2. INTRODUCTION
Health care facilities use pipeline systems to deliver nonflammable
gases such as oxygen, nitrous oxide, air, carbon dioxide, and
nitrogen to anesthetizing locations and other patient care areas.
Are installed by mechanical contractors and are maintained by the
engineering or maintenance department of the health care
facility, usually with little input from anesthesia providers
A survey by the determined that there is a significant knowledge
deficit among anesthesia practitioners related to the pipeline
systems
Anesthesia personnel should play a key role in designing the
piping systems.
The National Fire Protection Association (NFPA), the Compressed
Gas Association (CGA), the Canadian Standards Association
(CSA), and the International Standards Organization (ISO) have
set standards of construction
3. COMPONENTS
A medical gas distribution system includes a central
supply, piping extending to locations where the gas
may be required, and terminal units at each use point.
Hoses that extend from terminal units to the anesthesia
machine or other equipment, are not part of the piped
system
4. Supply Sources
May be located
Outdoors (with the control panel protected from the
weather) in an enclosure used only for this purposes
In a room or enclosure within a building
Access to the central supply area should be restricted to
individuals familiar with and responsible for the
system.
5. Two cylinder banks (units) are present
Each bank must contain at least an average day's supply
with a minimum of two cylinders
Larger amounts may be necessary in areas remote from
suppliers.
The cylinders are connected to a common manifold
(header) that converts them into one continuous
supply
A check (nonreturn) valve is placed between each
cylinder lead and the header to prevent loss of gas
from the manifolded cylinders if there is a leak in an
individual cylinder or lead.
6. The primary (duty, running) supply is the portion
supplying the system at any time, while the other bank
is the secondary (standby) supply
When the primary supply is unable to supply the system,
the secondary supply automatically becomes the
primary supply.
A reserve supply is often added
The reserve is used for emergencies or when
maintenance or repair is needed
7. The reserve system size depends on the rate at which gas
is used.
A precaution against gas supply disruption is to place the
reserve supply in a different area from the primary and
secondary supplies and for the reserve supply to enter
the facility by a different route
8. Further safety may be achieved by separating the
primary and secondary supplies so that the secondary
supply can be accessed if the primary supply fails
A pressure-reducing (operating) regulator is installed in
the main supply line upstream of the pressure relief
valve.
The pressures at which gases are piped vary, depending
on the country.
9. In the United States, gases other than nitrogen and
instrument air are normally piped at 345 to 380 kPa (50
to 55 psi).
Nitrogen and instrument air are usually delivered at 1100
kPa (160 psi).
The NFPA now permits pressures up to 2068 kPa (300
psi)
All final line regulators must be duplexed with suitable
valving to permit service without completely shutting
down the piped gas system
10.
11. OXYGEN
Oxygen may be stored either as a cryogenic liquid at low
pressures or as compressed gas in cylinders.
Gaseous Supply
Oxygen may be supplied from compressed gas
cylinders (usually G and H cylinders) that are
transported between the distributor and the central
supply area or from cylinders that are fixed at the site
and refilled by the distributor.
12. When large amounts of oxygen are required, it is less
expensive and more convenient to store it as a liquid.
Liquid oxygen containers are refilled from supply
trucks without interrupting service.
Alternatively, filled liquid containers may be
transported between the supplier and the facility.
Liquid oxygen containers are installed at ground level
so that they are readily accessible to supply trucks
The containers should be located where exposure to
potential ignition sources is minimal.
NFPA standards specify how far the container must be
from sidewalks, parked vehicles, and other objects.
13. To prevent the liquid from evaporating, it must be kept
at or below its boiling point (-297°F) by keeping it in
special insulated vessels.
These containers vary in size and shape.
Are constructed like Thermos bottles with outer and
inner metal jackets separated by insulation and a layer
that is near vacuum to retard heat transfer from the
exterior.
Each container should have a contents indicator and
low liquid level alarm. Gaseous oxygen is drawn off as
required and passed through a heater to bring it up to
ambient temperature and raise its pressure.
Although the tank is well insulated, a small amount of
heat will be continuously absorbed from the
surroundings, causing the liquefied gas to evaporate.
14. The amount of this uncontrolled evaporation is
normally less than the demand for the piped system.
If there is no flow from the container to the pipeline
system, the pressure in the container will slowly
increase until the safety relief valve opens and oxygen
is vented to atmosphere.
