Ventilation of Hazardous Area

[BronYrAur]

Anyone know the code or governing authority on ventilation for hazardous areas? The International Mechanical Code calls for 1 cfm/sqft. What about pressure control? I assume that a hazardous area should be negative. Don't know exactly what's in the room other than it is used for chemical storage. There is currently exhaust and I have been asked to look into providing makeup air. How can I quantify what needs to be done?

 

[imok2]

According to the book "HVAC, Rules of Thumb" by Arhur A. Bell JR on page 85, Ventilation Requirements, "Ventilate all hazardous locations with 2.0 CFM/sq ft of floor area or 12 air changes per/hr minimum with half the air flow supplied and exhausted high (within 6" of the ceiling or structure)and half the air flow supplied and exhausted low (within 6" of the floor)

 

[BronYrAur]

I have no problem with too much ventilation. i.e. going with 2 cfm/sqft if in fact only 1 cfm/sqft is required. But don't i need to keep this room negative to adjacent spaces? If so, how do I quantify it? Is there a percentage more of exhaust that I should have compared to my makeup air?

 

[imok2]

The purpose of ventilation is to keep the concentration of combustables at a minimum you definately don't want a negitive pressure in the room, this in my estimation would do the opposite of what your trying to accomplish,and a sure bet for trouble.
ventilation:
Sufficient air movement throughout the room or building to prevent the formation of pockets of stale air.
Sufficient fresh air supply and foul air exhaust to limit the level of air pollution from all sources in the building.

 

[ChasBean1]

I completely disagree with Imok2 regarding not wanting negative pressure in the room. It should be negative relative to surroundings to contain odors. Go about 5-10% less on the make-up air design volume.

 

[imok2]

I'm not talking about oders i'm saying that the definition of the term Haderdous is inreference to this:
The determination that areas can be classified as hazardous locations is based on the following:

The possible presence of an explosive atmosphere such as flammable gases, vapors, or liquids (Class I), combustible dusts (Class II) or ignitable fibers & flyings (Class III);
the likelihood that the explosive atmosphere is present when equipment is operating; and
the ignition-related properties of the explosive atmosphere that is present.
This approach to classifying hazardous locations is used by the United States (National Electrical Code), Canada (Canadian Electrical Code), Europe (CENELEC EN60079-10) and throughout the world (IEC 60079-10).

 

[chicopee]

Also check out OSHA federal register 1910 for reference.

 

[VEEKRISH]

I go with ChasBean1. Any hazardous area will mandate negative pressure with respect to the surroundings for containment. I will sya, go with 10% less make up as compared to extract air. That should do the trick.