Mysterious Shock Received When Operating Fire Extinguisher...

Sounds to me like you had a static charge build up from the flow of the fire fighting chemical in the discharge hose of the fire extinguisher.

Not positive that your answer lies in here, it may. Interestesting read though and a lot of it I think would pertain to your facility. V belts are mentioned as being builders of static charge.

http://docs.google.com/viewer?a=v&q=cache:7mc-LXP9KO4J:www.osh.dol.govt.nz/order/catalogue/archive/staticelectricity.pdf+static+discharge+through+non+conductive+powder&hl=en&gl=us&pid=bl&srcid=ADGEESjMW_GFfvQNErwb2D1evJT0hfsbq7MOuTyMTxGL1iDD9y-WctZUi_ZInbPHNAjGCL5z74heKnrjH4NVOst-ljklGoB1KbPBg6w1v-vz438Tk5my8eSd3T_dkavrqSJalE_dmOFR&sig=AHIEtbTgV4F73vW6OF1_TGyS-g_hHWyfZQ

My theory, for what it's worth, is that a static charge traveled through the extinguisher powder to your worker, finding ground through him.

Non conductive materials can carry a serious static charge........I'm thinking about silo explosions from excessive static charge build up in the dust.

Off the top-o-my-head, it sounds like electrostatic discharge cause by the non-conductive powder building up a charge as it left the extinguisher, due to extreme low temperatures and humidity.

If everything was dry the charge would have built up until it had enough energy to discharge through his well insulated boots and floor.

Any thoughts?

I was kind of thinking the powder was involved, (had to be), but the static charge traveled back from the equipment to the worker through the powder.

Maybe the friction from the v belt, combined with the super dry air created a static charge on some part of the equipment that was not grounded. This could probably just be a plastic shroud.........or almost anything else.

You said "ABC dry chemical, handheld fire extinguisher."

For use on electric fire the extinguisher must have an "E". Letters A,B,C,E etc. designate catagories

Please take care in future.

Hi mountk2,

Are you thinking that ac current traveled back through the powder?

That seems like it would be odd.

Can abc dry chemical conduct regular electrical current?

I was on the fire team in the Navy, (US) and we only had three classes of fires, A-alpha, B-bravo and C-charlie.

Reading this, I think the fire extinguisher itself, as well as the dry powder used would be fine for all three, hence the ABC.

http://en.wikipedia.org/wiki/Fire_classes

Hey,

E is appropriate in some countries.

I'm stuffed!

True, but ABC dry powder is also appropriate for class E fires.

I'm stuffed too! I must be getting old, it sure didn't seem to take much to get me there. Had a hard time finishing one plate.

Sawmill......did that fire extinguisher have a plastic horn on the discharge end?

I'm thinking powder interacting with the horn. Some of these plastics will build/ carry a hell of a static charge. I've got a robe that is 100% polyester, if I shake it around in the dark, especially in the dry air of winter, it'll produce a light show of static sparks.

Of course, you are right.

Just took a head count here. The cook and two of the boys are out cold. The 4 year old and 86 YO Granny are still awake, for now. I'm keepin' my fingers crossed that they will conk out too.

Cheers.

The four year old will probably wake up about the time you're ready for bed.

The more I think about it, the more I'm liking the idea that the static charge built up at the discharge end of the extinguisher, caused by the friction of the powder being released. The operator made a handy path to ground.

Seems plausible. The tingle caused by slight static charge, but not enough to jump through his boots to ground. The big whammy after the charge had grown significant.

What do you think?

If the static charge came from buildup in the piece of equipment, the shock would have been instant and happened on the first burst of powder.....no tingle.

I can't conceive of any way that a stream of dry powder could conduct electricity. If it did, I'd think there would have been some sparks jumping up the stream. And as the OP said, this electrical fire was more or less common. It must have had something to do with the conditions in that room, at that time.

I can conceive of a dry, non-conductive powder creating a big charge as it exits the extinguisher, and building up until it finally discharges through the man holding it.

I wonder what the extinguisher maker will have to say.

From wikipedia.

The flowing movement of finely powdered substances or low conductivity fluids in pipes or through mechanical agitation can build up static electricity.^[10

Yes, and lest anyone forget, the flow of no-polar fluids (such as gasoline, benzene, toluene, etc.) through a non-conductive hose will build up an extremely large static potential.

Polar solvents such as water, ethanol, methanol, iso-propyl alcohol are much more conductive and do not create substantial static charges.

The same is true of powders. Table salt with its ionic bond is much more conductive than the powders similar to Sodium bicarbonate that are used in ABC fire extinguishers. For example plastics flowing through a plastic tube will discharge within the tube as it flows, thus plastics are only transferred through metal pipes inorder to reduce the possibility of static generation.

Very good post!

Old Salt

There's this also......

http://ezinearticles.com/?A-Fact-Guide-to-Dry-Powder-Fire-Extinguishers&id=4116459

Designation of C is for electrical fires. There is not E designation.

A is for wood, paper, ordinary combustibles

B is for hydrocarbons such as oil, gasoline, grease, etc.

C is for electrical

D is for flammable metals such as magnesium

Old Salt (also local fire chief)

In firefighting, fires are identified according to one or more fire classes. Each class designates the fuel involved in

We don't know where mountk2 lives. There is an E class.

Thank you for clearing the confusion w.r.t. C & E classification mode. You made my life easier so GA classification to you.

You're welcome. I'm still coming to grips with the fact that this isn't just a North American forum. And, I've been here for awhile.

Damn you!

In the old days, when I was still working as a chef, we always had a bucket of old salt standing around. We served oysters on salt and when returned to the kitchen it landed in that bucket. Waste not want not.

Smaller oil fires (they happened all the time) were out in no time at all and the salt could be removed once done. Stopping a kitchen in full flight was not an option besides any fire extinguisher would have spoiled the broth.

Any complaints from the fire chief?

The use of a CO₂ extinguisher will not effect the food and leaves it fit to eat, only a little colder. I have put out several Thanksgiving turkey fires and Christmas goose fires with the CO₂ and the people invited us to stay and sample the food. Never did because dinner was waiting at home but could have.

Only those who used a dry chem extinguisher couldn't eat the vittles.

Keep some baking soda in your refrig with the top open. It helps reduce odors and is a great fire extinguisher. For pan fires, simple put the cover on it or keep a pizza pan close by in the cabinet for the same use.

Put out two fried turkey fires today. One we put out with CO₂ extinguisher and the homeowners continued to eat the bird later. Other the homeowner used a small dry chem on it and couldn't put it all out. They went to the drive-in line at McDonalds.