If a liquid system is left standing unused for a long
period of time, a significant amount of oxygen will be
lost.
Using liquid containers is economical only when there
is a fairly constant demand. Having the proper size
container will minimize oxygen loss from venting.
15. Most of the time, the oxygen is kept cold by the latent
heat of vaporization as gaseous oxygen is removed and
the temperature falls.
As the temperature falls, the pressure within the tank
also falls.
To maintain pressure, liquid oxygen must be removed
from hot water the tank and passed through a
vaporizer (evaporator, vaporizing column, gasifier),
which supplies heat.
This consists of a coil, tube, or mesh that is heated by
using electricity
A third possible oxygen source to feed the oxygen
pipeline is a supply system with oxygen concentrators
16.
17. Nitrous Oxide
Most facilities use manifolded cylinders to supply
nitrous oxide to the pipeline system.
One problem with nitrous oxide cylinders is that the
regulator may become so cold that it freezes.
Nitrous oxide may also be stored as a liquid at low
pressure in special insulated vessels similar to those
used for oxygen.
Warning signs should be posted around areas where
nitrous oxide tanks are located to caution that nitrous
oxide is an asphyxiant and that if there is a leak, a
hypoxic mixture may be produced
18. Piped Distribution System
There are three general classes of
piping:
Main lines—Pipes connecting the
source to risers or branch lines or
both.
Risers—Vertical pipes connecting
the main line with branch lines on
various levels of the facility.
Branch (lateral) lines—The
sections of the piping system that
service a room or group of rooms
on the same level of the facility.
19. Piped system layouts vary considerably.
Pipes are made of copper.
Generally, oxygen is installed in 1/2-inch outer
diameter (OD) and other gases in 3/8-inch OD pipes.
Pipes must be identified at least every 20 feet and at
least once in every room and story traversed by the
piping system to ensure that those installing and
maintaining the pipeline are aware of its content.
The name and pressure of the gas inside the pipe and
its flow direction must be displayed.
Flexible hoses are restricted to exposed areas where
they can be inspected and maintained. They cannot
penetrate or be concealed in walls, floors, ceilings, or
partitions
20. Pressure Relief Valves
Each central supply system must have a pressure relief
valve set at 50% above normal line pressure
downstream of the line regulator(s) and upstream of
any shutoff valve.
This relief valve prevents pressure buildup if a shutoff
valve is closed.
The valve should close automatically when the excess
pressure has been relieved.
21. Shutoff Valves
Permit specific areas of the piping system to be
isolated in the event of a problem as well as for
maintenance, repair, testing, or expansion without the
whole system being turned OFF. There are two types
of shutoff valves:
Manual :must be installed where they are visible and
accessible at all times.
Service shutoff valves :Are designed to be used only by
authorized personnel. They are in locked cases or have
their handles secured and tagged to prevent accidental
closing.
22. Manual valves are installed in boxes with frangible or
removable windows .
A quarter-turn valve with an indicating handle has become
standard .
Each valve should be marked to indicate its function, gas,
and area controlled as well as a caution that it should be
closed only in an emergency.
A shutoff valve is required at the outlet from the supply
source. This allows the entire supply source to be isolated.
23. The main supply line must be equipped with a manual
shutoff valve near the entry into the building unless the
source shutoff valve is accessible from within the building.
It should be at a location well known and readily accessible
to those responsible for maintaining the system but where
any attempt to tamper with it would be noticed.
Each riser must be equipped with a manual shutoff valve
adjacent to the connection to the main supply line.
Each branch (lateral) line except those lines supplying
anesthetizing locations and other vital life support and
critical areas (such as postanesthesia care, intensive care,
and coronary care units) must have a service shutoff valve
where the lateral branches off the riser.
A manual shutoff valve is required immediately outside
each vital life support or critical care area and must be
readily accessible in an emergency.
24.
25. Emergency Oxygen Supply Connector
When the central oxygen supply is located outside the building it
serves and there is not a connected oxygen reserve sufficient for an
average day's supply inside the building, a fitting for connecting a
temporary auxiliary supply source for emergency or maintenance
situations is required
Inlet must be located on the building's exterior and be protected
The pipe from this fitting attaches to the main supply line immediately
downstream of the main line shutoff valve
The inlet should be located where a supply vehicle will have year-round
access.
In-building emergency reserves may be used in place of the emergency
oxygen supply connector.
