ACGIH threshold limit value-time-weighted
average (TLV-TWA) refers to the time-weighted
average airborne concentration of a substance, for a normal
8-hour workday and a 40-hour workweek, to which nearly all
workers may be repeatedly exposed, day after day, without
(APL) Valve, also known as a "pop-off"
valve, is a user-adjustable valve that releases gases to the
atmosphere or a scavenging system and is intended to provide
control of the pressure in the breathing system. The volume
of gas above that needed to achieve the required patient pressure
Air is the
elastic, invisible mixture of gases (chiefly nitrogen and
oxygen) that may be used with medical equipment; also called
is equipment intended for dispensing and delivering anesthetic
gases and vapors into a breathing system.
is any of a variety of assemblies designed to administer an
is a drug that is used to reduce or abolish the sensation
of pain, e.g., halothane, enflurane, isoflurane, desflurane,
sevoflurane, and methoxyflurane.
Anesthetic agent vapor
is the gaseous phase of an anesthetic agent that is normally
a liquid at room temperature and atmospheric pressure.
is any gaseous substance, e.g., nitrous oxide, used in producing
a state of anesthesia.
is a device designed to facilitate the change of an anesthetic
from a liquid to a vapor.
is any area in a facility where an anesthetic agent or drug
is administered in the course of examination or treatment.
This includes operating rooms, delivery rooms, emergency rooms,
induction rooms, and other areas.
is a sample collected at a fixed point in the workplace. The
data from the area sample may or may not correlate with an
individual’s personal sample results due to the often
high degree of variability in exposures.
is a gas pathway in direct connection with the patient's lungs,
through which gas flow occurs at respiratory pressures, and
into which a gas mixture of controlled composition may be
dispensed. The function of the breathing system is to convey
oxygen and anesthetic gases to the patient's lungs and remove
waste and anesthetic gases from the patient's lungs. Scavenging
equipment is not considered part of the breathing system.
The system is also referred to as breathing or patient circuit,
respiratory circuit or system.
Breathing system, semiclosed
is a system that allows some of the expired gases to leave
the circuit; the remainder mixes with the fresh gases and
is reinhaled. A CO2 absorber is used in this system.
are large-bore, nonrigid tubes composed of rubber or plastic
and used in most breathing systems to convey gases to and
from the patient's airway. They are usually corrugated to
prevent obstruction due to kinking and increase flexibility.
is defined as the area immediately adjacent to the employee’s
nose and mouth; a hemisphere forward of the worker’s
shoulders with a radius of approximately 6 to 9 inches.
is an instrument designed to facilitate the change of a liquid
anesthetic into its vapor and to add a controlled amount of
this vapor to the fresh gas flow.
Carbon dioxide (CO2)
is a colorless, odorless gas, and is a normal end product
of human metabolism. It is formed in the tissues and eliminated
by the lungs.
Carbon dioxide absorber
is a device used to remove CO2 chemically from exhaled patient
gas. Primarily used in the closed or semiclosed circle breathing
system, which requires carbon dioxide absorption to make reinhalation
of previously exhaled gas possible.
is the ability of a substance to cause cancer.
are also known as unidirectional valves, one-way valves, and
inspiratory and expiratory valves (refer to definition of
Common (fresh) gas outlet
is the port through which the mixture of gases and vapors
dispensed from the anesthesia machine is delivered to the
breathing system. Also referred to as the machine outlet.
is defined as any material or mixture having in the container
an absolute pressure exceeding 40 psig at 70°F or having
an absolute pressure exceeding 104 psig at 130°F.
are fittings intended to join together two or more components.
Cylinder supply source
is a cylindrical-shaped tank that is color-coded and pin-indexed
or Compressed Gas Association (CGA) valve-specific and used
to contain a specified medical gas. It supplies compressed
gas to the anesthesia machine if a pipeline supply source
is not available or if the pipeline fails. Cylinders range
in size from B (smallest) to H (largest).
Cylinder pressure gauge
monitors the pressure of gas within a cylinder.