Old Salt

We should probably mention another of the main things to remember when experiencing a fire of any kind.............Don't panic and freak out, just calmly do what you need to do, whether it's putting out the fire or leaving the area.

EXCELLENT WORDS!

That is probably the most important factor in any fire situation. Well said.

Old Salt

Although it is off the main topic, you might find this article of interest since you have experience in the culinary arts.

"Thanksgiving Day fires in Residential Buildings"

http://www.usfa.dhs.gov/downloads/pdf/statistics/v11i5.pdf

It was just released by FEMA the the US Fire Administration. I found it interesting both from being a firefighter and also as a big fan of Thanksgiving foods.

Old Salt

Thank you. This is what I remember, but wasn't confident enough to say it.

While I am replying, I witnessed a demonstration at a firefighter's meeting of them spraying water from a fog nozzle directly on a high voltage grid. The voltage did NOT come back the fog stream because it is made up of discreet droplets, not a continuous stream of water. I would interpret the ABC powder stream as being similar. However, static voltages can be huge, and I'm not familiar with what they can do in the way of jumping across a bunch of tiny gaps.

As far as the powder stream building up a static charge in the extinguisher horn--I doubt it, because the discharges, even the "long" one, were fairly short, and I don't think they would build that much charge is such a short time.

Use of a fog stream on electrical items can be done but is very dangerous, risk analysis says don't do it because of possibility of a continuous stream forming from a bad nozzle. Also now many fire companies use what is called a combi nozzle. Pulling the bail handle back and it controls a smooth bore stream from the middle of the nozzle, twist the end of the nozzle and a fog stream starts from near the outer perimeter of the face of the nozzle. Twist the nozzle to vary the fog flow. Use the wrong stream and you could be a former firefighter.

The powders used in fire extinguisher are very poor conductors of electricity, if not they couldn't be used for class B electrical fires. This property makes them very prone to static electricty build up. The static build up begins at the cylinder and increases as it flows through the non conductive hose. When it gets to the non conductive horn or nozzle it is very charged which is even greater on a low humidity day such as an extremely cold day.

I have experienced static charges when I have used CO₂ extinguishers that didn't have conductive hoses. This is also a good way to tell which are old and need the hoses replaced with conductive hoses.

How is Louisville doing? I used to travel through there when visiting relatives in Minerva, Waynesburg and Canton. Not recently but some years ago.

Good Luck, Old Salt

I'm sorry,

You and Lehman57 have completely lost me.

What is a class B electrical fire? And, why is no one willing to admit that there really is a class E electrical fire?

I'm lost.

See the first line of #27--I agree with your designations.

Class B is not electrical, but flammable liquids. Class C is electrical. And, Yes, Class E is also electrical, but you have to be in Europe (or others) to do it.

Sorry, typographical error. Should be class C.

Keep the quick eyes going.

Old Salt

I figured as much.

Considering it is a very low humidity environment and you have a high velocity chemical discharge, I'd say it is a case of static build-up and discharge. These can be very painful and possibly dangerous.

Brings to mind the scene in "The Hunt for Red October" where a hovering helicopter is trying to transfer a passenger to surfaced submarine. In this case, the static charge build-up from the rotor motion can be lethal.

I agree with you. The line that really convinced me was:-

The weather was very cold, about -30C, and clear.

That means that humidity was way, way down.......eg. Static was the real problem. It still hurts though!!!

My take is that the extinguisher funnel/hose is plastic and may need to have some method of removing the charge (it could still cause an explosion in some hostile environments because somewhere there was a big spark at discharge time....), or be replaced with metal or similar....

An earth cable could be more dangerous with machines around and it stops being so portable.

Also the OP should contact the manufacturer for details about low humidity problems....maybe they have fixed the problems already.....certainly they need to be told.....

Hmmm. I call the sensation from AC shock 'tingle', but I call the sensation from static discharge "shock".

However, the situation involved an ABC dry chemical exinguisher. If the shock were due to the creation of an electrically conductive path through the spray stream from either the energized motor or V belt static, then both the first and second shocks would have been felt as soon as the extinguisher stream contacted either an electrically hot spot or charge build-up on the motor. I can't believe that the extinguisher's C rating isn't real, that the extinguishing material is actually conductive.

It appears from the description that the 2nd shock did not appear as quickly as the first shock.

>He gave the fire a short blast of dry chem from about 6 feet away and felt a tingle in his hands. He gave a second, longer blast of dry chem and was knocked over by the shock he received.

If the first shock was after a short spray, and the 2nd (more severe) shock was after a longer, extended spray, then the length of the spray would seem to be a key factor; the increased spray time building up a higher charge and causing a greater shock.

I think you're on the right track with static discharge, but static from the discharge of the extinguisher itself, not the V belts. I know static charge is so much more evident in the winter time with winter's lower relative humidity.

At the very cold ambient temperature there, did the worker have gloves on?

I wonder if ordinary worker's cotton/canvas or leather work gloves would have insulated him shock?

All,

Thanks for your comments and ideas. Some of our newest thoughts about the issue:

1. We aren't sure if the flow of powder through the nozzle would generate the voltages necessary to create a shock--if this was the case, then everyone would be getting static shocks when using fire extinguishers...

2. I have since found that V-belts are fully capable of building up static charges--significant enough to be of concern in industries where explosive atmospheres are present. New V-belts have a static-discharging surface but this lessens as the belt gets older. I'm trying to find out if our belts were old or new. Does anyone have an idea to calc how many volts might be needed to bridge a 6 foot gap? If that gap is filled with a nonconductive powder? Does static electricity, on a small scale, work like lightning--where something works to ionize the air between the two points before the main hit takes place?

3. Iris, I don't know if the worker had gloves on, but it is likely, at the temperatures they have to work at. Additionally, I don't know if the blower was running at the instant of the fire extinguisher discharge.

4. I am curious enough about this issue to purchase a hand-held piece of test gear called an "electrostatic field voltmeter". This should tell us for sure if there is any significant static buildups when discharging a fire extinguisher or around our V-belts.

Keep your comments coming!

Jon.

The lack of humidity caused the problems, not V belts......

The line:-

The weather was very cold, about -30C, and clear.

Tells it in one......I used to have to fix paper printers in winter with similar problems, inch long sparks from moving paper fast !!!The electronics had to be shielded from the effects.....the workers too!!!

The printers would run fine from spring through Autumn, but winter......was something else!!