26. Alarms
Alarm Types
Master Alarm System
A master alarm system monitors the central supply and the distribution
system for all medical gas systems
.To ensure continuous responsible observation, master signal panels must
be located in two separate locations, wired in parallel to a single sensor
for each condition.
A centralized computer system may be substituted for one of the master
alarms
27. Area Alarm Systems
Critical life support areas such as operating room suites, postanesthesia
care units, intensive care units, coronary care units, and the like must
have an area (local) alarm system to indicate if the pressure increases or
decreases 20% from normal line pressure.
In anesthetizing locations, the alarm will be upstream of the shutoff
valves to the individual rooms.
An appropriately labeled warning signal panel for area alarms must be
installed at the nurses' station or other suitable location that will
provide responsible surveillance
28. Local Alarms
Local alarms are installed to monitor the function of the central medical
and instrument air systems as well as the vacuum and anesthetic gas
scavenging systems.
. The signals may be located on or in the control panel of the machinery being
monitored, within a monitoring device, or on a separate alarm panel
29.
30. Alarm Conditions and Responses
General Requirements
Each alarm must be labeled for the gas and area
monitored.
Signals should be both audible and visual. Some
systems allow the audible signal to be audio paused
(temporarily silenced).
The visual signal should continue until the problem is
corrected. Each panel should contain a mechanism to
test the alarms.
Alarms should be designed to function during
electrical power failure.
31. Clear, concise instructions should be given to the
persons monitoring the alarms to ensure that signals
are reported promptly to the proper parties
It is important to update alarms when source equipment
is updated or replaced
32. Alarm Conditions
An alarm should signal
(a) when the main supply reaches an average day's supply,
(b) when the reserve supply or in-building emergency reserve
begins to supply the system,
(c) when the reserve supply is reduced to one average day's
supply
(d) when the pressure in the reserve supply is below that
required to function properly
(e) when the secondary supply becomes the primary supply
(f) when the pressure in the main line increases or decreases
from normal operating pressure,
(g) when the dew point has been exceeded in the medical air
or instrument central supply system.
33. Pressure Gauges
A pressure gauge must be installed downstream of each
pressure regulator.
It is important that the gauge be on the downstream side of
a zone valve so that when the valve is closed, this will be
indicated by the pressure gauge
Pipeline pressure gauges are present on all anesthesia
machines. This allows the anesthesia provider to keep a
continual check on pipeline pressure in that location.
If a significant decrease or increase in pressure occurs, the
anesthesia provider should notify the proper personnel and
consider using gas from the cylinders on the machine.
34. Terminal Units
The terminal unit
station outlet
junctional point
interface
pipeline outlet
end use terminal
service outlet
terminal outlet
outlet point, outlet station
outlet assembly, wall outlet
The point in a piped gas distribution system at which the user
normally makes connections and disconnections. Equipment
may be connected to a terminal unit either directly or by a
flexible hose
35. Components
Base Block
The base block is the part of a terminal unit that is
attached to the pipeline distribution system.
Primary Valve
The primary valve (automatic shutoff valve; terminal unit
valve or check valve; terminal valve; self-sealing valve,
device, or unit; primary check valve)
Opens and allows the gas to flow when the male probe is
inserted and closes automatically when the connection is
broken.
Serves to prevent gas loss when the removable component
is disconnected.
Not a unidirectional valve and when open will permit flow
in either direction.
36. Secondary Valve
The secondary valve (shutoff valve, terminal stop valve,
maintenance valve, automatic service valve, isolating
valve, secondary valve, secondary shutoff valve,
secondary check valve)
Designed so that when the primary valve is removed
(e.g., for cleaning or servicing)the gas flow is shut off.
When the primary valve is in place, the secondary
valve stays open.
With hose booms and pendants incorporating hoses,
the secondary valve is fitted at or near the end of the
permanent pipework.
37. Gas-specific Connection Point (Socket Assembly)
The receptor for a noninterchangeable gas-specific connector that
is either part of or attached to the base block is incorporated into
each terminal unit.
The connector may be a threaded Diameter Index Safety System
(DISS) or a proprietary (manufacturer-specific) quick connector.
The corresponding male component of the noninterchangeable
connection is attached to the equipment to be used or to a
flexible hose leading to the equipment.
The female component is called an outlet connector or socket. The
male member is called an inlet connector, probe, plug, striker, or
jack.
Each DISS or quick connector must be equipped with a backflow
check valve to prevent gas flow from the anesthesia apparatus or
other dispensing apparatus into the piping system.
