Is this area considered hazardous area?

fandi

Senior Member
Location
Los Angeles
Hello All,
Composting toilets are used at a commercial building. All the poop goes to composting tanks in the basement. Everyday there will be a service person goes in and open the tanks. That's when hydrogen sulfide and methane come out and present in the room. Would light fixtures, conduits and all other electrical equipment have to have proper enclosures, sealing required for this area?
Thanks.
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
Professional Electrical Engineer
Short answer is yes.
Methane gas is explosive and has a vapor density of .6 which means it rises to the ceiling.
Hydrogen Sulfide gas is explosive and has a vapor density of 1.2 which means it falls to the floor.
Which means you have explosive gases rising and falling which means more area classification.
NFPA 497 has the complete method for you.
You will need area classification drawings to set the boundaries of the explosive hazard. More than likely you will need to hire a engineering firm to make the drawings and spec all the proper classified electrical equipment, conduit seals, etc.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
The initial question is whether it is Division 1 or 2. See Section 500.5(B). Read and understand the entire Section.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Recommend NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities
It is written specifically with your application in mind.
It goes onto nauseating detail about different installations and extents of classified areas.
1.8.1 NFPA 820 is based on the criteria established by Article 500 of NFPA 70 but shall not supersede of conflict with the requirements therein.
1.8.2 Once an area is classified, NFPA 70 shall be used to specify the types of equipment and the wiring methods that are required.

From personal experience, they smell bad as in - Nauseating
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
For the few I have worked (two total - which is slightly better than a statistical sample of one) used a powered vent. Non-sparking fans are available. The two I worked were not opened every day - in fact rarely, so there was no issue with required air changes - really small fan.

I did use an explosion-proof motor. However, I'm not certain one was needed.

I would highly recommend getting a copy of NFPA 820 and reading it for your self
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
Professional Electrical Engineer
Please remember that the proper ventilation is only part of the equation. Typically, this keeps the entire room from being Class I, Division 1. There will still be division 1 near the source, but proper ventilation may allow the rest of the hazard area to drop to division 2.
Don't quote me here, but I believe NFPA calls for 6 air room changes per hour. You may need a make up air unit as well to move that kind of air.
 

fandi

Senior Member
Location
Los Angeles
For the few I have worked (two total - which is slightly better than a statistical sample of one) used a powered vent. Non-sparking fans are available. The two I worked were not opened every day - in fact rarely, so there was no issue with required air changes - really small fan.

I did use an explosion-proof motor. However, I'm not certain one was needed.

I would highly recommend getting a copy of NFPA 820 and reading it for your self
Did you use explosion proof enclosure for general lighting and other electrical equipment such as receptacles in the room?
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Did you use explosion proof enclosure for general lighting and other electrical equipment such as receptacles in the room?
Ordinary area other than a few feet around the hatches. The float level switch was CI, D1 and the conduit was sealed. Power to the J-boxes for the submersible pumps, sealed at the J-box. Every thing else is ordinary.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
A WORD of CAUTION to all - until the requirement of Section 500.4(A) is fulfilled (essentially the OP title) all other answers/responses are guesswork and this thread is effectively engineering DIY.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I have no idea where this came from.
However, I feel properly chastised.

the worm
continues
to
dig
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
Professional Electrical Engineer
A WORD of CAUTION to all - until the requirement of Section 500.4(A) is fulfilled (essentially the OP title) all other answers/responses are guesswork and this thread is effectively engineering DIY.
Correct, just giving the man a few thoughts from past experiences.
Again, a real engineering firm needs to start with area classification drawings first.
Even with a "real engineering firm", there are a lot of things open to interpretation with area classification, which figure to use, etc. Ask 10 different "experts" to make your area classification drawing and you will get 10 different drawings!! I've seen it happen!
 
Last edited:

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
It was only a caution. ;)

In this particular case, I wanted to emphasize that that proper classification documentation must be established before mitigation, equipment selection, wiring methods, etc. are selected.

Several responses did offer good references (e.g., NFPA 497 and 820) that I would readily endorse. However, until someone tells me that the Electrical Area Classification has been established (and preferably properly documented) I usually only try to cite where to look for answers rather than specifically doing the engineering. I then try to confirm/deny the questioner's responses, if necessary.

I do have a fair amount of experience but recognize there are valid alternatives to the way I would do something.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
WACK - ouch (again)
Bob -
I got no clue why this incidence of DIY engineering by Mike Holt forum tripped your buttons - In particular why this incident over the other 1000 incidents of DIY engineering within the last couple of months.

