NIOSH Evaluates Exposure to Secondhand Cannabis Smoke in Open-Air Setting

Published July 25, 2019

A recent health hazard evaluation report published by NIOSH may be the first to examine occupational exposure to secondhand cannabis smoke in a real-world, open-air setting. NIOSH staff evaluated secondhand cannabis smoke exposure among police officers providing security for campus concert events at a university football stadium. The university that requested the health hazard evaluation was concerned about how these exposures might affect the officers’ health. Police officers’ duties included patrolling the venue on foot, bicycles, and in small vehicles. Others were assigned to locations around the stadium.

Agency investigators visited the open-air venue on two consecutive concert days in July 2018 to collect full-shift personal air samples and area air samples to test for tetrahydrocannabinol, or THC, the active ingredient in cannabis. NIOSH personnel collected pre-shift and post-shift urine samples to test for THC and two metabolites that are chemical markers of exposure to THC. Officers also had the option to complete an anonymous questionnaire to provide feedback about potential health symptoms they may have experienced while working at the concerts.

Nineteen of the 29 personal air samples and all area air samples collected had measurable amounts of THC. NIOSH collected a total of 58 urine samples and 29 blood plasma samples from officers. Small amounts of one chemical marker of THC exposure were detected in the urine of 34 percent of the participants. According to the report, these amounts would not be considered positive in a routine drug screening test. NIOSH’s findings did not detect any THC or the other chemical marker in the urine samples. THC and the two metabolites were not detected in any of the blood samples. The most common symptoms the officers reported were burning, itchy, or red eyes; dry mouth; headache; and coughing.

NIOSH’s report states that it is challenging to draw definitive conclusions about exposure and biomonitoring data collected during the evaluation due to the lack of occupational exposure limits and because the evaluation may be the first of its kind. While some officers were exposed to THC in air, NIOSH found the magnitude of the exposures to be “very low.”

NIOSH recommended that the employer encourage police officers to report to their supervisors any symptoms they believe result from exposure to secondhand cannabis smoke. The agency explains that the police department can use this information to determine whether any changes in procedures are needed. The information might also help identify trends related to health effects associated with secondhand cannabis smoke exposure. NIOSH’s report also suggests that the employer assign officers who report that they are bothered by the smoke to a work location where potential exposure is believed to be relatively low or nonexistent.

“Individuals differ in their sensitivity and tolerance to secondhand cannabis smoke exposure,” the report reads. “What may impact one person may have no effect on others.”

View the full report on NIOSH’s website (PDF).