De-classify Class1, Div2 using LEL?

[VisitorPass]

Is it possible to de-classify a Class 1 Div 2 area by using an LEL monitor? I've never heard of this being done, nor have I found any reference to it anywhere else but, it seems to me like it would work.

I could tie the alarm contact from the LEL to a shunt-trip-breaker to cut power to everything in the area (except the LEL monitor of course, which would be wired for Class 1 Div 1).

Is there precedence for doing something like this? My application is a bottle filling line, the flammable element is acetone.

 

[charlie b]

What is an LEL monitor?

 

[Terrynistler]

lower explosive limit

 

[VisitorPass]

LEL = Low Explosion Limit

Basically, it's the minimum concentration of gas needed for combustion. An LEL monitor is just a simple analyzer to detect the concentration of the gas.

More... http://en.wikipedia.org/wiki/Explosive_limit

 

[rbalex]

LEL = Lower Explosive Limit

It is a recognized protection technique under “Combustible Gas Detection System” with certain very specific conditions. See 500.7(K).

Edit Add: The process you have described is not one of the "very specific conditions."

 

[VisitorPass]

Thank you, that's exactly what I was looking for... I guess I just never put 2 and 2 together before (my head and section 500.7).

 

[megloff11x]

I've used fume sensors in machines before but I'm not sure how they jibe with the current code. They would cut power when they detected fumes through the usual contactor scheme.

hazardous locations are tough. The gas stations seem to have the edge because there's enough volume to justify the testing hoops. Everyone else pays...

Matt

 

[rbalex]

I've used fume sensors in machines before but I'm not sure how they jibe with the current code. They would cut power when they detected fumes through the usual contactor scheme.

hazardous locations are tough. The gas stations seem to have the edge because there's enough volume to justify the testing hoops. Everyone else pays...

Matt

Combustible Gas Detection Systems were not recognized as a protection technique before the 2002 NEC. Even now they have limited application.

Edit - corrected NEC edition reference (2002 rather than 2005)

 

[megloff11x]

Combustible Gas Detection Systems were not recognized as a protection technique before the 2002 NEC. Even now they have limited application.

Edit - corrected NEC edition reference (2002 rather than 2005)

This doesn't surprise me. They were installed on machinery that was approved. There were other systems in place as well. To me they were "Fred Flintstone brakes" in that if the real brakes failed, they weren't going to save you either.

Matt