Why We Consider the NIOSH-Proposed Safety Limits for Diacetyl and Acetyl Propionyl Appropriate in the Risk Assessment of Electronic Cigarette Liquid Use: A Response to Hubbs et al. Visit link: Why We Consider the NIOSH-Proposed Safety Limits for Diacetyl and Acetyl Propionyl Appropriate in the Risk Assessment of Electronic Cigarette Liquid Use: A Response to Hubbs et al.