History of Hazardous Area Classifications

[rupej]

I sometimes encounter industrial areas that seem clearly to fall under the guidelines of a classified area (C2D2 at the least), but no equipment is designed to that specification. People in these places often resist the idea with the typical "But it's always been like this."

That had me wondering: how long has the NEC hazardous area classifications existed? How long has it actually been enforced?

From what I've seen, many places built in the 70s don't seem to be bothered by such things- so I'm guessing it was later than that?

 

[don_resqcapt19]

Class II, Division 2, really doesn't require anything more than a "dust tight" enclosure in most cases. It does not, in general, require NEMA 9 rated equipment.

 

[rupej]

Class II, Division 2, really doesn't require anything more than a "dust tight" enclosure in most cases. It does not, in general, require NEMA 9 rated equipment.

Gotcha, but I've had the same response from places that I would think should be classified Class II, Div 1 or even Class I Div 1. I was just curious about the history.

 

[kwired]

Conditions of maintenance, houskeeping, etc. can make a difference in whether presence of exact same material is deemed to make it a classified area. This especially true for materials that introduce Class 2 hazardous locations. Confined locations vs open locations can make a difference as well.

NEC in general doesn't classify a location, it does tell you what wiring methods to use once a classification is determined though.

 

[bphgravity]

It appears that rules for "Hazardous Locations" were added to the NEC in the early 1920's. The 1925 edition has a section on "Extra-Hazardous Locations" which is the genesis to the current Chapter 5, Article 500 requirements. The 1918 edition doesn't appear to address the hazard of the location where electrical work will be installed.

 

[don_resqcapt19]

Gotcha, but I've had the same response from places that I would think should be classified Class II, Div 1 or even Class I Div 1. I was just curious about the history.

Often, even in Class II, Division 1 locations you only need dust tight enclosures.

The protection method for Class II is totally different from the method for Class I.

In Class I, it is assumed that there will be ignitable concentrations of the flammable gas within the enclosure and the enclosure is designed to contain the explosion with in the enclosure and only vent gasses out of the enclosure that are below the ignition temperature of the product.

With Class II, there is no requirement to contain an explosion as the protection method is to keep the combustible dusts out of the enclosure. The biggest issue for Class II is for devices, such as motors and light fixtures, that create heat. The design for those devices in Class II areas is based on keeping the temperature well below the auto-ignition temperature of the dust.

In general, Class I, Division 1, will require explosion proof enclosures, but for other than devices that create arcs, Class I, Division 2 enclosures are not required to be explosion proof.