LEL Detection vs Area Classification
LEL Detection vs Area Classification
(OP)
Currently, we have area classification extending 10 ft away from three open top vessels (Class I, Div II), with a 3ft bubble around the openings and drains (Class I, Div I). These are interior tanks with point ventilation around the top (for adding dry material), and the building has excellent floor ventilation as well.
The plant wants to decrease the Class I, Div II area to 5 ft around the vessel (instead of 10ft). They measured all around the vessel, and even inside, at different times in the process with an LEL detector, and it never increased above 3%.
How is it explained that it is the possibility that hazardous vapors may be present so the LEL detector is not a sufficient enough test? Or is the LEL test sufficient to reduce the area classification boundary?
The plant wants to decrease the Class I, Div II area to 5 ft around the vessel (instead of 10ft). They measured all around the vessel, and even inside, at different times in the process with an LEL detector, and it never increased above 3%.
How is it explained that it is the possibility that hazardous vapors may be present so the LEL detector is not a sufficient enough test? Or is the LEL test sufficient to reduce the area classification boundary?





RE: LEL Detection vs Area Classification
To the best of my knowledge 10 ft and 5 ft and others are recommendation depending on factors: severity, hazardous material (Gas, benzene, propane, etc..), density, wind effect, and location
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RE: LEL Detection vs Area Classification
RE: LEL Detection vs Area Classification
What installation differences are considered for the area between the five and 10-foot radius? Typically, most electrical installations are the same. Differences may include braided flex conduit instead of sealtight.
A sniffer is not a substitute for a continueous area montor to detect hydrocarbon.
At the end of the day, if an explosion occurs, OSHA will inspect the installation.
John
RE: LEL Detection vs Area Classification
The code sets minimum boundaries; sometimes the engineer or a company standard increases them for convenience of design or for safety. For example, the military requires that the interior of pumphouses handling aviation turbine fuels be classified as Class I, Div. 1, even though the NEC is less stringent, and even though the exact same fuel does not require the same strictness if it is destined for use in a diesel engine.
Why does the company want to declassify?
Cost? The incremental cost of a 5-ft. radius of NEMA 7/9 stuff is negligible.
Perhaps they want to put some heat source in there and can't find any other real estate? It sounds as though this risks becoming a political issue.
Use your judgment, and if you are stamping the design, then you had better stick to the code as a minimum.
Wm
RE: LEL Detection vs Area Classification
John
RE: LEL Detection vs Area Classification
ISA has a good set of recommended practices. I would go by what they (or IEC) recommend.
IMHO that is.
Let us know what you decide!
Old Dave
RE: LEL Detection vs Area Classification