GA for a GREAT answer!!!! Perfect!!!

Could you find out what the poor guy was wearing?

Polyester (synthetics) over wool maybe?

Did he run or move erratically for a longer distance to get to the fire?

Was he holding the (presumably metal extinguisher) in one hand and the insulated nozzle in the other?

It would warrant further investigation, like you said.

Hope all is well, Ky.

Interesting problem. I once worked at a plant that made polyfilms and these were wound in great rolls similar to paper mill rolls. If the film was not grounded, you would feel the static just walking in front of the windup machine. Operators would use a grounding wand 9attached to the machine) and pass it over the roll and then proceed to cut it while it was still moving (they used very sharp Richard knives) and start a new roll. The full roll would be removed. These rolls were grounded by using tinsel (like on a Christmas tree) draped over the roll and tied to the machine. They would last a few days and then were changed.

I have been zapped by big static charges that would knock you on your keester and had been momentarily (arguably) dazed . No one was ever seriously hurt by these discharges but you became more aware of them as you worked on these rolls. Most operators would go through a pair of steel toed boots because they would always be touching the machine to discharge the static to ground. Yes big static charges of many thousand volts can jump about 6 feet (rare) on these windups. I too suspect your belt and perhaps a tinsel wand could be used on it.

I can not see that it is the V-belt. I say this because your worker received a "tingle" the first time and then a shock the second. If the static charge had built up sufficiently and found a path to ground through him I believe that it would have discharged all at once.

Could your worker have been standing near that metal pipeline that you mentioned? Could that pipe have been hot and found a ground through the metal body of the extinguisher?

Failing that, I would be tempted to believe that it was the extinguisher itself (though I am curious if the initial "tingle" lasted a brief second or was an ongoing feeling while he was discharging the extinguisher… was it a sudden "shock" or was it a seconds long "tingle.")

I am guessing that the tingle was really the static raising the hairs on his arm as he neared the machine. When he was sufficiently close the big wham hit him. It may have passed through the extinguisher (not the discharge) as he pointed it by reaching towards the machine. Probably hurt his pride more than the operator. Scary the first time but you can become aware of the discharge and prepare to create a ground path (other than yourself) with a ground wand or some other device like the tinsel mentioned.

It is a problem with many winding mills. So the belt is my suspect. My expertise is by experience-observation as I am not an electrical man. I last worked on polyethylene extrusion back in the 1960s.

The shock was caused by static electricity at several points along the path.

The v belts could have generated a charge. The extreme cold certainly would have influenced this. The dry powder in the extinguisher with dry nitrogen is very prone to static electricity, discharge one at room temp and see how it sticks to smooth vertical surfaces (this is also why it gets all over everything you didn't want it on). The extreme low temp also exaggerates this property.

The hose of a dry chem extinguisher is not conductive like the hose of a CO₂ extinguisher in order to dissipate the static charge of the CO2 going through the no conductive hose. This is why the person felt the shock and combined with it his rubber boots were also effected by the extreme cold.

Take all these generators/conductors and there accumulative effect and you have one really big static charge. If it occurred at a warmer day and with some moisture in the air he wouldn't have noticed it because it would have dissipated before it got to him.

There have been many more accidents of this type with a worse outcome.

Cleaning the tanks of oil tankers with high pressure water caused soft explosions by igniting the residual evaporates by built up charge.

This did sink minimum 3 medium sized tankers in harbors during cleaning.

You may remember the ill-fated TWA 800 flight that came down over New York with fuel tanks burst from internal overpressure. This seems to happen rarely when the tanks are near empty and heavy fuel movements at flight maneuvers causes droplets to be formed where the connecting pipes go into the fuel-tanks. New aircraft are now built with nitrogen above the fuel - no longer air!

There are different mechanisms of charge buildup:

a. A particle or droplet is stripped off a charged surface (nozzle) and carries away some charge.

b. A polar medium (water droplets) redistribute the charge near the nozzle. If the nozzle is positive then negative charge is concentrated nearer to the nozzle and negative charge away from the nozzle. If then the droplet is disrupted in two pieces one of the pieces is positive and the other negative. The negative will find its way back to the positive nozzle, the positive piece will find a way to somewhere and build up charge there. All signs inverted if the nozzle is negative.

In the fire extinguisher there may have worked another effect: particles that hit each other (and do not stick together) carry away different charges that may become separated. This is one of the mechanisms how lightnings are charged in thunderstorms.

RHABE

As mentionned, this is obviously a static discharge (dry context, charge building factors,...). Not only can static discharges be dangerous as a side effect (physical reaction of the person feeling the discharge, providing a spark in an explosive environment and so on...) but it can actually lead to third degree burns (experienced with a commercial vacuum cleaner collecting dry powder material).

If the extinguisher is UL listed, then it is tested under UL/ANSI 711: Rating and Fire Testing of Fire Extinguishers.

The letter 'C' in "1A-10BC" means the extinguishing agent does not conduct electricity. That is why there are no extinguishers with a 'C' rating only.

Very strange, the circumstances described here. Are you certain it was an 'ABC' and not an 'AB' extinguisher?

You are misunderstanding the physical effects here.

Non conducting "things" can get very highly charged with static electricity - rubber balloons, plastic combs, hair, plastic sheeting, many types of powder and dust etc etc etc.

Conducting things lose their charge as fast as it is generated.......eg. the charge is lost before it gets dangerous.

Understood?

I notice everyone seems to be discounting the V belt as a potential and think the discharge of the ABC extinguisher created the static in the dry climate. My research of potential discharges from ABC extinguishers all claim not to have any static sensitivity and that is a claim on several MSDS factoids. My experience with windup machines in cold Canadian climates (dry) indicate static on windups is a big issue.

Consideration of why the fire started on the blower may lend another clue. If the V belt was creating a large static and some flammable material were near or on the blower, could a static charge not ignite such material? If the machine was still running a new static charge would build up. When the operator used his extinguisher, he experienced the tingle of being near a static charge and then when he reached in to extinguish the fire, he was whacked by the full static discharge. Tingling or hair raising on the arms is common at 6 feet but I suspect the operator reached in much closer when he was hit. This scenario seems much more plausible than the static coming from the material discharge of the extinguisher.

It seems that if static discharges were common from ABC extinguishers in dry climates we would have heard about it long ago. That would be a serious hazard to the user of extinguishers everywhere. Sawmilleng reports it has never been an issue at this mill. And like I said, windups put out a lot of static and more so in winter. Better evidence points to the V belt as a source of static in this case. I won't say conclusively that a discharge created the static, but I will say it was not probable.

kevinm:

If this: "Sensitivity to Static Discharge: Not Applicable" is the basis of your conclusion, I take exception to your findings.

