How do I estimate the risk level of inhaling a certain level of formaldehyde in the air?

I looked up the EPA's assessment, and they list this summary report in their IRIS database. (By risk, do they mean the risk of developing cancer, after a lifetime of exposure at that level? Risk of death? How would I tell?) In Section II.C, it lists "Inhalation Unit Risk — 1.3E-5 per (ug/cu.m)" as the estimated cancer risk.

OSHA limits workers' exposure to an average of 0.75 ppm.

I'm trying to calculate the risk level that corresponds to, based on the model in the EPA report. If I understand correctly, I first have to convert 0.75 ppm to ug/cu.m. Wikipedia lists a formula for this conversion. It appears the molecular mass of formaldehyde is about 30 g/mol, so at an ambient temperature of 72° F (22° C), 0.75 ppm apparently corresponds to 0.75 * 30 / (0.082 * 295) = 0.93 mg/m³, or equivalently, 930 ug/m³. With the risk model listed above, this appears to correspond to a risk of 0.012.

So, if I understand everything correctly, it appears this model predicts a 1% risk of developing cancer over your lifetime, if exposed to formaldehyde at the OSHA's safe level continuously. Did I do this calculation correctly? Is that the correct interpretation? This seems like a non-trivial risk level to accept, so I wonder if I'm interpreting everything correctly.


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