503 -Class III

[charlie b]

We are having a debate in our office as to whether a specific room within our design will need to be called a Class III space. Part of our problem is that none of us have actually encountered a project that had a Class III space. So we don't have any situations to compare against our project. The basic question: what exactly constitutes fibers or flyings? Without getting into the specifics of our project (not yet, anyway), can I ask for examples of projects that did fall under Class III?

 

[mgookin]

Go back and read 500.5(D).
Does that help?

 

[jumper]

May be helpful.

Class III Locations
The third type of hazardous location is called a “Class III Location”. This classification is created
by the presence of easily ignitable fibers or flyings. Typically these fibers and flyings are not
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.

https://www.osha.gov/dte/grant_materials/fy07/sh-16615-07/haz_locations_handout.pdf

 

[GoldDigger]

Note that proper procedures to prevent the accumulation of flammable debris can remove the Class III status.

 

[charlie b]

Go back and read 500.5(D). Does that help?

Thanks. But, actually, no, because that was part of why we are debating this issue. The informational note includes clothing manufacturing plants. Our project involves creation of a new backstage work area at an opera house. It will include 20 or more industrial sewing machines in close quarters. The debate is whether that comes close enough to a clothing manufacturing plant to bring Class III into play.

 

[charlie b]

Note that proper procedures to prevent the accumulation of flammable debris can remove the Class III status.

Is that written somewhere in article 500? Not that it would be of much use to our project. I doubt that an opera company would invest much effort towards keeping the area clear of debris.

 

[mgookin]

Thanks. But, actually, no, because that was part of why we are debating this issue. The informational note includes clothing manufacturing plants. Our project involves creation of a new backstage work area at an opera house. It will include 20 or more industrial sewing machines in close quarters. The debate is whether that comes close enough to a clothing manufacturing plant to bring Class III into play.

I think it can be debated until the cows come home.

Maybe contact AHJ for the project location and see if you can get something in writing (ask them via e-mail?).

 

[GoldDigger]

Thanks. But, actually, no, because that was part of why we are debating this issue. The informational note includes clothing manufacturing plants. Our project involves creation of a new backstage work area at an opera house. It will include 20 or more industrial sewing machines in close quarters. The debate is whether that comes close enough to a clothing manufacturing plant to bring Class III into play.

The sewing machines are not likely to generate much if anything in the way of debris, but somebody will be cutting cloth too. Again, scissors do not generate much flying thread, but there could be loose threads coming from fabric edges, as well as fabric scraps on the floor.

 

[GoldDigger]

Is that written somewhere in article 500? Not that it would be of much use to our project. I doubt that an opera company would invest much effort towards keeping the area clear of debris.

Not that I know of, just by analogy to sawdust and wood chips not requiring classification is a proper dust control system is in place.

 

[charlie b]

Maybe contact AHJ for the project location and see if you can get something in writing (ask them via e-mail?).

I did that, even before I posted this thread. It generally takes the City of Seattle a few days to send a response. I haven't heard back from them yet.

 

[rbalex]

My initial response is, “Don’t worry about it; it isn’t a Class III installation.”

If an installation isn’t within the scope of Articles 511 to 516, attempting to classify from Article 500 is a good example of “This Code is not intended as a design specification or an instruction manual for untrained persons.” [Section 90.1(A)]

In over 45 years, I’ve never run into a “trained” building official with respect to classifying a location although many are quite competent with respect to the installation itself. Building officials are prone to over-classifying “just to be safe.” I’ve met a few competent insurance AHJs

Section 500.4(B) Informational Notes lists several external references that should be used to classify a location. Unfortunately, none of them deal directly with Class III. NFPA 499 now deals more or less with classifying both Class II and III.

Several Article 503 exceptions hint at the housekeeping concept Golddigger referred to; e.g., Section 503.125. Although it is more a protection technique than modifying the electrical area classification.

Until Article 506 included Zone concepts, Class II and III were pretty much separated. If you read Article 503 carefully, you will find Class III is more interested in flash fires than explosions. You will also find there is virtually no difference between Division 1 and 2 installations.