Spark Safety: Newsletter Challenge (November 2013)

C'mon, this could be a source of humor. Think of all the dumb jokes can we write about explosions. Like:

If you work at a mine, a flour mill, or a similar environment, gas station you must take extraordinary precaution not to produce any electrostatic spark inspect the tanks using a lit match. Why is this important and required by law?

Maybe admin are just checking who survived Halloween.

"Why is this important and required by law?"

Because you can't fix stupid.

Hanging on with bated breath for the "correct" answer.

I just checked the calendar and no, it is not April 1st.

Q is very specific about the type of spark. Strange.

Not really. Those environments are simply huge fuel-air bombs waiting for ignition.

True, but I had in mind from the distant past, a case where a metal on metal or metal on concrete impact ignited the bomb.

We use this property when we pulverize coal and mix it with the combustion air in power stations, except we make a stream of the mix but don't keep a large volume.

Yes, ESD can also generate that spark as easily as flint & steel.

ESD is a critical element to control under these conditions.

ESD of 15kV to 35kV can be generated in your synthetic or silk dress causing many sparks. Don't you hear spark sound when you remove some specific types cloths like woollen cloths?

Even water jet used for cleaning can generate ESD and explosion due to friction in anything that is insulating dielectric solid or liquid.

It something a farm boy has beat into his head from an early age. I was shown. A hand full of organic dust from grain or hay thrown into the air and lit with a match. Makes a spectacular flash.

Well you sure don't want to get caught in it when it goes off.

Don't remember if there is a law on a farm about it. So I'd say the law is for those folks that are dumber then a farm boy and liability issues. Cause no matter how a company beats it into a employees head some will still not get it.

An explosion caused by dust destroyed a plant in Kinston, NC;The result of dust ignition:Rubber powder.
Burning is a very fast form of oxidation.An explosion is a very fast form of burning.
Almost anything,when finely divided,will explode under the right conditions, even beach sand.
The military has used this to destroy bunkers hidden in deep caves.
First, the dust is dispersed,but not ignited.Dust can go around corners,whereas a normal explosion cannot readily turn a 90 degree angle.These bunkers were built with 90 degree bends to minimize damage from missiles,so the military had to develop a method to defeat this.The answer was the "dust bomb". After a carefully timed dispersal interval,it is ignited.
Even if you were not killed by the heat and explosion when the dust was ignited,your lungs would collapse; due first, to the bone crushing pressure and destruction of internal organs, and second,the lack of oxygen, then followed by the extreme vacuum after.
This "huff and puff" of the explosion continues through several cycles.
Bad stuff.
http://www.wral.com/news/local/story/1089950/

Any spark is important and can be a source of ignition. These areas are considered explosive invironments so the electrical items are designed to exclude dust to prevent explosions. Electrostatic is a very real additional source of ignition that needs to be watched. It is not always easily controllable. I was in a public school as a child that during a dust storm, had an explosion of dust between the roof and ceiling. It was quite spectacular. This was all natural dust (not made by man) caused a fair amount of damage, and was caused by the electrostatic energy of the wind. They found the architect's design problem and spent a while grounding metal ventilating grates. They had a few cases before, not as bad, that but after the grounding it all went away. As children, we were disappointed because we would rather be standing in the football field talking to our friends that studying.

Most of the mills that produce combustible dust that I have worked in had strict guidelines as to grounding of isolated metal, clothing restrictions, etc. Sadly we must have rules to require action because so many of us, including companies lack the common sense to do it without prompting.

Combustable dust is an explosive hazard.

Combustable Dust is a finely divided solid material that is 420 microns or less in diameter. They are composed of organic powders or solids. Nearly all organic powders are combustible, so it is important to be vigilant around any process where materials containing carbon (reactant) might be present.

Oxidizable matrials are the most dangerous of combustible dusts as they do not require oxygen to ignite. Most oxidizers are very unstable or reactive.

Combustable dust explosions are a considerable hazard. Because the primary explosion is usually contained by design, but it disturbs and releases accumulated dust into the atmosphere where it causes a secondary explosion with far more power and destructive force than the initial explosion.

