Class 1 Div 1 Group D..venting of enclosure

Ok so the jobs complete..execept for one thing.

The envoroment is corrosive (hydrogen sulfied, I was previously enlightend to this by Tom Jenkins..Thanks again). So I'm trying to recomend to the owner to somehow pressurize the enclosures with clean air. The have air service on site. I know that we'll need a scrubber, dryer, regulator, and pressure relief. So my question is what type of air line fixture can we install from the air line into the cabinet. Im presuming that there would be an explosion proof fitting of some type to do this with. I dont think it would be approperate to just run an air line into the cabnet without some type of check valve and flame arrestor that would be designed for this prupose.

Anybody know what I'm talking about???

Thanks in advance.. Mike.

I don't know about any explosion proof valves for pressurizing the enclosure.

It seems that a Type-X purging system like Bebco's 2000 series may be appropriate. That way the enclosure is protected by the pressurization system instead of explosion proof fittings. If you are going to pressurize the enclosure anyway, that may be the way to go.

They also have the EPV Enclosure Protection Vents with spark arrestors.

If you need more details about how this works, I will be glad to help.

-Phil

I do not have much idea of what you are really saying, but are you looking at suggesting something like this ?

regards
Sherine T.

Mike,

Are you asking what to put on the air line side to prevent combustible gas migration up thru the air line in the event the compressor stops? Or are you looking to do purged / pressurized enclosure (X,Y or Z) or just an XP box w/ a clean air purge.

Check out these guys for info, they might be able to answer your question:

http://www.bebcoeps.com/

Bob,

Actually I'm not entirely sure what I looking for. I understand that Adalet makes a flame arrestor fitting that will prevent hot gasses from excaping back into the air line in the event of combustion within the cabinet. I've contacted them but their out to "lunch". Adalet's web site is kinda short on detals.

The idea is to simply provide a clean air line into the cabnet that will provide about 2-4 lbs static pressure inside the enclosure to prevent the hydrogen sulfied from getting at the controller. I think I have everything worked out execept for the interface to the enclosure. this fitting might do it. Well see.

thanks. Mike.

PhilRey said:

That way the enclosure is protected by the pressurization system instead of explosion proof fittings. -Phil

Click to expand...

I may have misread what your trying to say, but you are still going to need all the correct fittings in a class 1 div 1 enviroment.

Mike,
We have a pretty good set up, but I don't have the info on the topp of my head, I'm not a work and won't be there until monday, if you haven't found anything by then I'll post what we have.

Martin,
Actually no special explosion proof fittings are required to tube-in the air supply from a Type-X, Y, or Z pressurization system. With the use of such a system, the area inside the enclosure is rendered non-hazardous and suitable for general purpose equipment. There's nothing inside the enclosure to ignite.

That's one of the nice things about a purging system -- no explosion proof equipment ($$$$) required. I regularly purge NEMA 4X enclosures in hazardous areas.

-Phil

ElevMike, Philrey is correct on this. I have done 'many' (read this as more than a hundred) C1 D1 cabinets. All had merely a purge valve, air drier, and regulator.

Please be aware that the purge valve MUST be adjusted properly or you stand the chance of oil canning your enclosure. (No, I haven't done it, but I have come close.)

Air fittings are sealed, but counduit seal-offs are still required, don't have my code book here. I could be wrong, wouldn't be the first time.

elevmike said:

... will provide about 2-4 lbs static pressure inside the enclosure to ...

Click to expand...

Uh, think 2-4 inches of water, not pounds. That's what purge systems use, maybe less, IIRC. You don't want to create a potential bomb. Even 1 psi is a great force to deal with in any moderate size enclosure.

Take a look at http://www.expoworldwide.com for purge & enclosure pressure systems. Better yet, talk to the rep in your area.

Like PhilRey, I also do many purged, plus, XP enclosures. They are two different beasts.

Ahd yeah, Bebco is also good. We buy & use purge systems from them too.

Ok guys, thanks for all the informative replies. I'll take the info and links here and take a good look at everything this weekend.

Thanks again.

Mike.

H2S & cabinet purging

Mike,

H2S is nothing to mess with and you are right to be careful.
FIRST what is expected air concentration of H2S under normal conditions??
SECOND what is expected concentration in a worst case scenario??
THIRD a previous comment was to think inches water instead of PSI. GOOD POINT. You do not need to pressurize the cabinet so much as to ensure it is ventilated to keep H2S concentration low.

A rule of thumb from confined space work is 10 air changes will bring almost anything down to a safe level (KEY WORD rule of thumb) and that will be several orders of magnitude less than compbustible levels and should be in the range where you want to prevent the gas from condensing - air moisture content will be an issue also.

You MAY be able to use a blower to ventilate the cabinet with outside air and then exhaust cabinet back to the outside. Blower if mounted outside may not have to be Cl 1.

FLash arresters may be needed. It may be possible to use those installed on cabinets used to store paints / solvents.

INteresting situration. Would like to hear more and how you solve it.

Dan Bentler

Dan Bentler

Others have told me that they use a differential pressure switch (typically a Dwyer) to prove the positive pressure inside the enclosure - one side of the dp switch is vented to the outside atmosphere.

If you pursue a proof switch, be sure to confirm the sensing element's compatibility with H2S, or the presence of H2S could eat the sensor diaphragm.

Loss of positive pressure could produce a hazardous situation over time.

Dan

Wow, this thread takes me back about ten years or so.

To reiterate what has been said:

1) Inches of water column. If memory serves me correctly we used 8 inches for a 18x24x18 Nema 4 enclosure.

2) You need a differential pressure switch that is wired to cut power on loss of purge. This probably should be a C1 D1 model.

3) Sealoffs are required within 18 inches of the enclosure.

4) Unless code has changed, flame arresters should not be required.

5) You will need a purge flow valve as well.

Lastly, I am sure you are aware of this, but others who read this forum may not be so here goes...

H2S will kill you in seconds by paralyzing you. Always have a meter or other sensing device with you as well as a partner on the outside who can summon help. Thsi person should not attempt rescue by themselves.

Icky,

This must be the most expensive job of this type in our history. There are no less then 6 rescue/safety personell standing by for our two techs on the job. We've suffered a number of setbacks due to flooding of the wet well. Since all the equipment is nema 7 it's NOT water proof. Actually the "water" is raw sewage. Any, and every thing put into a garbage disposal, or tolit covers the elevator equipment when it floods, and requires another team to wash it down. After the washdown we have to open everything up again and clean it all out.

Actually the project is compleated and was sched to be inspected today, however, we were hit with another pump failure & flood last friday...back to the cleanup...again.

The other issue is that they installed a new vent system that blows outside air down into the hole. The last few weeks it was 6 degrees out. So the flooding has resulted in icing inside the fixtures etc..

Cant wait till it's over..