I infer from this that the powder will not self ignite due to a static discharge. Not that the powder will not induce a static charge.

Just my thoughts.

Not exactly the only reason. But the dry chemical actually forms a wet product instantly on discharge and that would be less inductive to creating static charges. Time would also be a factor for a large enough static charge to affect the operator so quickly. I think??

I have asked the National Fire Protection Association to provide a comment. They may respond directly to the thread ( I gave the URL) but if they come through me, I will pass on the information. It seems an important point ... if a large static charge can be created by extinguishers. Many extinguishers have been discharged away for the fire but on flammable material....not a good idea if that happens. Since it hasn't been an issue, I would assume the static created by discharging the extinguisher would be a moot point. It is an interesting problem and although I am seldom involved with fires I would really like a definitive answer; just in case. Lets get an answer from the horses mouth. I am not the electrical whiz nor do I have a wealth of information about fire extinguisher manufacturing.

Fair enough. I'm no expert either.

Let's hope that there is a rational explanation for this episode, and we all come to know what it is.

Cheers.

Kevinm,

Thanks for this! I didn't think about querying "these guys", but we might as well. The only problem about asking these types of guys is that they may mull it over in the back rooms with the good ole boys, run it past their lawyers, bounce it off their board, and the end result will be a non-answer. I tried this with some other guys on a pressure vessel question once and the weaselling and worming was a wonder to behold.

On another of your comments, why do to say that the dry chemical is "instantly wet" once it leaves the extinguisher? Am I missing something?

Jon.

Hi Jon

I would think that if the extinguisher contains phosphoric acid that it will react with the water in the air , even in dry/cold conditions. H3PO4 has a very high affinity for water. The gel that I see in the ABC ingredient list is likely there to try to keep it dry until used. It is corrosive on metals and does form a sticky residue. In fact I learned that you don't use them on computers or airplanes where corrosion can be an issue. Airplanes have special extinguishers to circumvent corrosion problems...I hope.

I wonder if the sawdust could be the source of the static charges?

I did ask the NFPA to respond ASAP but that could be slow. If they are reading this thread they may get a better gist of the urgency and have pride in costumer service. I once worked 12 years for the Ministry of the Environment and I can say the quality of responses varied dramatically from one officer to the other. Once I started my own business, invoices to the government were paid at a snails pace and I was informed that they would not pay late charges. After that I billed at higher rates in compensation. Tardiness does have a price especially when accountability was weak. Now retired so I can be as tardy or fast as I want except when my wife says jump.

Regards

Kevin

Lots of good suggestions and experience here! Thanks, all, for your interest and comments!

I have one more bit of information--The motor was not running by the time the fire extinguisher was discharged; therefore any static accumulation on the V-belts may have had a short time (maybe as much as 10 minutes) to dissipate. I'm not sure how fast a charge might dissipate, if much at all, in that kind of time, but thats why I'm throwing it out for you guys to contemplate.

The fact that the motor was not running also suggests that the 480V breaker was tripped so that there might not have been AC voltage present at the motor when the fire extinguisher stream hit the motor. I am not clear if the motor was fused or on a breaker so I can't say for sure if all three phases were off line.

A question for those who are talking about static buildup in fire extinguisher hoses: I understand from the discussion above that CO2 extinguishers use static-dissipating hoses but I didn't get the same idea that dry chem extinguishers also use static-dissipating hoses. Can anyone answer this question definitively?

Keep the thoughts and observations coming!!

Jon.

The static charge could hold for a long time unless it is grounded. In my experience, the static on the polyfilm rolls could be felt well past 10 minutes, albeit at less levels that was experienced as they were winding up. The small tingle would certainly be there. And these rolls had been static discharged by wands and the tinsel. I cannot say how long the blower would hold a charge, but the machine likely ran for a while after the fire started, enough to create a new static charge.

Another point: The fire started because the motor failed, not because of static discharge. A winding shorted out or something like that. In our business, a fire usually starts when a motor fails because there is a short circuit event inside the motor. This, of course, assumes the motor is an ODP (open drip-proof) with vents that allow the fire out. The inside of the motor is usually coated with tinder-dry wood dust, so we can end up with an exciting situation.

Jon.

I would think you should be using Totally Enclosed Fan Cooled motors in a wood dust environment.

But as I am more your bush fire guy than structural, I pointed the guy I regard as the expert in that area, at the thread.

His comment was;

I would have to go with the static build up in the extinguisher itself. I have seen the static when loading powder into large extinguisher tanks. And that was while sweating my butt off. And we use only Ansul Purple K, or Williams PPK. Both are top of the line products. I can't believe it was defective powder, or tampered powder.

So with that in mind; I think that reported severity of the static discharge is quite an issue. If the 'next' person is in a confined place, the risk of physical collision and injury is high.

I therefore think it would be well worth your while to run an experiment with an identical extinguisher in the same environmental conditions.

If a charge is felt building - ground the extinguisher body on the floor and see if this removes the effect.

If so - then I suggest you train the staff to use them grounded.

It should not make much difference in fire fighting terms as aiming at the base of a fire is the idea, as is, keeping below the smoke. So one is often kneeling anyway. Possibly why I've never noticed a static charge effect.

And when it is a case of getting 'down into something', grounding against something metallic or concrete, would, I think, be generally possible. Or stopping earthing and continuing.

Better they be aware and practiced, than flung back onto something pointy.

I'd think TEFC , or even "washdown" motors, but my experience is in wet process equipment.

Quite a few mills I've been to get 'washdown' when it rains

I'm not like a 'stickler' for every tiny OH&S possibility, but timber mills, particularly the 'bush mill', tend to be a place I often think; "I wonder how so many of these guys are not dead yet".

I think there are more than enough challenges without nicely drying wood flour (explosive) inside a motor case.

I figure they are like cats.

Could it have been a capacitive discharge? The extinguisher has a metal case filled with a dielectric (e.g. baking soda) and suspended in the center of the baking soda is another metal canister containing the propellant - ergo a capacitor!

When your man hit the trigger the metal pin punctured the central propellant canister and discharged the capacitor. There may have been some non-conductive residue on the pin during the initial discharge which was cleared out by the second discharge.

