"Inhalation is an exposure route of concern if drug particles are suspended in the air. Fentanyl has potentially high bioavailability (12–100%) by inhalation [14, 15]. It is highly suspected that a weaponized aerosolized containing carfentanil and remifentanil were used to subdue hostage-takers of a Moscow theater in 2002. One hundred twenty-five died as a result of this weaponized aerosolized exposure . Although an optimized airborne dispersal device is unlikely to be encountered in a local event, we considered such a scenario for respiratory protection.
"Industrial producers of fentanyl use time-weighted average occupational exposure limits (OEL-TWA) for alfentanil (1 mcg/m3), fentanyl (0.1 mcg/m3), and sufentanil (0.032 mcg/m3) to limit exposure . At the highest airborne concentration encountered by workers, an unprotected individual would require nearly 200 min of exposure to reach a dose of 100 mcg of fentanyl.
"The vapor pressure of fentanyl is very low (4.6 × 10-6 Pa) suggesting that evaporation of standing product into a gaseous phase is not a practical concern ."
Moss, M. J., Warrick, B. J., Nelson, L. S., McKay, C. A., Dubé, P. A., Gosselin, S., Palmer, R. B., & Stolbach, A. I. (2017). ACMT and AACT Position Statement: Preventing Occupational Fentanyl and Fentanyl Analog Exposure to Emergency Responders. Journal of medical toxicology : official journal of the American College of Medical Toxicology, 13(4), 347–351. doi.org/10.1007/s13181-017-0628-2