Converting a biological vent hood to intrinsically safe

[ourious78]

Our company would like to buy a vent hood, (we found one that is surplus with all the specifications for air flow, lighting, etc.. however, it is not intrinsically safe) Is this just a change of the motor or just the wiring or both. We will be using solvents for vulcanizing in it and I would like to know A) Is this possible
B) Is this cost effective
C) Any advice you might have.

TIA

Josh

 

[dpc]

If you're in the US, I wouldn't even consider it, if only from a liability and risk perspective.

You could probably take the necessary steps to make it intrinsically safe from a practical engineering perspective, but I doubt if you would be able to get it certified by a third-party agency.

Picture yourself in the witness stand explaining that you bought a used fume hood and modified it rather than buying a new certified hood to save a few bucks.

You could always ask your risk manager or insurance company what they think of the idea.

Depending on what accessories you have on the hood, it may be a bigger job than you imagine anyway.

 

[ScottyUK]

Highly improbable that the motor is intrinsically safe. Flameproof maybe, or Ex 'N' or Ex 'E'.

dpc has the right idea - buy a certified item. The same reasoning applies in Europe as the US; the ATEX legislation over here makes individuals responsible, not just organisations, so you find you are personally in a huge amount of legal trouble if there was an event.


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Sometimes I only open my mouth to swap feet...

 

[dpc]

Agree - the motor would have to be explosion-proof rather than intrinsically safe, I suspect.

 

[stardelta]

I agree with DPC and Scotty. Here in the UK The legislation covering this sort of application is a nightmare and I cant see it being any different elsewhere. You need to contact a consultant or a contractor experienced in this field. Explosive enviroments, gas and dust grouping, T classes, zoning and correct equipment choice can be a minefield for the inexperienced. Not only does the motor have to be suitable for the zone but also the cable glands and switchgear. Your insurance company is probably the best place to start. Tell them what you intend to do and ask them what is required. Probably easier to buy a complete new vent-hood thats already certified as being suitable for use with the solvent you use, I am sure they exist.

 

[waross]

CVanadian Electrical code, 2006 Edition.
Section 0, Object, scope, and definitions

Intrinsically safe - that any spark or thermal effect that may occur in normal use, or under any conditions of fault likely to occur in practice, is incapable of causing an ignition oif the prescribed flammable gas, vapour or dust.
I doubt that even the vibrator motor used in a cell phone could be made intrinsically safe.
Intrinsically safe circuits are very low power signal circuits.
What you want electrically is an explosion proof motor and electrical installation in the hazardous areas that is appropriate for the hazardous substances that will be used.
That covers the electrical aspects, but you are still left with the mechanical issues. If the rotating fan contacts the housing due to any type of failure, is it capable of generating sparks.
Will the friction of a rubbing fan cause a high enough temperature to ignite the hazardous substance.
I would first locate the solvents in the local code and determine the class and group.
Then look for a complete motor-fan unit that is approved for the class and group. Do the same for the lighting fixtures, switches and controls. Your codes should indicate an area around the fume hood that is considered hazardous. Any and all electrical equipment within this area must be rated for the proper class and group. Don't forget that in some cases the area around the ducting may be considered hazardous.
This is just the electrical aspects of a fume hood. The fire marshal will have regulations for the location of the ducts and the disposal of the hazardous substance.
I think that the success of your project depends on your ability to find a motor and fan combination that is acceptable at an affordable price.
I would be searching for an approved fan and motor, and I would drop in on the local fire marshal to discuss the usability of the vent hood. He may be able to give you a simple yes or no. (What is the thickness of the material? Are the seams spot welded or continously welded? What was the previous use?) These questions may be more important (expensive?) than the electrical questions.
Google "explosion proof fans"
As well as conventional fans with explosion proof motors and non-sparking blades, you will find air-motor driven fans and venturi fans. A normal motor and fan, located outside the hazardous area push fresh air through a venturi which collects and exhausts the fumes.
BTW, I once connected an exhaust hood for a large institutional kitchen. The electrical inspector passed the electrical work completely. No problems electrically. Then the building inspector condemned most of the mechanical installation for multiple code violations. The complete ducting system had to be rebuilt.
I don't want to discourage you, you may be able to meet the codes easily, but there are pitfalls. Be careful and watch your ASSets.
respectfully


When you have completed your research, submit your proposal to your company's legal department and/or the insurers.

 

[ScottyUK]

Side note: 'explosion-proof' in the US equates to 'flameproof' in the UK (and Europe I think). In IEC-land it is denoted by Ex 'D' protection.


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Sometimes I only open my mouth to swap feet...

 

[ourious78]

Thats kind of what I figured, The last place I worked at the hood (I did the exact same process this hood will be used for) Was a solid metal cabinent. Electrical and Pneumatic Connections were standard recepticals in metal boxes connected with metal conduit and fittings, the only difference was the fan (squirrel cage induction) was serate from the booth and mounted above the false ceiling. I dont know about the ductwork though. I know that we had to submit an engineering approval, electrical approval, an environmental impact study, and a industrial hygiene inspection. (Note this was on a naval base in Connecticut)