Hazardous Location Classification Question - Class I Div 2
Hazardous Location Classification Question - Class I Div 2
(OP)
I've gotten involved in dealing with classification of a biogas facility. In the equipment building, all of the gas is contained in piping running to some engines. Based on my recollection of the NEC, this room would require a Class I, Div 2 classification, since the gas is not normally present, but could be if there was a leak or other failure. They also have a substantial ventilation system for the building. The equipment supplier is saying that the building is "Unclassified" because the ventilation system will keep any leaking gas below a concentration that could explode. My understanding was that mechanical ventilation can reduce a Div 1 location to a Div 2, but it cannot be justification for considering the space to be unclassified.
So my thought was that it would be Class I, Div 2 regardless. BUT.... in reviewing Article 500.5, I see a third definition of Class I, Div 1 that seems to say a location that would normally be Class I, Div 2 would be considered Class 1 Div 1 if it contains electrical equipment and if a leak could directly cause this equipment to become a source of ignition.
So... based on this definition, it could be considered Class I, Div 1, but reduced to Div 2 by ventilation. In which case they will need some type of alarm if the ventilation system fails, I think.
It's been a while since I've dealt with hazardous location issue, so any feedback is appreciated.
dpc
So my thought was that it would be Class I, Div 2 regardless. BUT.... in reviewing Article 500.5, I see a third definition of Class I, Div 1 that seems to say a location that would normally be Class I, Div 2 would be considered Class 1 Div 1 if it contains electrical equipment and if a leak could directly cause this equipment to become a source of ignition.
So... based on this definition, it could be considered Class I, Div 1, but reduced to Div 2 by ventilation. In which case they will need some type of alarm if the ventilation system fails, I think.
It's been a while since I've dealt with hazardous location issue, so any feedback is appreciated.
dpc






RE: Hazardous Location Classification Question - Class I Div 2
Without detailed knowledge of the processes involved and their environment, a full area classification determination can't be made from the description given so far; however, it is certainly conceivable that the equipment supplier is correct.
RE: Hazardous Location Classification Question - Class I Div 2
Pick your poison I guess
RE: Hazardous Location Classification Question - Class I Div 2
http://12.33.72.15/pdfs/technical/practical%20guid...
RE: Hazardous Location Classification Question - Class I Div 2
I appreciate the feedback.
dpc
RE: Hazardous Location Classification Question - Class I Div 2
The famous Edith Clarke books are now available in pdf here:
http://babel.hathitrust.org/cgi/pt?id=uc1.b4164139...
RE: Hazardous Location Classification Question - Class I Div 2
This (ICoP2) and other codes are available here
http://www.esauk.org/reports_press_releases/esa_re...
Please remember that compliance with this, will not satisfy your codes, but you may find the way they arrived at their document useful.
The basic points are::
Full document is to be studied and assessed by a Competent Person. The following is a bullet point summary:
The ICoP covers extraction etc as well as power generation. Only the sections dealing with power generation are summarised here:
6.1 Overview of power generation
6.11 Engine enclosure
Control room to be separate from engine compartment
Cables passing through dividing walls are sealed
Ventilation inlet not to be within a Zone 2 created by other sources.
Ventilation for control room is independent of engine hall ventilation
Engine housing fitted with explosive gas detection.
6.11.4 Zoning (of engine hall) should be considered but boiler rooms are not zoned (BS 5885).
6.11.5 Ventilation – 12 changes /hour (subject to risk assessment)
6.11.6 Further Guidance
Risk is likely just after maintenance – procedures to ensure suitable ventilation at all times, including maintenance.
The other point is that if this is biogas from a digester, then please do not forget H2S - hydrogen sulphide.
Not only a poisonous gas, it desensitises the nose, so the danger is still present after the smell of rotten eggs has gone!
H2S also corrodes copper wiring!
In general, the practice in the UK is to put the generation outdoors in containers, so any leaks from external pipes etc cannot accumulate indoors.