38. The Diameter Index Safety System
The DISS was developed to provide noninterchangeable
connections for medical gas lines at pressures of 1380 kPa (200
psi) or less (18). each DISS connector consists of a body, nipple,
and nut combination.
There are two concentric and specific bores in the body and two
concentric and specific shoulders on the nipple (Fig. 2.10).
The small bore (BB) mates with the small shoulder (MM), and the
large bore (CC) mates with the large shoulder (NN)
To achieve noninterchangeability between different connectors,
the two diameters on each part vary in opposite directions so
that as one diameter increases, the other decreases.
Only properly mated parts will fit together and allow the threads to
engage.
The American Society for Testing and Materials (ASTM) anesthesia
workstation requires that every anesthesia machine have a DISS
fitting for each pipeline inlet (Fig. 2.11) (19).
39. Quick Connectors
Quick connectors (automatic quick
couplers valves, quick connects,
quick-connect fittings, quick
couplers)
Allow apparatus (hoses, flowmeters, etc.)
to be connected or disconnected by a
single action by using one or both
hands without the use of tools or
undue force.
Quick connectors are more convenient
than DISS fittings but tend to leak
more.
Each quick connector consists of a pair of
gas-specific male and female
components
A releasable spring mechanism locks the
components together.
Hoses and other equipment are
prevented from being inserted into an
incorrect outlet by using different
shapes and/or different spacing of
mating portions.
40. Face Plate
The face plate should be
permanently marked with the
name and/or symbol of the
gas that it conveys. The
identifying color may also be
present.
41. Types
Wall Outlets
Wall outlets are mechanically simple and
well suited to small rooms where the
equipment to be connected will be near the
wall.
In larger rooms, the hoses to the equipment
frequently must be long and are often draped
across the floor.
This leads to personnel tripping over the
hoses, difficulty in moving equipment, wear
and tear on the hoses, and debris
accumulation.
For large rooms, more than one set of wall
outlets may be advisable.
Ceiling-mounted Hoses
Ceiling-mounted hoses with the terminal unit
at the end of the hose may be used.
42. Hoses
Hoses (droplines, hose assemblies, low-pressure
hose assemblies, low-pressure flexible connecting
assemblies, flexible hose assemblies, pipeline pressure
supply hoses, hose pipes)
Used to connect anesthesia machines and other
apparatus to terminal units .
Each end must have a permanently attached,
noninterchangeable connector. The connector that
attaches to a terminal unit is called the inlet (supply)
connector. The connector that attaches to equipment
such as an anesthesia machine is the outlet
(equipment) connector
43. A color-coded hose and the name and/or chemical symbol
of the contained gas on each connector are desirable.
Most hoses have an imbedded braid in the wall for added
strength.
Hoses should be kept away from any heat source, especially
operating room lights, because contact may cause the hose
to rupture
Whenever possible, hoses should be kept off the floor.
44. It sometimes is necessary to disconnect the pipeline hoses to
move the anesthesia machine. This should be performed quickly
and preferably without opening the cylinder valve on the
anesthesia machine because the cylinder may become depleted
if the valve is not closed after the hose is reconnected. If the hose
must be disconnected for more than a few seconds, a cylinder
should be opened and then closed as soon as the hose is
reconnected.
Using several extension hoses is undesirable. It is better to use
one long hose, as resistance caused by multiple connections may
interfere with gas flow. One long hose is less likely to leak,
because most leaks occur in the connectors or where the
connector fits into the hose.
Hoses should be kept in good repair and approach the anesthesia
machine with a gentle curve, avoiding acute angulations or
stretching. After years of use, hoses can weaken, swell, or crack .
Personnel should periodically check for these problems and have
the hoses repaired or replaced, if necessary.
45. Testing Medical Gas Distribution Systems
Anesthesia personnel have an obligation to ensure that
the system is properly designed and is functioning
correctly, so a member of the department should
witness the tests performed, especially those for cross
connections. A personal independent check using an
oxygen analyzer or other gas monitor is an excellent
idea.
46. After the pipelines have been installed but before the
installation of terminal units and other system
components (e.g., source equipment, sensors for
alarms, pressure gauges, or pressure relief valves), the
line must be blown clear of foreign material by using
oil-free dry nitrogen
47. Initial Pressure Test
Before system components are attached but after the
terminal units are installed and before closing of the
walls, each section of the piping system must be
subjected to a test pressure of 1.5 times the system
working pressure, but not less than 1035 kPa (150 psi),
by using oil-free nitrogen with the source valve closed.
