptable to static discharge ignition it would be. Sorta like flour dust can go BOOM big time. Would my assumption be True or False.

I make my own BP from time to time, (in very small batches) and I do not have the facilities to put graphite coating on it. It does not flow through a measure worth a flip, so there is some evidence the reason for graphite is to improve flowability. I haven't tested it for static discharge ignition.

The reason for the question is; there is an ongoing fight on another forum about static electricity in a fireworks plant. Operators going into certain rooms must touch a copper grounding pole as they enter the building. I know fireworks often contain superfinely ground BP. Anyway, one poster says not touching the pole could cause a static discharge ignition, the other poster says it flat out cannot happen.

In my poor little old mind, I can visualize BP dust floating in the air and being ignited by a static spark. Of course my poor little old mind could be hallucinating.

The one thing I know for sure: if I went into a fireworks plant and was told to touch a copper pole before entering a certain room, you can bet your bottom dollar I will touch the pole.

 

[mykeal]

All by itself, black powder will not ignite from exposure to static electricity, whether it's coated with graphite or not. The graphite does reduce clumping and makes it flow better, and there is some benefit to reducing resistance and thus reducing the effects of static electricity (more about that later).

Here's the physics: black powder is ignited by heat - heat it up to the ignition point (about 750 degrees F) and it will go off. Static electricity by itself contains no heat; it's pure electrical energy and light. However, passing electricity along the surface of or through a solid body can cause heat buildup, as all materials have some degree of resistance to passing electricity. It's that resistance that causes the heat. The tungsten element on an incandescent light bulb is a good example of what happens when electricity flows through a highly resistive material.

The materials in black powder are all good conductors of electricity; that is, they contain low or very low levels of resistance. When exposed to a static electricity discharge they will pass the electrical energy through rather than resist it's flow, and thus there is very little heat buildup. A graphite coating helps this process since graphite is a very good conductor; the electricity is passed along before it even reaches the materials underneath.

The problem with black powder and electricity comes when there are contaminants in the material that are highly resistive. A tiny metal shaving will heat up very, very quickly and thus can be the source of ignition if present in the powder when exposed to electricity.

As regards fine dust particles of black powder, they are no different than dust from sugar, grain, coal and other common materials that have been known to ignite; they can support an explosion. Again, a source of heat is necessary to start the reaction (regardless of the material), and static electricity passing through a resistive element meets that criteria.

 

[Skinny 1950]

A static spark has a temperature of >10,000 degrees Kelvin, it ionizes the air and forms plasma which has a very low resistance. You may have seen plasma cutters at work hacking through steel like it is butter.
Static electricity such as the charge you get from walking on synthetic carpet or getting out of a car with plastic seat covers can have a voltage well in excess of 25,000 volts which at normal humidity will form a spark about an inch long.
High voltages tend to travel at the surface of objects in its path and always takes the path of least resistance, in the case of a discharge the ionized air has a far lower resistance than gun powder grains and so the grains will not be hit.
The reason for adding graphite to gunpowder is that gunpowder is made up of potassium nitrate (poor conductor) charcoal (somewhat conductive) and sulfur (poor conductor) so when mixed it is a pretty poor conductor of electricity.
The graphite makes the powder a better conductor and so if you have a lot of it it will not tend to build up a static charge on it's own (this charge can be positive or negative with respect to neutral ) and this makes the gunpowder safer than non graphite powder.
If the gunpowder is charged and you carry an opposite charge when you touch it or come close enough for a discharge the plasma will hit the powder and it will go off.
If the powder is coated with graphite the plasma will bypass the powder and go straight to the object on which it is resting.
That is my theory and I am sticking to it.

 

[Jim Watson]

I don't worry about static and BP. If I were milling my own, I would worry some about static and any sort of airborne dust. I would worry more about the mill crushing the wrong crystals.

The only explosives plant I ever visited furnished conductive shoes and had grounding plates at the doors.

 

[mykeal]

There is a discussion in the Black Powder Essentials sticky thread worth reading:
http://www.thehighroad.org/showthread.php?t=414231