U.S. Department of Labor Fact Sheet No. OSHA 91-38 WASTE ANESTHETIC GASES 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. _________________________________________________________________________
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