Diameter Index Safety System
(DISS) provides threaded noninterchangeable
(gas-specific) connections for medical gas lines at pressures
of 200 psig or less to minimize the risk of misconnection.
is the study of health and illness in human populations. It
is the study of trends and events in similar populations,
for example, one exposed to a chemical and one not exposed.
are those gases and anesthetic vapors that are delivered to
the breathing circuit in excess of the patient’s requirements
and the breathing circuit’s capacity. These gases are
released from the breathing circuit via the APL or pop-off
valve or the ventilator pressure relief valve and are ultimately
removed from the breathing circuit by the waste gas scavenging
Exhalation check valve,
also known as expiratory unidirectional valve, refers to that
valve placed in the vicinity of the CO2 absorber that ensures
that exhaled gases flow away from the patient and into the
Flow control valve,
also known as the needle valve, controls the rate of flow
of a gas through its associated flow meter by manual adjustment
of a variable orifice.
a device that measures and indicates the flow rate of a gas
passing through it.
Gas is defined
as a formless fluid that expands readily to fill any containing
vessel, and which can be changed to the liquid or solid state
only by the combined effect of increased pressure and decreased
is a connection that does not allow bubbling when immersed
in water and subjected to a differential pressure.
is a state of unconsciousness in which there is an absence
of pain sensation.
is a device used to attach a reserve gas cylinder to the anesthesia
machine. The functions of the hanger yoke are to orient and
support the cylinder, provide a gas-tight seal, and ensure
a unidirectional flow of gas into the machine. It is pin-indexed
according to a gas-specific safety system in order to prevent
the connection of a cylinder of one gas to a yoke intended
also known as the heating, ventilating, and air conditioning
system, supplies outdoor replacement (make-up) air and environmental
control to a space or building. It conditions the air by supplying
the required degree of air cleanliness, temperature and/or
Inhalation check valve,
also called inspiratory unidirectional valve, refers to the
valve placed in the vicinity of the CO2 absorber that ensures
that the gases flow toward the patient.
is any gaseous substance that meets medical purity standards
and has application in a medical environment. Examples are
oxygen, nitrous oxide, helium, air, nitrogen, and carbon dioxide.
Medical gas mixture
is a mixture of two or more medical gases to be used for a
specific medical application.
(recommended exposure limits) are occupational exposure limits
recommended by NIOSH as being protective of worker health
and safety over a working lifetime. These limits are generally
expressed as 8- or 10-hour TWAs for a 40-hour workweek. The
REL may also be expressed as a short-term (TWA) exposure limit
or a ceiling limit.
Nitrous oxide (N2O)
is used as an anesthetic agent in medical, dental, and veterinary
operatories. It is a weak anesthetic with rapid onset and
rapid emergence. In hospitals, it may be used with oxygen
as a carrier gas for other, more potent anesthetics. In dental
offices, it is administered with oxygen, primarily as an analgesic
(an agent that diminishes or eliminates pain in the conscious
patient) and as a sedative to reduce anxiety.
system takes in fresh outside air and processes
it by filtering and adjusting the humidity and temperature.
The processed air is circulated through the various rooms
in a facility, and then all of it is exhausted to the atmosphere.
Whatever volume of fresh air is introduced into a room is
ultimately exhausted outdoors.
to waste anesthetic gases includes exposure to any inhalation
anesthetic agents that escape into locations associated with,
and adjacent to, anesthetic procedures. Such locations include,
but are not limited to, operating rooms, delivery rooms, recovery
rooms, and dental operatories.
is an element which, at atmospheric temperatures and pressures,
exists as a colorless, odorless, tasteless gas. Its outstanding
properties are its ability to sustain life and to support
combustion. Although oxygen is nonflammable, materials which
burn in air will burn much more vigorously and create higher
temperatures in oxygen or oxygen-enriched atmospheres.
Oxygen flush valve
is a separate valve designed to rapidly supply a large volume
of oxygen to the breathing system.
anesthesia care unit) is also known as the recovery room.
is the end of the component part nearest the patient.
is a device installed in the exhalation limb of the patient
circuit that allows positive end-expiratory pressure to be
delivered to the patient's airway and adjusted as needed.
is a sample collected from an individual’s breathing
Pin Index Safety System
is a safeguard to eliminate cylinder interchanging and the
possibility of accidentally placing the incorrect gas on a
yoke designed to accommodate another gas. Two pins on the
yoke are so arranged that they project into the cylinder valve.
Each gas or combination of gases has a specific pin arrangement.
