Which chemical has the lowest permissible exposure limit (PEL) among the following: Hexane, Dichloromethane, Ethyl acetate, Methanol?

• A. Hexane
• B. Dichloromethane
• C. Ethyl acetate
• D. Methanol

Answer: (B)

Permissible exposure limits are set to protect workers from the health effects of inhaled solvents, and the lower the limit, the more hazardous the chemical is considered to be. Dichloromethane is one of the most hazardous among those listed because it is readily absorbed and metabolized to highly toxic products, such as phosgene, which can cause serious lung injury and other systemic effects even at very low concentrations. This combination of high acute and potential carcinogenic risk pushes regulators to impose a very strict limit—much lower than for the other solvents.

Hexane mainly carries a risk of nerve damage with long-term exposure, but its regulatory limit is higher. Methanol is also highly toxic, particularly to the nervous system and eyes, but its exposure limit is not as low as that for dichloromethane. Ethyl acetate is comparatively less toxic and has a higher allowable exposure. Because of its especially severe potential health effects at low concentrations, dichloromethane ends up with the lowest permissible exposure limit.