Ventilation of Class 1 Division 1 area

[ontheqt]

We have a design that seems solid but have come up against this problem with the exhaust fans that are installed. The space is ventilated at 12 air changes per hour, exhaust is ducted high and low within the space, make up air is 10% less to create a negitive, system is controlled low ventilation rate (about 8 AC) occupied and high (12 AC) on gas detection. Here is the issue:

Exhaust fans are sidewall mounted, outdoor spun aluminum with motor out of the air stream. Electical contractor will not hook up the fan as he can see the motor is not rated for class 1 div one area like all of the other electrical on the inside of the building.

Question #1:

If the motor is out of the air stream are we good?

Question #2:

If there is a clearance rule from the discharge of the fan what is it?

thx!!

 

[RJonTilt]

If the motor is not in the air stream you are good provided the fan is spark proof. A methane system must have spark free construction.

 

[ontheqt]

We are spark proof, aluminum and the drive (belt, pully an bearing) is out of the air stream too.

To elaborate on my second question, when I ask about clearance I mean from the discharge of the fan to the motor. Is there a clearance from an opening in the classified room to non classificed electrical, in our case the opening being the discharge of the fan??

thx!

 

[KiwiMace]

Yes there is. I remember moving a door to get away from an HVAC unit on a hazardous building a couple of years ago. Sorry I can't remember the code or the distance, but I do recall considering supporting the duct, so it must have been a good few feet.

 

[RJonTilt]

Well, that could be complicated.

What is the dilution factor of the discharge?
What is ther velocity of thr discharge?
What will happen if the belt breaks?
Do you have FM aproval to the space?

Every situation has special issues.

In general, if the unit has proper velocity it will dilute the gases to a level below the LEL. ASHRAE has a whole chapter on this issue.

All exhaust must be far away from intakes/fresh air vents and the min height of discharge is in the mech. code. The other cases are covered in ASHRAE.

 

[ontheqt]

I hear what your saying about all the perameters that come into play. Seriously, I thought it was would be a straight forward look up and quote out of the electrical code...... Any mechE guys with EE buddies out there??

 

[DRWeig]

ontheqt,

I'm actually an EE with some experience in classifying hazardous areas. I haven't run across this problem before, though.

In order to classify the area, we'd need to know what the hazardous substance is, where are the sources of leakage, etc..., along with a good plan view and elevation of the building. Classification isn't covered in the NEC, but there are recommended practices from ISA. It's number TR12.24.01, or IEC 60079.

You might try posting as much detail as possible about the building, its contents, etc... Also, I'd suggest you red-flag this post and re-try in the Electric Power & Transmission & Distribution forum (link below). Lots of experienced EEs there, perhaps one has run across this before.

Note, however, that it will be really hard to get anyone to commit to an answer without physically seeing the space. Best bet is always to find a local EE with experience classifying areas.

Good on ya,

Goober Dave

http://www.eng-tips.com/threadminder.cfm?pid=238

 

[RJonTilt]

Thw whole purpose of moving the fan out the classified area was to allow the use of the other that class I div I electrical equipment.

I have install several of these. Electrical classification is based upon the concentration of the explosive gas, if you are removed from the area and the dilution of the gases are below the LEL I really think you will not have an issue, look into NFPA it will explain it in detail.

 

[sdtobin]

The motor needs to be outside the air stream and outside the classified area. Then you are good.

Usually 10 feet.