How 150 ft/min Applies for Exhausted Enclosures?

3/15/2021

The International Fire Code (IFC) Section 6004 for highly toxic and toxic gases states the following for exhausted enclosures:

6004.1.3(1) The average ventilation velocity at the face of the enclosure shall not be less than 200 feet per minute with not less than 150 feet per minute.

However, in the same section for gas cabinets (Section 6004.1.2(1)), the words "at any point of the access port or window" are added after "150 feet per minute."

Doe anyone know if this was an oversight by the authors of this section? Did they miss a few words in the requirement for exhausted enclosures?

I don't understand why the 150 feet per minute would be for gas cabinets but not exhausted enclosures (albeit without referencing where the 150 feet per minute measurement is to be taken). This issue is coming up at my work as we have several exhausted enclosures and gas cabinets and some of the exhausted enclosures have ports/windows which are sealed shut. Thanks in advance!

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Tony

3/17/2021 12:15:36 pm

I see what you are saying. That has to be an typo. It doesn't even make sense without the "at any point of access..." after.

I would just assume they requirements for an exhausted enclosure are the same as a gas cabinet (for that section).

Vincent

3/18/2021 06:45:37 am

One difference between the gas cabinet and exhausted enclosure is that with a gas cabinet the access port or windows is sometimes opened to access the controls inside the gas cabinet. This is normally not the case with the exhausted enclosure. If I recall correctly, the not less than 150 ft./min addresses when the gas cabinet access port or window is open.

Ritz

3/19/2021 08:37:19 am

It’s probably due to the configuration of the enclosure opening. If it’s rectangular, floor to ceiling, exhaust duct connected in the top or back, etc. the ft/min will vary at different points along the enclosure opening. If the duct is connected at the top there will be more draw at the upper portion of the enclosure opening vs lets say the opening goes clear to the floor. One may need 250ft/min at the top to get the minimum of 150 at the floor portion of the enclosure opening.

Commentary to spray booths may help explain?

2404.7.3.2 Enclosed spray booth or spray room with openings for product conveyance. For spray application operations conducted in an enclosed spray booth or spray room with openings for product conveyance, the ventilation system shall be designed, installed and maintained so that the average air velocity into the spray booth through openings is not less than 100 feet per minute (0.51 m/s).

Exceptions:

1. For fixed or automated electrostatic spray application equipment, the average air velocity into the spray booth through all openings shall be not less than 50 feet per minute (0.25 m/s).

2. Where methods are used to reduce cross drafts that can draw vapors and overspray through openings from the spray booth or spray room, the average air velocity into the spray booth or spray room shall be that necessary to capture and confine vapors and overspray to the spray booth or spray room.

vTo help keep flammable vapors in a designated spraying space and limit the amount of overspray, the code requires that the exhaust system be adequately sized to maintain an average velocity through the openings in the booth of not less than 100 feet per minute (0.51 m/s), which is the minimum velocity to capture particulate spray material. In electrostatic spray application, paint, in the form of either powdered particles or atomized liquid, is initially projected toward a conductive workpiece using normal spraying methods and is then accelerated toward the workpiece by a powerful electrostatic charge. This process is much more efficient than ordinary spray finishing, using 95 percent of sprayed paint, thus reducing overspray.

Exception 1 recognizes this efficiency by allowing the air velocity across openings to be one-half of that required for ordinary spraying.

Competing airflows (cross drafts) in a space in which a spraying operation is located can cause a “reverse air flow” that can draw vapors or overspray out of the spray booth or spray room.

Exception 2 provides a performance-oriented exhaust air velocity option where the effect of such cross drafts is reduced or eliminated.

How 150 ft/min Applies for Exhausted Enclosures?

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