Pipeline supply source
is a permanently installed piped distribution system that
delivers medical gases such as oxygen, nitrous oxide, and
air to the operating room.
pertaining to or operated by air or other gas under pressure.
is an accessory outlet located on an anesthesia machine that
supplies a driving gas for auxiliary equipment such as a ventilator.
Driving gas is normally oxygen, but medical air may be used.
Pressure relief valve
is a mechanical device that eliminates system overpressure
by allowing the controlled or emergency escape of liquid or
gas from a pressurized system. The relief valve may or may
not be adjustable.
for pounds per square inch gauge, which is the difference
between the measured pressure and surrounding atmospheric
pressure. Most gauges are constructed to read 0 at atmospheric
Recirculating ventilation system
returns part of the exhaust air to the air supply duct. The
system takes in an amount of fresh outside air that varies
as a function of the outside temperature. Air exhausted from
a room is filtered for particulate matter and bacteria, not
anesthetic gases, and then recirculated through several rooms
by means of a common mixing (plenum) chamber. In this process,
some fresh air is added and an equal amount of recirculating
air is exhausted.
is the patient care location where recovering patients are
awakened and stabilized and/or awakened after surgical anesthesia.
Anesthetic gases are exhaled by recovering patients (who received
inhalation anesthetics) as they breathe.
is also known as the respiratory bag or breathing bag. It
allows accumulation of gas during exhalation so that a reservoir
is available for the next inspiration. It provides a means
whereby anesthesia personnel may assist or control ventilation.
It can serve, through visual and tactile observation, as a
monitor of a patient’s spontaneous respirations and
acts to protect the patient from excessive pressure in the
is the process by which a rapid exchange of oxygen and carbon
dioxide takes place between the atmosphere and the blood coming
to the pulmonary capillaries. Oxygen is taken up, utilized
in metabolic processes, and a proportional amount of carbon
dioxide is released.
is defined as the collection of excess gases from the breathing
circuit and removal of these gases to an appropriate place
of discharge outside the working environment.
Scavenging system is
defined as a device (assembly of specific components) that
collects and removes the excess anesthetic gases that are
released from the breathing circuit. Scavenging systems are
also called evacuation systems, waste anesthetic gas disposal
systems, and excess anesthetic gas-scavenging systems.
is an engineering control designed to collect and remove excess
anesthetic gases at the point of origin (i.e., from the breathing
circuit or in close proximity to the patient’s mouth
and nose). It can be either a scavenging system or local (auxiliary)
exhaust ventilation system.
is a sample collected at the origin of contamination (source
also called the endotracheal tube, intratracheal tube, and
catheter is inserted into the trachea and is used to conduct
gases and vapors to and from the lungs.
TWA is a time-weighted
average concentration. It is a way of expressing exposure
such that the amount of time spent exposed to each different
concentration level is weighted by the amount of time the
worker was exposed to that level.
is a valve that allows gas flow in one direction only. Two
unidirectional valves are used in each circle system to ensure
that the gases flow toward the patient in one limb of the
circle breathing system and away in the other. They are usually
part of the absorber assembly.
Vapor is the
gaseous phase of a substance which at ordinary temperature
and pressure exists as a liquid.
(1) the physical process of moving gases into and out of the
lungs. (2) It is also defined for the purposes of industrial
hygiene engineering as a method for providing control of an
environment by strategic use of airflow. The flow of air may
be used to provide either heating or cooling of a work space,
to remove a contaminant near its source of release into the
environment, to dilute the concentration of a contaminant
to acceptable levels, or to replace air exhausted from a space.
Waste anesthetic gases
are those gases that are inadvertently released into the workplace
and/or can no longer be used. They include all fugitive anesthetic
gases and vapors that are released into anesthetizing and
recovery locations, from equipment used in administering anesthetics
under normal operating conditions, as well as those gases
that leak from the anesthetic gas scavenging system, or are
exhaled by the patient into the workplace environment. Waste
gases are also those excess gases in the breathing circuit
that are ultimately scavenged. Spills of liquid anesthetic
agents also contribute to ambient levels of waste gases. Waste
anesthetic gases may include N2O and vapors of potent inhaled
volatile anesthetic agents such as halothane, enflurane, isoflurane,
desflurane and sevoflurane.