But it did and you got the hammer - not me

I do have a fair amount of experience but recognize there are valid alternatives to the way I would do something.
And we all bow to your credible knowledge. I'm not being facetious - that part is true.
 

fandi

Senior Member
Location
Los Angeles
The initial question is whether it is Division 1 or 2. See Section 500.5(B). Read and understand the entire Section.
Hello Bob,
There's this phrase at the beginning of Section 500.5(B): '...in quantities sufficient to produce explosive or ignitible mixtures'. To me, we need to have a table showing threshold of each flammable gas that will cause explosion or ignitible mixtures. Where can I find such table in NEC? Without that, we can't tell the room is Class I, Div 1 or 2. It could even be unclassified room. Quantities matter.
Some more details: The room has two exhaust fans (one main, one backup). Also a gas detection and alarm system has been installed. I'm not the engineer to design the system. As a peer reviewer, I need to come up with right questions for the engineer to answer to make sure the room would not be blown up because there will be a lot of poop and the composting bins are not air tight. The explosion might not happen over night. It would take time for it to happen.
Thanks again.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Hello Bob,
There's this phrase at the beginning of Section 500.5(B): '...in quantities sufficient to produce explosive or ignitible mixtures'. To me, we need to have a table showing threshold of each flammable gas that will cause explosion or ignitible mixtures. Where can I find such table in NEC? Without that, we can't tell the room is Class I, Div 1 or 2. It could even be unclassified room. Quantities matter.
Some more details: The room has two exhaust fans (one main, one backup). Also a gas detection and alarm system has been installed. I'm not the engineer to design the system. As a peer reviewer, I need to come up with right questions for the engineer to answer to make sure the room would not be blown up because there will be a lot of poop and the composting bins are not air tight. The explosion might not happen over night. It would take time for it to happen.
Thanks again.
I have stated elsewhere that attempting to classify directly from the NEC is usually a lost cause unless the application is subject to Articles 511 to 516. Yours isn't so you need to refer to Standards listed in Section 500.4(B) IN No.2. Two relevant Standards have already been cited in this thread. NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities and NFPA 497 Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of' Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. NFPA 820 is fairly specific to your application. NFPA 497 is more general; however, it discusses relevant material for determining the volatility of various flammable gases; i.e., see its Section/Table 4.4.2
 

fandi

Senior Member
Location
Los Angeles
I have stated elsewhere that attempting to classify directly from the NEC is usually a lost cause unless the application is subject to Articles 511 to 516. Yours isn't so you need to refer to Standards listed in Section 500.4(B) IN No.2. Two relevant Standards have already been cited in this thread. NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities and NFPA 497 Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of' Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. NFPA 820 is fairly specific to your application. NFPA 497 is more general; however, it discusses relevant material for determining the volatility of various flammable gases; i.e., see its Section/Table 4.4.2
The engineer insists that this room is not a hazardous location thanks to the powered exhausted fans and the gas detection system. I don't agree with that. Also to him, the informational note is for information only, not a mandatory section. Currently in the room, all the electrical equipment is designed as regular without any hazardous location awareness in mind.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Well, he's technically right about INs not being mandatory themselves BUT he should have a clear basis for how he then meets Section 500.4(A) by ignoring them. Otherwise, he's just guessing.

He may wish to review the applicability of FedOSHA Part 1910.5(c)(1) This applies to most State OSHAs as well. It would be a good idea to review the FedOSHA General Duty Clause too. I'd also look at 1910 Subpart S App A which is a list of Standards Fed OSHA prefers. They are also nonmandatory but ignoring them without good cause is dangerous. (Both NFPA 497 and 820 are listed)

Last but not least, which Subsection of 500.7(K) - (1), (2), or (3) is being applied to the gas detection system?
 

fandi

Senior Member
Location
Los Angeles
Of course
Well, he's technically right about INs not being mandatory themselves BUT he should have a clear basis for how he then meets Section 500.4(A) by ignoring them. Otherwise, he's just guessing.

He may wish to review the applicability of FedOSHA Part 1910.5(c)(1) This applies to most State OSHAs as well. It would be a good idea to review the FedOSHA General Duty Clause too. I'd also look at 1910 Subpart S App A which is a list of Standards Fed OSHA prefers. They are also nonmandatory but ignoring them without good cause is dangerous. (Both NFPA 497 and 820 are listed)

Last but not least, which Subsection of 500.7(K) - (1), (2), or (3) is being applied to the gas detection system?
Of course INs are not mandatory in the code. No question about that. I know the engineer can opt to use NFPA820 or not but I would definitely use that if I were the designer.
500.4 (A) only applies for a location already classified as a hazardous location. Because the room is not a hazardous location according to the engineer, he ignores that section.
 
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