Flammable processing areas are required to have exhaust ventilation per 1910.106(e)(3)(v). But we continue to see serious errors in the ventilation design basis, specifically where the vapors are being exhausted. The OSHA standard simply states the vapors must be exhausted to a “safe location,” but this phrase is not defined nor quantified in 1910.106.
| 1910.106(e)(3)(v)(a) Areas as defined in paragraph (e)(3)(i) of this section using Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C), shall be ventilated at a rate of not less than 1 cubic foot per minute per square foot of solid floor area. This shall be accomplished by natural or mechanical ventilation with discharge or exhaust to a safe location outside of the building. Provision shall be made for introduction of makeup air in such a manner as not to short circuit the ventilation. Ventilation shall be arranged to include all floor areas or pits where flammable vapors may collect. |
So, as I love to do, I turned to the International Mechanical Code (2021) to help me define and quantify a “safe location“; as always, the IMC does not disappoint.
501.3.1 Location of exhaust outlets.
The termination point of exhaust outlets and ducts discharging to the outdoors shall be located with the following minimum distances:
1. For ducts conveying explosive or flammable vapors, fumes or dusts:
- 30 feet from property lines;
- 10 feet from operable openings into buildings;
- 6 feet from exterior walls and roofs;
- 30 feet from combustible walls and operable openings into buildings that are in the direction of the exhaust discharge;
- 10 feet above adjoining grade