Waste Anesthetic Gases

I. Introduction

Waste anesthetic gases (WAGs) can be produced when anesthetic gas and vapors leak into the surrounding room during medical or research procedures. Waste anesthetic gases can create health effects to humans. MSU researchers and clinicians must be aware of the potential risks of WAGs and take appropriate precautions to reduce potential exposures to employees and students.

II. Symptoms of Exposure

The National Institute for Occupational Safety and Health (NIOSH) (2007) states that “exposure to high concentrations of waste anesthetic gases - even for a short time - may cause the following health effects: headache, irritability, fatigue, nausea, drowsiness, difficulties with judgment and coordination, liver and kidney disease.

NIOSH (2007) continues: “Although some studies report no adverse health effects from long-term exposure to low concentrations of waste anesthetic gases, several studies have linked such exposure to miscarriages, genetic damage, and cancer among operating-room workers. Studies have also reported miscarriages in the spouses of exposed workers and birth defects in their offspring.”

NIOSH later reports that “Some studies have documented adverse health effects (e.g., headaches, fatigue, irritability, birth defects, miscarriages, liver and kidney disease, cancer) from excessive exposure to anesthetic gases. These health effects were mainly noted for older anesthetics (e.g., trichloroethylene, methoxyfluorane) that are no longer commonly in use.  Studies are inconclusive on the potential health effects from occupational exposure to some of the newer anesthetics, such as isoflurane.

III. Sources of Exposure

MSU researchers, clinicians and students can be exposed to WAGs by:

  1. Filling refillable vaporizers
  2. When initially connecting the anesthesia system to the scavenging system
  3. Gases leaking from around an anesthesia mask or endotracheal tube
  4. Leaks in the anesthesia system, including tubing, seals and gaskets
  5. Inadequate system flushing at the end of a procedure
  6. Non-working or poorly functioning gas scavenging systems
  7. Opening the induction chambers
  8. Attending to animals in the recovery room
  9. Leakage from any tubing, seals, and gaskets

IV. Exposure Limits

A safe human exposure concentration for any halogenated anesthetic agent is less than 50 parts per million (ppm) threshold limit value (TLV), or 25 ppm of nitrous oxide over an 8-hour time weighted average (TWA).

When nitrous oxide is used in combination with halogenated gas, control of nitrous oxide to 25 ppm during anesthesia should limit concentrations of the halogenated gases to less than 0.5ppm. Charcoal filters/canisters will not work with nitrous oxide. Active scavenging is required.

V. Engineering Controls

General building ventilation systems cannot not be relied upon to control WAGs. The following engineering controls should be used to control human exposure – preference in this order:

  1. A chemical fume hood or certified Class II Type B1 (thimble ducted) or Class II Type B2 (hard-ducted) biosafety cabinet.
  2. Snorkel exhaust, or backdraft or downdraft table.
  3. Active scavenging device such as a nose cone, intubation, house vacuum.
  4. Passive scavenging only when the above engineering controls are not feasible.

VI. Work Practice Controls

The following are recommended work practices for reducing human exposure to Waste Anesthetic Gases: 

  • Avoid turning on N2O or a vaporizer until the circuit is connected to the animal. Switch off the N2O and vaporizer when not in use. Maintain oxygen flow until the scavenging system is flushed.
  • Select the optimal size tracheal tube for the animal and make sure the cuff, if present, is adequately inflated. Adequacy of cuff inflation may be evaluated by delivering a positive-pressure breath while the adjustable pressure limiting (“pop-off “) valve is closed and listening for a leak originating from around the tracheal tube cuff.
  • Occlude the Y-piece if the breathing circuit must be disconnected during surgery.
  • Once anesthesia is discontinued, empty the breathing bag into the scavenging system rather than into the room. Releasing anesthetic gases into the room could significantly increase the overall waste gas concentration within the room.
  • At the end of the procedure, continue to administer anesthetic gases/agents as long as clinically necessary, using high oxygen flow rates through the breathing circuit to wash the anesthetic gases out of the system and the animal. This allows exhaled anesthetic gases to be collected by the scavenging system.
  • It is possible to close an anesthetic circle and reduce fresh-gas flow rates. In a circle system where oxygen is the only carrier gas, the amount of fresh gas flowing to the animal should be adjusted to closely match the animal's metabolic oxygen requirement.
  • Select masks to suit various sizes and species of animals. When a mask is used for induction or maintenance of anesthesia, use a mask that properly fits the contour of the animal's face to minimize gas leakage. Minimize the time of mask anesthesia to reduce waste.
  • Use a box for induction of anesthesia in small, uncooperative animals. As with the mask technique, the induction box method requires high gas-flow rates, with substantial anesthetic spillage. Methods to minimize this spillage include tight seals on the box and placement of the box near the ventilation port of a well-ventilated room. The box can also be connected to an anesthetic gas-scavenging system to evacuate the gases in the box prior to removing the animal.
  • Make certain that the reservoir bag, used to store excess anesthetic waste gas until the vacuum system can remove it, is adequate to contain all scavenged gas. This reservoir bag is especially designed to connect to anesthetic gas-specific fittings.
  • When using a charcoal canister for passive scavenging:
    • Record the following:
      • Initial weight
      • Dates of use
      • Weight of canister before each use
    • Dispose of the canister through EHS when the total increase is close to the manufacturer specified limits
    • Use the canister in an upright position
    • Ensure that the holes on the top or bottom are not blocked. Blocked holes can prevent adequate air flow 

VII. Maintenance and Repair of Anesthetic Machines

MSU researchers and clinicians should not attempt to repair malfunctioning anesthetic machines. The designated and qualified employee or certified contractor should perform routine maintenance program to check for and fix leaking equipment and to assure that ventilation requirements are met.

VIII. Air Monitoring

Users must contact MSU EHS for air monitoring and evaluation if they suspect human exposure to WAGs.

Air monitoring will be performed on both worst case and routine exposures for each job class.

Sample results of the air monitoring along with any necessary exposure reduction measures will be reported to the supervisor and also shared with the monitored worker(s).

IX. Medical Surveillance

Acute health symptoms: MSU researchers, clinicians or students with acute health symptoms of WAG exposure should call 911 immediately for assistance.

Chronic health symptoms: MSU researcher, clinicians or employee with symptoms of possible over-exposures to WAGs should contact EHS and the University Occupational Health Physician for a clinical consultation. 

X. Personal Protective Equipment

When filling the vaporizer, wear chemical resistant gloves (not latex), safety glasses and an apron or lab coat. 

XI. Training

Supervisors are responsible to assure that workers who may be potentially exposed to waste anesthetic gases are trained to recognize, understand and reduce health and safety risks of exposure to WAGs. This training should include all of the contents of this document.

XII. Waste Disposal

For dry, empty anesthetic gas containers that are glass, deface the label and dispose in the broken glass box.

Expired or unwanted anesthetic gas containers and used charcoal canisters must be disposed of as hazardous waste; place the container in a ziplock bag and request a hazardous waste pickup via the MSU EHS website.

XIII. Resources

OSHA: Anesthetic Gases: Guidelines for Workplace Exposures


NIOSH 2007: Waste Anesthetic Gases–Occupational Hazards in Hospitals


NIOSH 2017: Reproductive Health and the Workplace: Anesthetic Gases