Massachusetts On-Site Consultation Assists With Engineering Control Method to Lower Isoflurane Exposure in a Massachusetts Animal Hospital

The Commonwealth of Massachusetts Executive Office of Labor and Workforce Development Department of Labor Standards OSHA Consultation Program

In 2021, an animal hospital that services domestic animals for wellness and sick appointments, surgeries, and dog and cat teeth cleanings reached out to Massachusetts On-Site Consultation to get assistance with their safety and health program and to improve their safety culture.

During the initial health Consultation walkthrough, the consultant found eight hazard items. The company had an outdated Hazard Communication Program, inadequate Hazard Communication training, and outdated Safety Data Sheets (SDSs). The workplace had not been assessed to determine whether hazards were present that require personal protective equipment (PPE) and employees had not been given the related PPE training. The consultant identified issues with maintenance of an eyewash system in the janitor’s closet and found that an additional eyewash system was needed in the back room of the facility where formaldehyde was being used to house animal tissue collected during surgeries. The company addressed all the hazard items by updating written programs, providing training, and performing eyewash maintenance. The company also purchased a second ANSI-complaint eyewash system for the facility’s back room.

Passive scrubber unit formerly used as an engineering control to remove the isoflurane from the air during the anesthetization of animals.
Passive scrubber unit formerly used as an engineering control to remove the isoflurane from the air during the anesthetization of animals.

The health consultant conducted personal exposure monitoring for formaldehyde and isoflurane during three surgeries. During the monitoring, the company’s passive air scrubber unit was used to remove the anesthetic waste gases from the air. The passive air scrubber was supposed to function by returning the “cleaned” air back into the room. The effectiveness of this process was a real concern.

Formaldehyde results came back below the analytical laboratory’s limit of detection. However, the consultant found two personal exposures to isoflurane that exceeded the National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) for halogenated anesthetic waste gases of 2.0 parts per million (ppm) over a one-hour time period.1 The exposures ranged from two to three times the REL.

This overexposure led to the consultant identifying five more hazard items, which included the need for elastic cartridge type respirators to be worn during all surgeries until an effective engineering control could be put into place. The company developed a Respiratory Protection Program, ensured employees were medically evaluated, and provided respiratory protection training. The health consultant offered several suggestions for dealing with overexposure to the isoflurane gas.

The veterinary clinic decided to replace the passive scrubber with an active scrubber unit that would collect and clean the air of the isoflurane exposure. The clean air would then be vented outside the building. On January 26, 2022, after the company installed the active scrubber system, Consultation returned to the clinic to complete repeated personal air sampling during three spays and one lumpectomy. The sampling results indicated that exposures had decreased from 5.6 ppm to 1.4 ppm, which is below the NIOSH REL of 2.0 ppm.  The isoflurane exposure was also measured in a different area of the clinic and resulted in levels below the laboratory’s limit of detection.

The OSHA On-Site Consultation Program offers no-cost and confidential occupational safety and health services to small and medium-sized businesses in all 50 states, the District of Columbia, and several U.S. territories, with priority given to high-hazard worksites. Consultants from state agencies or universities work with employers to identify workplace hazards and how to fix them, provide advice for compliance with OSHA standards, train and educate workers, and assist in establishing and improving safety and health programs. On-Site Consultation services are separate from OSHA enforcement efforts and do not result in penalties or citations. To locate the OSHA On-Site Consultation program nearest you, call 1-800-321-OSHA (6742) or visit

1 When NIOSH established its REL for halogenated anesthetic gases, it did not include isoflurane because isoflurane only became available after the REL was issued. However, NIOSH applies this REL to isoflurane. See NIOSH Health Hazard Evaluation (HHE) Report No. 2017-0077-3336 (March 2019).