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OSHA Fact Sheets

01/01/1991 - Waste Anesthetic Gases

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  • Record Type: Fact Sheets
  • Subject: Waste Anesthetic Gases
  • Information Date: 01/01/1991
  • Fact Sheet: 91-38

U.S. Department of Labor
Program Highlights

Fact Sheet No. OSHA 91-38


Anesthesia is as common to medical care as is antiseptic care of wounds. However, for too long exposure to and control of waste anesthetic gases (WAGs) and vapors during surgical procedures have put health care workers in jeopardy. At any given time more than 250,000 people who work in hospitals, operating rooms, dental offices and veterinary clinics, might be exposed unnecessarily to harmful levels of WAGs.

The waste anesthetic gases and vapors of concern are nitrous oxide and halogenated agents (vapors) such as halothane, enflurane, methoxyflurane, trichloroethylene, and chloroform. The list of workers with potential for exposure to WAGs includes nurses, physicians- surgeons, obstetricians, gynecologists-operating room technicians, and recovery room personnel; dentists and veterinarians and their assistants; and other auxiliaries. Hospital emergency room personnel may also be exposed, but not on a regular basis.

OSHA, therefore, has developed technical instructions designed to give guidance for coping with exposure to WAGs. The instructions cover sampling methods, leak test procedures, medical surveillance, disposal methods, training and exposure to WAGs.

- Exposure Concentrations. No worker should be exposed to concentrations of WAGs greater than 2 parts per million (ppm) of any halogenated anesthetic agent, based on the weight of the agent collected for a 45-liter air sample by charcoal adsorption over a sampling period not to exceed one hour.

Controlled agents and their respective weights corresponding to 2 ppm are: chloroform, 9.76 mg/cu m; trichloroethylene, 10.75 mg/cu m; halothane, 16.15 mg/cu m; methoxyflurane, 13.5 mg/cu m; enflurane, 151 mg/cu m; fluroxene, 10.31 mg/cu m.

When such agents are used in combination with nitrous oxide, levels of the halogenated agents well below 2 ppm are achievable. In most situations, control of nitrous oxide to a time weighted average concentration of 25 ppm during the anesthetic administration period will result in levels of about 0.5 ppm of the halogenated agent.

The occupational exposure to nitrous oxide, when used as the sole anesthetic agent, shall be controlled so that no worker is exposed at eight-hour time weighted average (TWA) concentrations greater than 25 ppm during anesthetic administration.

A complete WAGs management program includes at the outset the application of a well designed WAGs scavenging system. Such a system will consist of a collecting device (scavenging adapter) to collect WAGs and vapors from breathing systems at the site of overflow; a ventilation system to carry WAGs from the operating room; and, a method or device for limiting both positive and negative pressure variations in the breathing circuit which may be used by the scavenging systems. Most anesthesia equipment being manufactured today includes scavenging systems.

The remainder of the WAGs management program should include work practices minimizing gas leakage, the application of a routine equipment maintenance program so that gas leaks are minimized, and periodic exposure monitoring and provision for adequate general ventilation.

- Work Practice Controls. Steps that can be taken to reduce gas leakage can include: (1) Make sure that waste gas disposal lines are connected. (2) Avoid turning on nitrous oxide or vaporizer until the circuit is connected to the patient. Switch off the nitrous oxide and vaporizer when not in use. Maintain oxygen flow until scavenging system is flushed.

- Personal Sampling. The primary method of evaluating WAG concentrations in air is by collecting a quantity of air in a sampling bag and then introducing the sample to an infrared analyzer. Sampling should be conducted based on the particular anesthetic agent in use. Nitrous oxide can be sampled by using devices such a large plastic bag pump or the Landauer nitrous oxide monitor. Halogenated compounds should be collected in charcoal tubes 107-110 using two tubes in series.

- Engineering Controls. A scavenging nasal mask consists of a compact double mask system. It must consist of a shroud large enough to capture exhausted/escaping nitrous oxide exiting from a patient's mouth. An inner mask is contained within a slightly larger outer mask and a slight vacuum is present in the space between the masks. The vacuum scavenges gases exhaled by the patient as well as any excess gas from the anesthesia machine that could leak from around the edges of the inner and outer masks. Two small hoses lead to the space between layers and are for scavenging.

- Medical Surveillance. A medical surveillance program should be made available to all employees who are subject to occupational exposure to WAGs. The program should contain:

- Comprehensive pre-placement medical and occupational histories which shall be maintained in the employees' medical records with special attention given to the outcome of pregnancies of the employee or spouse, and to the hepatic, renal and hematopoietic systems which may be affected by agents used as anesthetic gases;

- preplacement and annual physical examination of employees exposed to anesthetic gases;

- employees should be advised of the potential effects of exposure to WAGs, such as spontaneous abortions, congenital abnormalities in children, and effects on the liver and kidneys;

- the records of any abnormal outcome of pregnancies exposed to WAGs and vapors shall be documented and maintained for at least the duration of employment plus 30 years.


This is one of a series of fact sheets highlighting U.S. Department of Labor programs. It is intended as a general description only and does not carry the force of legal opinion. This information will be made available to sensory impaired individuals upon request. Voice phone: (202) 523-8151. TDD message referral phone: 1-800-326-2577.

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