Class / Division Clarification needed 1

[ZachE]

With regards to hazardous area Class 1 Division 1 and Class 1 Division 2, I could use some clarification.

I understand that the areas are classified based on the liklihood of a hazardous environment and I understand how the areas are determined to be the appropriate Class / Divison.

I am confused about the difference in the equipment itself. Is Class 1 Division 2 Equipment any less explosion proof than Class 1 Division 1? Or is it the presence of a higher maximum surface temperature that makes the difference?

Finally, if it is only a factor of max surface temp, are there any exceptions to using class 1 division 2 equipment in a class 1 division 1 area if it can be proven that the autoignition temperature of all hazardous material that could be exposed far exceeds the maximum surface temperature of the equipment?

Any advice would save me a lot of hassle.

Thanks,
Zach

 

[rbalex]

The "quick and dirty" differences.

In Division 1 ignitable atmospheres can be present at any time so we must concern ourselves with both “regular” and “irregular” ignition sources. An “irregular” source may be a short-circuit.

For Division 2, ignitable atmospheres should not generally be present so we are concerned about “regular” ignition sources; i.e., those that could ignite an atmosphere while they were operating within their normal parameters. Commonly they are “arcing, sparking and heat producing” (ASH) sources..

If a device in Division 2 is required to be explosionproof, such as a motor starter, it is no different that that used in Division 1.

 

[ZachE]

So, In general Division 1 ignition sources have extra explosion proof measures than Division 2 sources? Or are they equally explosion proof, but the presence of a heating element (higher max surface temp) catergorizes my device as Division 2?

 

[rbalex]

Electrical area classification is a function of the ignitable material involved and the “geometry” of the system. The appropriate electrical equipment is selected as result of the determining the classification. In other words, the temperature of the equipment itself has nothing to do with whether the area classification is Division 1 or 2, only that some equipment may be permitted in Division 2 that would not be permitted in Division 1.

In Class I, Division 1, virtually everything is required to be “explosion-proof.” That’s not the complete story of course, but it takes seventeen 8-1/2 x 11 pages of #10 pica type to explain it. All the same things noted as “regular” ignition sources in Division 2 are also considered in Division 1.

Electrical equipment that is of a “heating” nature, such as light fixtures, must have a “T” rating. In absence of a “T” rating electrical equipment is assumed [/] to have a minimum temperature rise of 90C over a 40C ambient. This is a T4 rating.

If the operating temperature of the device is the concern, in both Division 1 & 2, exposed surface temperatures that exceed 80% of the auto ignition temperature of the material involved must either be enclosed in an explosion-proof housing or some other recognized protection technique must be used.

The other issue appears to be whether the Division 2 techniques may be used in Division 1 if it can be demonstrated, that the auto-ignition temperature (AIT) of the ignitable material far exceeds the maximum surface temperature of the exposed surface temperatures. The short answer is no. The long answer takes someone who knows your processes intimately.

 

[weh3]

Explosionproof is explosionproof. Explosionproof does not mean "explosion-resistant", it refers to an enclosure designed in such a way that an ignition inside the enclosure does not propagate to the outside of the enclosure.

Most equipment labeled for hazardous areas is labeled for Class I, Division 1, which means it can be used in either Div 1 or Div 2. However, you also need to consider the Group and get equipment compatible with the Group to which your substance belongs, e.g., jet fuel is in Group D.

There is some equipment that is labeled for Div 2 but not Div 1.

Some general purpose (GP) equipment can be used in Div 2 areas, e.g., induction motors, provided it is not spark producing and the surface temperature will not exceed 80% of the autoignition temp (in deg C) of your substance.

Generally, specify equipment for the Class, Division, Group, and autoignition temp of the environment.

William