Explosion Proof Fans

[lucaspenalva]

If i'm using a centrifugal fan to extract air frmo a battery room, and I place it above room's ceiling (thus outside explosive atmosphere), does this fan need to be explosion proof? If yes, why?

 

[berkshire]

The primary gas evolved from batteries especially if they are being charged, is Hydrogen and Oxygen. Presuming you are using Lead acid batteries.

Hydrogen will linger under the ceiling and find any holes in that ceiling, If you do not use a totally enclosed fan cooled motor, you have a good chance of a hydrogen stream finding the brushes in your motor. Think about it.

B.E.

You are judged not by what you know, but by what you can do.

 

[chicopee]

Hydrogen is an explosive gas. The main question what is the concentration of hydrogen would you expect in that room? I would try to quantify that concentration by the number of batteries being charge and determine how much hydrogen gas is released during the charging periods, and figure out the size of the room. to calculate the concentration. If it is a small enclosed room with a lot of batteries being charged, yeah I would recommend an explosion proof fan. By contrast where you may have a battery station with lets say a half dozen fork trucks connected to the chargers within a wide open space such as an indoor loading dock then you can get away with a regular fan, however, to satisfy OSHA inspectors do some calculations.

 

[willard3]

Whether you need an explosion proof fan depends upon the concentration of explosive gas (hydrogen).

 

[lukaiENG]

The codes in USA lets you comply one of 2 ways:
[ol 1]
[li]Provide 1 CFM/sf which over ventilates the space and minimizes the concentration below dangerous/explosive levels.[/li]
[li]Calculate it out along the lines of what chicopee outlines above. The ventilation rate should be designed to keep the H2 concentration below 1%.[/li]
[/ol]

The LEL for hydrogen is 4% so anything below this will not be a safety risk.
In my experience, the 1CFM/sf is overkill and you can get away with substantially less exhaust the calculation method.

back to your original question - do the fans need to be explosive proof? No, unless you are designing the system wrong.

 

[GroovyGuy]

I believe that there are a number of applicable codes that will define the requirements for ventilation in a battery room.
Q: Are you planning on using a sealed (ie VRLA) type of battery or flooded LA battery. This can have a significant impact on the amount of H2 produced, and subsequently released into the room.
A little trick that I have used before is to not use an exhaust fan to ventilate a room, but to use an inlet (ie pressurization) type of fan together with a exhaust damper. The inlet fan is located low on the wall and the exhaust damper is located high on the wall (ie near the ceiling). This implies that the inlet fan (and motor) need not be explosion-proof, altough I would recommend that a 3-phase (ie brushless) TEFC motor is preferred over a single-phase (ie brush-type) motor.
GG


"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[lukaiENG]

I agree with groovyguy's comments. NFPA, NEC, IMC & ASHRAE all have sections on battery exhaust requirements. They are all similar but have some differences. NEC for example actually requires you to assume that VRLA batteries have the same (higher) H2 evolution rate as flooded lead acid.
One commonality is that each section talks about ventilation, the word exhaust is not used. So Groovyguy's "little trick" is perfectly valid in my view. We often do the same thing, normally just to avoid providing extra fans - we just use the house ventilation system to ventilate.