woodworking shop

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matt_mackay

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Zion National Park, Utah
I'm new to the forum so thanks in advance for any help.
I'm an electrician for the national park service where we recently had a safety inspection. The inspector cited us for not having dustproof covers on receptacles in our carpenter shop. The shop is small with 1 or 2 carpenters working at a time. General woodworking tools (miter saw, hand sanders, planer) are used. Would this be considered a Class III Div 1 location. I realize this might also be decided by the AHJ, which would be me. Also I need some clarification on 503.145 as to what type receptacles would be used.
thanks again.
 
My opinion is that general woodworking tools do not create the hazard of flammable flyings that are covered in the 500 series articles. A saw mill might be a classified location, but I am not even certain about that. The issue is not so much that wood can burn, and that saw dust can also burn. The issue is the creation of an explosive atmosphere in which there is so much saw dust scattered evenly throughout the air that if it were to be ignited in one corner of the room the flame would travel rapidly from dust particle to dust particle. I don't believe that wood chips and saw dust that results from planing and sanding can get you into that degree of a flammable atmosphere. Don't throw a lit cigarette on the floor, but don't call it a hazardous space in the NEC context.
 
Basically, if the employees do not need to wear respirators (not just dust masks), the atmosphere is not dusty enough to be a classified area.
 
Class III Locations

Class III hazardous locations, according to the NEC, are areas where there are easily-ignitable fibers or flyings present, due to the types of materials being handled, stored, or processed. The fibers and flyings are not likely to be suspended in the air, but can collect around machinery or on lighting fixtures and where heat, a spark or hot metal can ignite them. Some typical Class III locations are:
Textile mills, cotton gins;
Cotton seed mills, flax processing plants; and
Plants that shape, pulverize or cut wood and create sawdust or flyings.
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the above is from OSHA

http://www.osha.gov/doc/outreachtraining/htmlfiles/hazloc.html

the bold and italics are mine, i don't think a plant is two carpenters, but judge for yourself.
 
My office is in the same building as a custom wood door manufacturer. Their only classified area is inside of their dust collection system.
 
jim dungar said:
Basically, if the employees do not need to wear respirators (not just dust masks), the atmosphere is not dusty enough to be a classified area.
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I agree with Jim. As a former Industrial Hygienist and cabinetmaker myself, before the atmosphere ever reaches its Lower Explosive Limit for sawdust, the workers will be passed out on the floor from oxygen deprivation. I run into a lot of people that get overly concerned about explosive protection in workshops, without realizing that the LEL concentration is virtually impossible to achieve (both for dust and for solvents) at the same time workers are present. Of course, settled dust is a different issue, but this applies to all environments.
 
LEL is an undefined term with respect to Classes II and III. See NFPA 499-2008, Table 4.5.2.

For Class II, only a discernible dust cloud or significant dust layer needs to be present to require a Class II classification. The material/air ratio is irrelevant. See NFPA 499 for both the definition of combustible dust and how a "significant dust layer" is determined. Group E is always Division 1. Groups F and G may have an associated Division 2; but truthfully, an explosion in that region is very hard to ignite even in the rare event that that a significant "release" should occur, because the dust will usually settle quickly.

Class III is actually more concerned with a rapid spread of fire rather than explosion because of the ease of ignition of built-up product. Although explosions can occur it takes a “perfect storm” because it is difficult to keep the materials is suspension. (A rapid fire is bad enough, of course) See Section 500.5(D) for the “root” Class III description; Section 503.1 does mention explosions, but 503.5 is a better description of the true concerns. Note Class III has no Groups, and Division 1 and 2 are virtually identical.

For a relatively small operation as described in the OP, good “housekeeping” is the real key to avoiding problems in both Classes II and III (or even classifying at all); but in large plants, with continuous operations it may prove difficult from time to time. . Review NFPA 499 carefully, It isn't particularly long and is one of the easier NFPA Standards to understand (IMO ;))
 
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Aside from fighting over what is and isn't code. What would it hurt to put the dust proof covers on the recpt.? I have found that when dealing with governmental safety inspectors it is some times less of a headache to just do it and be done with it than try to find ways to fight it. It would be different if they were talking rewiring with ridged and explosion proof devises.
 
RETRAINDAILY said:
You might read

NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities,

Chapter-7 :)
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I must confess that I was unfamiliar with NFPA 664; I appreciate you bringing it our attention. I am heartened that it fundamentally confirmed my earlier analysis.

As I often do, I encourage reading Scope statements; I do so here too. Section 1.1.2 basically limits the application of NFPA 664 to facilities 5000sqft or larger or to facilities that generate dust at 1500cuft/min or more. (That's a helluva lot).

I still wouldn't worry too much about the OP’s operation, unless they were severely prone to poor housekeeping. (A subject also addressed in NFPA 664, Chapter 11)
 
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