Class I, Division 1 - Explosion Proof Devices

[brucewilson]

I need help determining whether explosive proff devices will be required in our wastewater treatment plant. We have a 283,000 gallon areation basin (aerobic extended aeration plant)enclosed within a 122,000 cubic foot building. We have an air handling unit that purges the building 4 times per hour. How do you determine whether the lower explosion limit for methane gas is exceeded. I'd like to stay away from the cost of explosion-proof devices, if possible.

 

[pwhite]

Re: Class I, Division 1 - Explosion Proof Devices

this should have been already defined by the firm designing the process. you may want to contact the local AHJ, but i would get a pe to look at it.

 

[s.d. cronk]

Re: Class I, Division 1 - Explosion Proof Devices

could not agree more, absolutely should be deterimined by the designer and then reviewed for compliance by the local AHJ.

 

[brucewilson]

Re: Class I, Division 1 - Explosion Proof Devices

PE design firm apparently assumed that since this is a sewage plant project, must be class I, div I. I came in after the fact. PE refuses to due calculations or research. I doubt another PE would design differently, with the first PE claiming Class I, Div I. Any other thoughts. State electrical inspectors office just relies on the stamped drawings.

 

[ron]

Re: Class I, Division 1 - Explosion Proof Devices

You will not find someone to state that a building with methane gas is not that type of hazardous location (Class 1 Div 1). Too much liability. Easier to CYA, and spec Class 1 Div 1.
Are you an owners rep. or the contractor chalanging the design.

 

[brucewilson]

Re: Class I, Division 1 - Explosion Proof Devices

I work for the owner - a small, rural municipality with limited funds. The plant has been operated for the past 28 years, as is, except fo the new air handling unit. The installation of the MAU, new blowers and pumps is what is causing the electrical upgrade. I thought that we could get an exception since this is an aerobic plant, ie, the bacteria creating the methane gas are killed by the oxygen diffused into the system in conjunction with the new MAU purging the air. I guess not.