In addition to the usual fire triangle of oxygen, fuel, ignition source combustible dust adds two more conditions for explosion.

1. Dispersion of dust particles in sufficient quantity and concentration.

2.Confinement of the dust cloud. Airborne dust burns more rapidly, and the confined space leads to pressure buildup resulting in extremely destructive explosions.

Think Fertilizer factory in Texas.

The law is in place because many people are unaware of the hazards of dust in the air. If more people were educated about it there would likely be a lot more explosions done on purpose by persons that cannot get their hands on actual explosives. And how could you trace such an explosion? Just about everybody has flour in their house. I was once told that a open box of flour left in a room would eventually cause an explosion. Not sure if that is true, but I am not leaving any open flour containers in my house.

In a mine there may be either inflammable gas (methane/hydrogen/hydrogen sulphide) or suspended coal dust in the air, all of which may be ignited by a spark in the right air-combustible mixture, in a mill it is usually suspended combustible powder (grain husk etc) that may be ignited by a spark (or flame). Suspended grain husk or coal dust are an explosion hazard in these work environments. Methane (CH₄) is highly explosive and may easily be ignited by an electrostatic spark, Hydrogen is even more easily ignited and requires less energy than Methane to be ignited Hydrogen Sulphide (H₂S) is also found in some mines and like Methane is a by-product of decay, it too is ignitable but does require more heat or energy to initiate combustion than do Methane or Hydrogen Suplhide. In coal mines coal dust is often suspended in the air as a result of the excavation at the face and ventilation, Hydrogen has been found to emanate from the rock face at very deep gold mines in South Africa and Canada.

"Hydrogen Sulphide (H₂S) ... does require more heat or energy to initiate combustion than ... Hydrogen Suplhide" What?

Minor bloop. Pollux missed the point of explosive limits.In other words, methane isn't always going to go bang.

Last I heard, the 'pig bang' had been resolved. Just mentioning because it's sort of topical.

There's a law against electrostatic sparks?

I took my socks off; is that enough to keep me out of jail?

There are biohazard laws, you know.

In my ignorant bliss, I probably break a dozen laws a day, and am completely unaware of it.

I'm sure if I entered a crowded elevator in my bare feet, somebody would be offended and a law would be broken.

There might be some momentary confusion about cheese...!

I wonder, if you don't ignite an electrostatic spark in the premises but bring along fire from outside - e.g. enter with a lit cigarette in your mouth - will this be against the law?

Seriously now, is an electrostatic spark more dangerous than one created by other means, e.g. friction, in terms of temperature and therefore, capability to ignite wheat dust or methane?

The friction created spark is also electrostatic, and they are all against the law.

Which is strange, because most times the static sparks are created by the dust particles themselves, rubbing against each other. Can wheat dust be arrested?

To prevent cross dressers from wearing their nylons to work.

This is a pre-caustionary measure required to prevent an explosion. Also, it is a matter maintaining a safe work environment (there is a government regulation but I'm not sure of it's #). Three items are required for an explosion, fuel, oxidizer, & ignition source e.g. dust particles from the media in high concentration being stored in a confined space, oxygen in the air, and a spark of some sort. Two of the three components, dust & oxygen, are part of the said environment and cannot be controlled very easily. Hence, eliminating any ignition source prevents the combustion conditon from being satisfied. In addition, the higher the surface area of the fuel, the faster it burns, thus causing the confined space to pressurize more quickly upon combustion.

These sites are susceptible to 'fuel-air explosions.' The combustible dust can reach saturation levels in the air where any ignition source will cause an immediate flare-up of the 'enriched fuel environment,' and if the area is enclosed in any way, the expanding heated air will react like an explosion.

Also, Mythbusters showed this off on TV, using a 55 gallon drum of non-dairy creamer, a road flare, and a compressed air cannon to blast the contents of the drum into the air. The Build Team were literally running for their lives from the advancing 'wall of fiery death' when the fireball was MUCH bigger than anticipated.