The source of the original charge could have been an ongoing or old ground fault or static buildup.

corelite,

Interesting idea, but the extinguishers we use are not that style; you are thinking of the type that is pressurized by puncturing a CO2 cartridge when you need to use it. We use the type that is pressurized when it is refilled with dry chemical by the supplier.

I have an extinguisher of the type you are describing in my home shop; I don't think the enclosure tank and the CO2 cylinder enclosure are electrically isolated.

I will have the extinguisher in question next week; and will call the manufacturer to see what they can tell me about static electricity issues.

Jon.

These sites might be of interest to you concerning dry chem fire extinguishers:

http://www.kidde.com/utcfs/Templates/Pages/Template-53/0,8062,pageId%3D4313%26siteId%3D384,00.html

http://www.kidde.com/utcfs/ws-384/Assets/MSDS%20ABC%20English.pdf

These would probably be of benefit to most posters. They should be read before posting theories about the subject.

Good Luck, Old Salt

I took your advice and read through all the documents/links you supplied and the best sentence in the whole was the Disclaimer at the bottom of the last link!!!!!!

THE ABOVE INFORMATION IS BELIEVED TO BE CORRECT, BUT DOES NOT PURPORT TO BE ALL INCLUSIVE AND SHALL BE USED ONLY AS A GUIDE. PYRO-CHEM SHALL NOT BE HELD LIABLE FOR ANY DAMAGE RESULTING FROM HANDLING OR FROM CONTACT WITH THE ABOVE PRODUCT.

THERE IS NO INFORMATION, TEST OR ANY OTHER REQUIREMENT WITH REGARD TO STATIC DISCHARGE..........its simply been forgotten!!!! and in a "Fire" situation where other inflammable substances may be around, completely ignoring the possible effects of the discharge on the person employing the extingguisher......

What an oversight.

I do not share your enthusiasm with regard to these links helping us further here in the slightest......they do not help at all.......

It reminds of the car maker Opel some years ago introducing plastic fuel tanks and forgetting that petrol (Gas for US Citizens) when "slopping around" in the tank would cause the tank to get a static charge on it that sparked VERY happily to the filler spout of the filling station, which is of course should be "earthed"!!!

Also (similar to this blog!) petrol running through a plastic or rubber pipe can cause large increases in static electricity.......earthing very important.....on both tank and filler.....

Add both together.......one maybe missing an earth.....

There were many cases of small explosions as the exiting petrol vapour caught fire......dry days were the worst of course!!

Even getting in/out of your car can charge your body up with high levels of static.....

Here are 2 videos of such an accident. This is about what generally happened, I only know of one person who got burned, but no deaths. But it could easily have been a whole lot worse! It was a filling station don't forget!!

http://www.youtube.com/watch?v=grQYr507r_A

http://www.youtube.com/watch?v=j1dTSuwz0R8

Here is someone not following the rules about static prevention when a petrol bowser is filling the tank station:-

http://www.youtube.com/watch?v=earLevsRRCc

Remember static prevention and handling are a complete subject on their own, there are many people around the world in well paid jobs doing just this each and every day of the year.......

Enjoy!!!

My intent in referencing the sites was not to make absolute authorities on dry chem extinguishers out of the posters, but rather to familiarize some of those that seemed to not be familiar with the contents of them or the basic properties of the chemical within them. Some of the posters seemed to be going off on tangents based on their thoughts of possibilities and not the basic properties of the material within or the basic use of a dry chem extinguisher.

No, I do not consider myself an "absolute authority" on the subject (nor any subject) but I have enough knowledge and experience with dry chem ext. to have it be part of my source of income for the past 40+ years. When your wife and kids food and shelter depends on it that is a lot of incentive to become more knowledgeable.

MSDS's are not written to be the complete source of all necessary and applicable information and research. They are written to be a readily available source of information concerning common potential problems such as: fire, personal exposure to various parts of the body and various ways of exposure, environmental problems, etc. MSDS's are written usually by someone who hasn't had much experience with the chemical but is familiar with what is necessary for someone who needs emergency information real fast either to handle a situation or to prevent a situation. Before they are approved for distribution they are usually submitted for legal approval and the sharks always temper things to prevent future problems from a legal standpoint. 'm not very familiar with other than the USA requirements and Canada. Sorry Internationals!

My enthusiasm is not enthusiasm, since trying to enlighten those who might benefit from the links.

I do not share your enthusiasm with regard to these links helping us further here in the slightest......they do not help at all.......

That is your opinion which you are entitled to. Perhaps someone else benefited from them, if so then their posting was justified.

I am very familiar with those videos whose links you posted and could post some extremely disturbing ones if I could remember where I stored them. I have been a Haz Mat responder for over 40yrs and an Instructor for the past 30yrs. Not only is "earthing" important but also its cousin "bonding" is equally important if not more important. Detailed information on it is not published in MSDS's. rather in research papers which are available in the libraries of interested companies and universities.

Good Luck, Old Salt

You picked the perfect line out of my post!!

On reflection though it may have not been quite fair as the links showed us what was not the problem, which is also a great help.

It also showed that none of the countries concerned have made any regulations with regard to static generation generally or with regard to static and humidity levels.....

So please accept my apologies if I incorrectly gave the impression that the links were of no use at all, that was simply not correct or friendly of me......

Pax?

Aw, guys, cut us some slack here! I think there is a disconnect between what some of you are thinking of when talking "sawmill" and what today's reality is! This ain't a mill that is backed up to dad's Massey-Ferguson tractor for power.

This plant is old, being built in 1970; so it isn't heated. Men were men back then. But at least it is roofed. And production rates nowadays, to survive, need to be right up there...The sawmill produces over a million board feet per day. And that isn't very good when compared to some of the higher production BC sawmills. There isn't much machinery left in the mill building that was there in 1970. One line processes logs at over 650 feet per minute; an average log is 16 feet long and the gap between logs is about 12 feet. You do the math on how many logs per shift are processed in this one line alone. And that is with stone age 1990's technology--we have fine tuned it up as best we could over the lean years since it was installed. I just love watching a tree hugger's reaction when I tell them how many seconds it takes to turn a complete log into lumber, chips and a little sawdust. (about 1.5 seconds). And a university technical guy telling us "You can't run circular saws that fast." Our response? "Come and tell that to the saws--we've been doing it for months".

