Hazardous Location?

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PeteHJ

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We are providing electrical engineering for a two story science building at an existing school. Within the building is a prep room and in the prep room are two storage cabinets, one for acid and the other for flamable materials. From each cabinet is an exhaust duct rising to the roof and connected to an exhaust fan. Each fan is located in open air and the mechanical engineer specified explosion proof motors. We can understand the need for explosion proof motors, but not sure how the electrical connections should be made. Normally, on the roof, exposed conduit is required to be rigid steel or IMC (per specs) and the connection would be made with liquid-tite flex with a bonding jumper inside the flex.

Is the open air surrouding the exhaust fans considered Class I, Div. 2? If so, how far? and if so, will the RSC/IMC and liquit-tite flex meet the connection requirements?
 
The cabinets should be designed and installed per NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals and the electrical area classification should be documented by someone qualified to do so.

Not knowing the details is crippling; but, assuming explosionproof motors are being properly applied, odds are the location in the immediate vicinity of the "flammable materials" exhaust is Class I, Division 1 and LFMC is not acceptable. See NEC Section 501.10(A) especially 501.10(A)(2).




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Hazardous Locations

Hazardous Locations

Ok. So the first thing you need to do is figure out your group. You need to know what chemicals are in there and decide what classified group your location is. If it happens that you are in groups A or B, then there is some very special equipment that you will need to use. Groups A and B are reserved for flammable materials with very low autognition temperatures.

Next, you need to figure out your zones. Inside the cabinet would be definitely zone 0. At the point where the exhaust exits the fan would be a zone 1 area. Outside that would be a zone 2 area. Alot depends on what chemicals you have. Lighter than air gases will create a different shaped zone than heavier than air gases. Environment also plays a part. For instance, if you are group C zone 2, and your gas is heavier than air, your zone will be along the ground. If there is a trough in the ground or a hole for this gas to settle in, it can change the zone to zone 1. But I digress. Cooper Crouse-Hinds has a good deal of material and information on hazardous locations that can help you to identify your group and your zones.

If all of your wiring is in a Class 1 Div. 2 Groups C or D, you can actually use schedule 80 PVC conduit, schedule 40 RMC, liquidtight or SOOW. You need seal-offs at the wiring box of the motor and where the conduit penetrates to the non-hazardous location (within 18" of each). Class 1 Div. 1 would be very similar. If you have a controller or contactor nearby, it must be in an explosion-proof box (NEMA 7) with seal-offs at both the motor and the box unless they are less than 18" apart from each other.

In Class 1 Div. 2 areas, you are not really worried about terminations. Mainly you are worried about arcing and sparking components and/or equipment surface temperatures (check the T-codes of any equipment that you locate in a hazardous location).

If the motor for the fan is located in a Div. 2 area, you can use a TEFC motor instead of an EXP. There is a significant savings there!
 
Class 1 div 2 locations can not use PVC unless underground under 24 inches or more cover or encased in concrete or -

In industrial establishments with restricted public access where the conditions of maintenance and supervision ensure that only qualified persons service the installation and where metallic conduit does not provide sufficient corrosion resistance,
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501.10(B)

This is not likely to apply at a school.


Any enclosure with switches, contacts or other arc producing devices must be explosion proof and must have seal fitting within 18 inches. Another enclosure within 18 inches still needs a seal fitting between them. If you have an explosion within the enclosure you do not want to increase the volume of the area containing the explosion by not putting in the sealing fitting.
501.15(A)(1)

CL1 D2 can even have open ventilated motors installed. If a motor has switches, overloads or other arc producing components however it is not allowed unless it is CL1 D1, or is marked as CL1 D2. 501.125(B)
 
ezbz said:
You need seal-offs at the wiring box of the motor and where the conduit penetrates to the non-hazardous location (within 18" of each). Class 1 Div. 1 would be very similar.
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Boundary seals are permitted within 10' of either side, need not be within 18". 501.15(A)(4) and (B)(2).
 
When you see the picture in the exibit in the handbook 501.8 that shows flexible conduit at the moter it is flexible armored explosion proof rated conduit. Comes in 12,18,24 and 36 inch lengths. spendy but code compliant.
 
stew said:
When you see the picture in the exibit in the handbook 501.8 that shows flexible conduit at the moter it is flexible armored explosion proof rated conduit. Comes in 12,18,24 and 36 inch lengths. spendy but code compliant.
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Last time I bought a 3/4" x 12" it was $223.00. You don't use these if you don't have to.
 
stew said:
When you see the picture in the exibit in the handbook 501.8 that shows flexible conduit at the moter it is flexible armored explosion proof rated conduit. Comes in 12,18,24 and 36 inch lengths. spendy but code compliant.
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...and they are called "flexible couplings", as I noted earlier.
 
It may not be the actual acid fumes that are that flammable, but the reaction that may happen if it is spilled. Take for example, sulfuric acid. If sulfuric acid spills onto metal, it creates hydrogen gas. :happyyes:
 
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WorkSafe said:
It may not be the actual acid fumes that are that flammable, but the reaction that may happen if it is spilled. Take for example, sulfuric acid. If sulfuric acid spills onto metal, it creates hydrogen gas. :happyyes:
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Flammable and explosive are also two different things. In the situation where there is an exhaust fan wouldn't the question be whether there is a risk of explosive elements being built up in the fan motor and ignition a possibility when starting the fan? If the fan is already running when the explosive element is introduced in the air stream you really have nothing different than some industrial gas fired heaters what is located at the discharge of the vent is what is in jeopardy in this case.
 
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