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# How to Calculate Concentration of Vapor, Gas, Fume, Mist or Dust for LFL

## How to Calculate Concentration of Vapor, Gas, Fume, Mist or Dust for LFL

(OP)
Hey everyone,

I'm stuck on a laboratory renovation determining which code from IMC 510 (Hazardous Exhaust Systems) is applicable. Per the exception listed for labs:

"Exception: Laboratories, as defined in Section 510.1, except where the concentration listed in Item 1 are exceeded or (emphasis mine) a vapor, gas, fume, mist or dust with a health-hazard rating of 1, 2, 3, or 4 is present in concentration exceeding 1 percent of the median lethal concentration of the substance for acute inhalation toxicity."

Where Item 1 is:

"1. A flammable vapor, gas, fume, mist or dust is present in concentrations exceeding 25 percent of the lower flammability limit of the substance for the expected room temperature."

I know how to find the lower flammability limit (LFL) and I know what my expected room temperatures will be. However, I do not know how to calculate the relevant concentration of the flammable materials. I'm guessing that this calculation is within the domain of mechanical design, and that I am responsible for calculating it.

The only resources I found online to this matter are this post and maybe this post. The second link is a NFPA article regarding how to calculate the maximum allowable quantity (MAQ) of chemicals in a space (also has some good commentary on the difference between chemicals in use and chemicals in storage).

Any thoughts, advice or relevant experience is much appreciated!
Replies continue below

### RE: How to Calculate Concentration of Vapor, Gas, Fume, Mist or Dust for LFL

The LFL is based on percent by volume. So if you have a gas in air the lower flammability limit is the minimum ammount that will produce a flame if ignited. So 25% of LFL is 25% of this minimum ammount. Knowing a given mass of the gas you can calculate the volume percentage using the ideal gas equation. What is the gas and how does it get into the room?

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