Open drip motors were used when the mill was built and are slowly being phased out as they fail. But you don't just toss a 300 hp motor out 'cause you don't like the dust in it! A new one won't give you much change from a $25K bill. And for the longest time, a TEFC motor usually meant that the service factor (SF) was 1.0 . The ODP motors at the time had SF's of 1.15 . That meant an open drip motor could put out 15% more power than a similarly rated TEFC motor. They could survive the abuse they received a lot better because of this. But that seems to have changed, and it is pretty easy to find TEFC motors with SF's of 1.15 now.

Whats that? Oh, sorry!!! Rant mode, OFF.

The bottom line within all of this is the concept alluded to by some posters that is an all too normal stereotype of the wood products industry: Safety. It's a sad representation of our industry: "you can always tell an old sawmiller: he is missing at least one finger". We're trying to get past old safety practises and move towards zero accidents. It is a challenging road.

Jon.

All suggestions are good, may be right but have you checked on the worker health with a physcian he might be suffering from other sickness ( some thing affect on nervious system and resemble electrical shock).

Ok - you mean me - and - I do tend to tease And from the outset I recognised you care about your workforce, or you wouldn't be posing this. It's also good you're phasing in TEFC.

But - the tease got you to give a clearer picture of the equipment and sort of work environment this happened in. Might have been a 'bush mill' or 'fully automated, I've seen the range, so now have a better picture of the how, where, when and scale.

That grasped - what I said about duplicating, adjusting awareness, and modifying training - I stand by, for the reasons stated. And as a trainer/instructor in the field, I would be most interested if it does duplicate as an extinguisher issue, as it is a circumstance I should incorporate into the manual - we don't like injuries either.

However, should you stay around, you will find CR4 folk have a natural tendency to want to know every little thing, because often, the 'devil is in the detail'.

As MANY here have already correctly testified to, blowing a powder (high dielectric) through tubes causes a high static charge to be built up.

If the tube is not made of a conductive material AND also not connected to ground to remove the charge, this charge can build up to exceedingly dangerous levels....

This is exactly what happened here.

Also the documents posted here on dry fire extinguisher contents from around the world show definitively that no thought has ever been given to setting requirements for any static discharge effect.

Nor was any thought/requirement given to the effects of relative humidity to the static build up either....

This also fits exactly with the effects noticed by the user of the fire extinguisher.

Remember if its stuck to your shoe and it llooks like dog shit, smells like dog shit, tastes like dog shit, it probably IS Dog shit!!!!

Arguing about it further is sort of a waste of time......just clean it off and walk more carefully next time!!!

I think that we all generally agree with you. I for one agree completely.

It would appear that we have really "opened a can of worms"!

The next question is how do we attract the attention of the FE industry to this problem? (which is what we should do really...)

Maybe the regulators are an even better way to go (how?)......

What do you (all) think?

I think that the v-belt electrostatic hype is being taken too far by the advocates.

The reality is that (a) the fire extinguisher was directed to the motor which caught fire and not to the v-belt. (b) Motor was grounded and so does any of the metal pulleys directly attached.(c) there is no indication that the lobe-type blower was resting on insulators and was not channeled to floor / ground.

Siting a practical example; During transmission line construction when stringing on a set of few towers has been done a person can get knock-over strength shock by touching the conductors since particles carried along by wind are constantly rubbing the conductors over a long period of time to cause accumulative build up and the insulators provide a perfect barrier for the dissipation of that charge to ground.

Extreme electrostatic build up also occurs in thunderstorms when clouds get charged and the air acts as insulator.

The v-belt has been touching grounded metal (insulator is missing!) accordingly there should not be any appreciable electrostatic charge - Not a tingle let alone a knock over; I mean take a metal rod in hand and directly touch the v-belt, running as well as still.

The best advise I can give you is to neglects claims of the suppliers, get the contents of the Fire extinguisher verified from an independent laboratory - Practically the operator has been knocked over while standing at a distance of about six feet from the probable source of shock.

Here's some concrete testing items I'm contemplating to do to try to get to the bottom of this:

1. Have the extinguisher contents tested by an independent lab for conductivity and the prescense of foreign product, for example:fine rust particles. I would have them obtain a new sample of the same product for comparison purposes. They would also verify the condition of the inside of this particular extinguisher pressure vessel.

2. Obtain an electrostatic voltmeter and see what kind of charge will build up, if anything, upon discharging a dry chem fire extinguisher that is handheld. If there is a demonstrable, repeatable charge build-up, compare that charge build-up to what happens when discharging an extinguisher with the metal container sitting on a concrete floor. This may represent a simple procedural change to reduce shocks.

3. Check V-belt drives with the electrostatic meter to see if there is anything to this side of the question.

4. Check around the lobe blower for static buildup that we may not have been aware of.

5. Of course, the electrostatic issue may come and go with the ambient relative humidity. We may have to wait until we get a cold snap to try tests that approach the same humidity levels in the air of the incident. But tests right now with a meter should give us an idea as to which theories might be the one to look at much closer.

Can anyone suggest anything further in this checklist? Other items to check or refinements to what I am suggesting? Feel welcome to render opinions!! This has been one heck of a good discussion to date!!

Jon.

I think that is a well constructed test protocol.

Perhaps, if weather is not cooperating, try it in a cold store?

Other 'variables' that crossed my mind, on first reading, are the presence/ejection of burning dust and 'smoke conductivity', but these assume one or more phases were still in play, or a massive particle ejection, creating it's own static charge.

I.e you sometimes see 'lightening' in the smoke of a major 'dirty fire'.

I imagine replicating that in someones cold store would be unwelcome, but first step is, as you outline, to confirm or eliminate, the extinguisher as a factor.

If 'confirmed', I certainly want to know as I'm in the position to have it incorporated in training, probably world wide.

If not then, I'd suspect active phases, and be suggesting 3 phase breakers over per-phase fusing.

Just one further thought;

So more questions - how long was it cold before the event?

- was the extinguisher openly exposed, or in a warmer place?

I.e. if you go with the cold store idea, make sure the test extinguisher is at the same relative conditions.

However, with either test; put the extinguishers in those conditions for 24 hours ahead of the test.

34point5,

The temperature was dropping since Monday and this happened on Wednesday night about midnight. I can't say just how long we were at -30 but the extinguisher isn't that massive so it would follow the ambient temperature pretty quickly. The extinguishers are hung around the plant and are at ambient, so the one used would have been very thoroughly at -30C when it was used.

I certainly appreciate your interest and feedback.

Jon.

Call it; enlightened vested interest.

Were it a liquid media it would, quickly draw down to ambient (~2 hours) but powder, (I imagine, but don't know the thermal conductivity or density factors) would be 'self insulating' to an extent. So I suggested a much longer time - to allay any nitpicking on your results.