The hazards of dusts have been recognized for many decades. The electrical safety classification system identifies them as Class II, Division I or II, Groups E, F and G (NFPA 497). (See http://www.engineeringtoolbox.com/hazardous-areas-classification-d_345.html). OSHA explains the problem nicely at https://www.osha.gov/dts/shib/shib073105.html

with examples of past explosions and the five conditions needed for the explosions. Sparks are the ignition source. Housekeeping and maintenance are necessary to avoid collecting the fuel that can propagate the flame/explosion.

this is not a traffic road!

Electrostatic Sparks can trigger dust-explosions that can be extremely harmful

This non electrostatic shock environment is important due to the amount of 'fuel' in the atmosphere of the environment.

Throwing a match in a cup of flour or coal dust will result in a small surface area burn spot. The fuel is so dense, it excludes the air, preventing complete combustion from taking place.

Suspend all those flour or coal particles in the air, surrounded by oxygen, and a spark will catastrophically ignite the dust laden air in an explosive burst.

Gasoline also will not burn without oxygen. Actually, as kids, we used to do the excersize of lighting a match and sticking it in a can of gasoline. It would go out. As long as there was enough air movement so that there wasn't an explosive or flamable vapor above the gas. Kids are crazy. How did we ever survive?

It's called Natural selection.

The kids 'sane' enough to not try it grew up into adults, as well as the 'smart' kids who did it with proper ventilation to prevent fume/vapors from sitting over the gas. The kids who were both 'crazy' and 'stupid,' well... *solemnly removes had and bows his head* ...it was a tragedy, to be sure, but, and I'm not trying to sound evil or cold-hearted here, but it was probably for the benefit of society that they didn't grow up to have kids of their own.

Well, if you are an design safety, process or electrical engineer in the oil and gas and mining indsutries, this is related to the Ignition Prevention & Control (i.e. no sparking, no arching etc.) scope of work and Hazardous Area Classification.

Some relevant and common directives and codes & standards are below. Read these if you have insomnia.

- Directives (Law in Europe) = ATEX

- Codes & standards = Cenelec/IEC, Institute of Petroleum (IP15), APIs 500 and 505

The API has has classified the hazardous atmospheres into 3 categories:

- Class I = flammable gases (e.g. hydrocarbons)

- Class II = flammable dusts (e.g. coal dust from mines)

- Class III = flammable fibres (e.g. minute fibres in textile mills)

The literatures above also talked about maximum allowable surface temperatures, gas groups, enclosure types for different hazardous atmospheres and particulates.

Yes, electrostatic charges can start a dust explosion. So can a flame.

The danger is with the dispersal of fine powders of combustible materials such as coal, flour, rubber, some chemicals and many others. The fine cloud that is made ignites one particle which ignites adjacent particles which in turn do the same. This phenomenon is similar to the table full of ping pong balls loaded in mouse traps. One goes and then the whole thing goes. Although this is dangerous there is an even more dangerous and usually catastrophic situation.

The initial explosion loosens and atomizes other dust in the area to create another cloud of materials. This is a particular problem in flour mills and coal mines. Unless a good cleaning effort is done powder accumulates on beams, on top of machinery, on floors, and other mostly horizontal surfaces. When this material is dispersed by the initial fire/explosion there is an even bigger cloud of dust. This explodes almost instantaneously and creates the extreme large and destructive explosion. This was the reason for the explosion at West Pharmaceuticals Services Co. in 2003, an explosion of rubber dust particles above the ceiling tiles and in ducts.

In coal mines this is an even greater hazard. There is coal dust present from the activities within the mine plus usually the presence of methane gas. Coal dust will ignite in the same process as mentioned above. When this happens it very often ignites the methane, if it is above the LEL, and causes a second explosion. Very often during this situation survivors with talk of an initial explosion and then an even bigger one. To prevent this, mines use "rock dust' consisting of ground granite placed on dusty or potential surfaces to suppress the dust from becoming airborne. If it can't get up into the air it can't explode under the granite rock dust.

Laws are to prevent this type of incident from happening.

Good Luck, Old Salt