"Wednesday night about midnight" - You may need the latter category then;

Low temperature walk-in freezer cold storage warehouse - Class J, Temperature Range: -23℃~ -28℃. The storage purpose of this deep freezer cold room is for the frozen storage of ice cream and other deep frozen food etc.

Ultra low temperature walk-in freezer cold storage warehouse - Temperature Range: ≤-30℃. The storage purpose of this ultra low temperature cold room is mainly for fast frozen food, industrial laboratory test room, medical treatment, blood bank, etc.

Can anyone suggest anything further in this checklist?

Hi Jon.

First let me say that what you are describing as your plant and the capacity of it fascinated me. If I was the maker of a documentary, I would spend a few days around the plant and would find that a lot of people would have no idea about the complexities and dangers involved.

It must be a site to behold seeing all parts in synchronized action and spitting out the valuable product. And then the capacity, beyond my imagination. Wow!

Now to your checklist question. In an earlier post I was asking about what the poor fellow was wearing. I received no reply, reaction. Not by you, nor by any of the participants in this thread. That was OK with me, because it is a long shot. Now that the matter is still not resolved completely I would like to ask if you actually questioned the guy?

Not that I am going to lose sleep over it but you did ask for:

"Can anyone suggest anything further in this checklist?"

I did in #18 but due to the absurdity (?) of my request it was possibly (unscientifically) over looked. Just a simple answer would satisfy my curiosity.

I am a long time sufferer of electrostatic discharge and have come to live with it. I had to stop wearing synthetic clothes and since then it only happens very occasionally. I could (on dry days) not shake hands with people because I knew that my introduction would, well, maybe not flatten them, but have unpleasant side effects.

Just ticking off the type of clothing, in combination with other factors, would not be diligent. Like I said, I'm not going to lose sleep over it but a simple question to the bloke involved would eliminate my suspicions. If he remembers what he was wearing and what it was made of, that very day.

Two of my brothers were lumberjacks (Germoney ^(Germany), Sweden, Finland) so I guess that your guys sort of always smell the same and would wear the same clothes for a day or two. He's possibly wearing the same clothes as he did on the day it happened, when and if you ask him.

How about if I come around with a camera crew one day and make that documentary? I might win the Lotto one day (not that I buy tickets) or come to other (hard worked for) riches. What you are describing here is fascinating. I would watch it instead of Myth Busters any day. (Now that would be a challenge for them, unscientific as they are)

Keep safe and expect the unexpected. Now I am trying to tell you how to suck eggs.

Good luck and I really mean it.

I'll leave you to it, Ky.

ky,

I initially didn't think much about the clothing the fellow was wearing. I didn't talk to him directly but we will go back and ask the question. Your comment about personal issues with static electricity is also very interesting. It's almost as if individual body chemistry could have something to do with it.

Someone else in this forum also asked if the victim was sensitive to shocks as well, or had a pacemaker or similar implants. As far as I know, this was all asked and found to not be an issue.

Are you suggesting that the victim may have been carrying a big static charge around and the act of releasing the dry chem on the fire shocked himself by releasing HIS charge? An interesting conjecture, probably testable by waving the mythical electrostatic voltmeter I keep talking about around him...Have you ever checked yourself with an meter like the above? I wonder if you have trouble at airport security checks or shopping center checkout things where they beep if someone didn't pay for an item?

When you shock someone else, or ground out your static charge, do you feel it, too? My only experiences with nuisance static has been in the dry summer, getting out of the pickup to gas up after driving for a while--ZAP! I learned to present an elbow or something not too sensitive to the (grounded) gas pump!!

There are some pretty big sawmills Down Under, too. I don't think you have to go that far to see a high speed mill, but then, coming to Canada you can sample the Maple Syrup from Eastern Canada and the unforgettable BC Bud whacky tabaccy!! And, no, we don't wear snowshoes all year long! Har!! And sawmillers tend to shower a bit more these days! We sometimes DON'T smell all the same! But tour requests are welcome any time. I'd be happy to show you around.

Jon.

Thanks for the reply Jon

It happens all the time, Airports, ferries, and not only can I see it, it is audible. I had to have a special key to enter into a hotel computer system (Early eighties) where I worked and I had downed the system many times before it was found that I was the culprit.

Not me but the guys checking had a device that showed up that I was prone to static build up. I dreaded just going to the elevator (all carpet in the place) and discharge myself when I got near the metal parts. It was very annoying to say the least.

That's when I switched to wearing non synthetic clothes and leather shoes. It worked most of the time but not always. It's just something I remembered when I read about your problem.

Once I find a saw mill that has similar equipment I'll take my grandson and show him what is done with a log. I wonder who will have the larger eyes.

Just a thought, that's all, Ky.

With higher temperatures/normal humidity, you can make quite a "safe" test as the maximum charges will be a small % age of a dry day.....So its a good move I feel.

I would put a pop rivet near to the end of the pipe for the meter lead to hang on and use the cylinder as the other contact (let the "nail" stay, do not pull it fully out!).....Also run a ground lead to the cylinder for safety reasons.

I think you can risk using a person for this.

Any reading of any voltage will be an indicator of the problem being fact..... but I would not be surprised that even under these "safe" conditions you see 5 - 15,000 volts or more .....which is not a lot static wise!!! But a sure indicator.....

Is it possible that the expanding gas from the extinguisher lowered the temperature of the extinguisher stream, and the relative humidity rose, adding moisture to the stream? Long shot at -30?

That may be how it works at a normal "safely" humidity.......good point!

I don't have any answers, but here are a couple of comments that are in a direction that only AndyGermany seems to be going.

Thinking that we won't get static charges because the powder is not conductive is going against what our third grade teachers taught us. Remember silk + glass and wool + rubber for generating static charges. These items did not conduct but I have seen the bits of paper lifted, felt the shock and heard the sizzle.

We tend to need "non conductive" for static charges. A conductor will tend to conduct the charge and it often won't be electrostatic any more.

High energy physics is way over my head. Some people understand it pretty well, but there are a lot of people with me in my group.

Under the right (or wrong) conditions you can start getting corona when the instruments for the ambient field intensity are reading about 4 KV/m. Note my careful wording. I didn't say that the point that went into corona is only at 4 KV/m. I stated that the instruments responsible for monitoring ambient electric field intensity were reporting 4 KV/m. The 4 KV/m value is not very large when you consider most strong (up North) ESD ranges from 8 KV to 25 KV with distances between items of different potential of much less than 1 meter. To understand where I am going with this consider the following definition(s) of corona:

1) Ionization of surrounding atmosphere possibly leading to corona discharge, ElectroStatic Discharge (ESD) or St. Elmo's Fire.

2) Beer typically advertised with TV commercials shot at the beach.

Either definition of corona can leave you laying on the floor.

I have never actually seen St. Elmo's fire, but I bet it will conduct pretty well. Even if this was only Elmo's Spark or the Cookie Monster's Glow I wouldn't want to bet against strange things happening when a cold dry powder is in a dense flow at a rapid rate toward a highly charged Van De Graaff generator.

I laughed so hard I had tears running down my face after reading this!! You have a way with words!

And your points are well taken. Testing by measuring field strength around V-belt drives and around a discharging dry chem extinguisher will tell us a lot.

Jon.

Since long the drivers of trucks meant to carry tanked petroleum products were using metal chains; one end connected to the body of truck at the rear while the other end trailing on the ground as the truck moves on (Orignally the scientists considered it to be a driver's obsess).

About a decade back Russian scientists concluded that in journey the tyres generate static electricity and if the trailing chains to provide ground path to the truck body are not there the accumulative electrostatic buildup can cause the tanked product to ignite.

I do not agree with the the use of electrostatic meter, issues like accuracy and methodology would sprung up; V-belt is directly in contact with grounded metal and I can confidently touch it with metal in bare hands and this is my fair guess that wood workers and mechanics at the factory in question while carrying out day to day jobs would have been touching associated metal parts several times a day without any feeling of electrostatics.

I do no take low temperature as governing factor, I am ready to take a block of ice (or solid carbon) to create low temperature as well as moisture to touch v-belt; so long as the metal parts are properly grounded there would be no issues.

Your comment:-

I do no take low temperature as governing factor, I am ready to take a block of ice (or solid carbon) to create low temperature as well as moisture to touch v-belt; so long as the metal parts are properly grounded there would be no issues.

shows a lack of understanding about the interreaction between humidity and temperature.

When the temperature drops below freezing point, the water vapour in the air changes into water and then ice. The normal name for it is "Frost"!

With -30°C over several days, there is as good as no more moisture left in the air, probably under 5% RH. That is very, very dry!!!!!

Just cooling something down does not achieve these levels of humidity!!! Except maybe in a giant freezer as someone else mentions......

There is an excellent website about this at:-

http://en.wikipedia.org/wiki/Dew_point

It explains the effect in an easily understood way, also you will see this diagram and text amongst others:-

This graph shows the maximum percentage (by mass) of water vapor that can exist in air at sea level across a range of temperatures. The behavior of water vapor does not depend on the presence of other gases in air. The formation of dew would occur at the dew point even if the only gas present is water vapor.

I hope this helps you further in fully understanding the effects of temperature on humidity levels.

There is a further website here:-

http://en.wikipedia.org/wiki/Humidity

Which explains the effects of low humidity on electronics rather well.....

Nicely put Andy - I see you have acquired an OT - let me counter that with a GA

I think we are over analyzing this, but I agree that this graph explains it in a way that even I can understand. Ga Andy.

You are also most kind.

Please note that the graph shows saturated levels against temperature, not RH.......I have not bothered to convert, but will if someone needs that factor as well......just ask.

Many thanks for both the kind words and the GA.

I expect we all know exactly who really put the OT point don't we?

"Sour grapes" we call that in the UK.....

But it really is not important for me either way, (most of the people here on CR4 are exactly the same, very few "search" for GAs!).

I am also not here for the GAs, but for overall accuracy, correctness and a lot of fun, that also keeps the old grey cells working from time to time....

If a GA comes along its very, very nice, but not the "be all and end all" so to say.......

You are the next Isac Newton....

low humity and blowing wood chips. Static could travel on the dry chemical. Are the discharge pipe on the blower well grounded?

Phoenix911,

I'd have to say, "yes", not because it has been an issue that was dealt with (it typically isn't), but the piping is large and heavy enough that it has to be supported on structural steel supports. And local electrical code demands that structural steel must be all grounded.

This particular blowpipe, which is small by sawmill standards, is 6" steel pipe, schedule 10, or about 1/8" wall. it is supported overhead across the yard on steel standards, welded to conrete foundations that are loaded with rebar.

We also blow lighter material with what we call "low pressure" systems (different blowers), but it is all in steel pipe. This lighter material consists of dry planer "shavings", wood dust, and sawdust. I noted "shavings" because they aren't really the nice curly shavings as you would expect to see off a home shop planer-they're more like small sawdust particules because we don't saw a whole lot oversize in the sawmill. This material is eminently suitable for dust explosions (it is nearly bone dry) but we never have seen an explosion. And these are big systems--36" and 40" piping. Therefore, I have to conclude that the grounded metal piping does not hold a static charge for long, if at all.

The lobe blower in question is connected to the discharge piping with a rubber coupling but the blower itself is bolted to grounded structural steel.

Jon.

at the shipyard we had 12" pipe taking away shavings from cnc routers. The wood was kiln dried. So we had to pay attention to grounding. If one Spark every got to the bag house the building would disappear in a flash. Ssssooooo, we ran a ground wire throughout the inside of the 12" pipe. We cut wood, plastic and most nonferous metal.

I believe this was pretty common, even when the equipment and building was grounded.

sawmilleng-

Thought this article, although not directly relevant to the post, might be of interest to you.

http://www.hemmingfire.com/news/get_file.php3/id/232/file/IFJ+Q4+2010+p17.pdf

It is from "Industrial Fire Journal", published in Great Britain.

Good Luck, Old Salt

When I had firefighting training in the Navy (83-87), we were taught to touch the extingusher bottle to the ground when discharging. This was for both CO2 and Dry Powder extingushers. You might want to contact the Naval Safety Center about info on static build-up on fire extingushers.

Funny the scene from "Hunt For Red October" should be mentioned. I was a SAR crewman in a helicopter squadron. One of the first things we were taught was to let the rescue hoist cable touch the ground or water before touching it. You should see the spark that comes off that thing at night! I got stuck about 20 feet below the aircraft due to a hoist malfunction and we pretty much had to do what they showed in the movie to ground the cable before I came into contact with the deck.

I scanned the thread for one item that should always be done... thank you guest for pointing it out!

Portable extinguishers should be placed on the ground prior to discharge to prevent static charge build up. I'll leave analysis of this specific situation to others, but would suggest adding the "grounding rule" to your fire fighting training at the mill...