This pressure is maintained until each joint has been
examined for leakage.
If any leaks are found, they must be corrected.
48. Test for Cross Connections
Testing for cross connections (anticonfusion or continuity test) is done to
ensure that the gas delivered at each terminal unit is that shown on the outlet
label and that the proper connectors are present at station outlets.
One gas system is tested at a time.
Each gas is turned off at the source valve and the pressures reduced to
atmospheric.
The pipeline being tested is then filled with oil-free nitrogen at its working
pressure.
With appropriate adapters matching outlet labels, each station outlet is
checked to ensure that test gas emerges only from the outlets of the medical
gas system being tested. The cross-connection test is then repeated for each gas
system in turn.
Pipeline Purge Test
To remove particulate matter, a heavy intermittent purging must be performed
on each outlet until no discoloration is produced on a white cloth that is held
over the outlet. The purging is started at the outlet closest to the zone shutoff
valve and is continued to the farthest outlet within the zone
49. Standing Pressure Test
Piping systems shall be subjected to a 10-minute standing pressure test
at operating line pressure.
Cross-connection Test
Either of the following tests can be used:
All medical gas systems are reduced to atmospheric pressure.
All sources of test gas from all medical gas systems, with the exception
of the one system to be checked, are disconnected. The system is then
pressurized to 345 kPa (50 psig).
Each terminal unit of every medical gas system is then checked to
verify that test gas is being dispensed only from the outlets of the
medical gas system being tested. Each medical gas system is checked in
this way.
The pressures of all medical gas system are reduced to atmospheric.
The test gas pressure in all the medical gas piping system is increased..
Following adjustment of pressures, each station outlet is identified by
label, and a gas-specific connector with a test gauge is attached to verify
that the pressure indicated is that listed.
50. Valve Test
Valves must be tested to verify proper operation and
rooms or areas that they control.
Alarm Test
All master and area alarm systems must be tested for
proper functioning.
51. Standing Pressure Test
After the walls have been closed and after installation of
station outlet valve bodies and other distribution system
components (e.g., pressure alarm devices, pressure
indicators, pressure relief valves, etc.), the entire system is
subjected to a 24-hour test with a pressure 20% above the
normal operating line pressure with the source valve
closed. Leaks must be located and repaired, and the test
must be repeated until no leaks are found.
System Verification
System verification tests shall be performed after all the
installer-performed tests have been completed. Testing
shall be conducted by a party who is technically competent
and experienced with pipeline installations and who meets
the requirements of ASSE 6000 (25).
52. Piping Particulate Test
A minimum of 1000 L of gas must be filtered through a clean, white
0.45 micron filter at a minimum flow rate of 100 L/minute. The filter
shall accrue no more than 1 mg of matter from any outlet tested.
Twenty-five percent of the zones must be tested at the outlet most
remote from the source.
Piping Purity Test
Each medical air system must be tested for dew point, methane, and
halogenated hydrocarbons at the outlet most remote from the source.
Maximum allowable values are given in NFPA 99 (2).
Final Tie-in Test
After connection of any work, extension, or addition to an existing
piping system, each joint in the final connection between the addition
and the existing system must be leak tested with the gas of system
designation at the normal operating pressure.
After the final connection is made and leak tested, the area
downstream of the point or area of intrusion must be purged.
53. Operational Pressure Test
Oxygen, nitrous oxide, and medical air outlets must
deliver 100 L/minute with a pressure drop of no more than
35 kPa (5 psi) at a static pressure of 345 to 380 kPa (50 to 55
psi). Nitrogen outlets and instrument air must deliver 140
L/minute with a pressure drop of no more than 35 kPa (5
psi) at a static pressure of 1100 to 1275 kPa (160 to 185 psi)
(2).
Gas Concentration Test
After purging each system with the gas for which the
system is designed, each system must be analyzed for gas
concentration. Allowable concentrations are given in NFPA
99 (2).
Medical Air Purity Test
The medical air source must be analyzed for dew point,
carbon monoxide, carbon dioxide, gaseous hydrocarbons,
and halogenated hydrocarboons.
54. Periodic Testing and Preventive Maintenance
A planned preventive maintenance program can
prevent potentially hazardous conditions and
unexpected loss of service, reduce the economic
burden from leaks, and reduce emergency repairs
Maintenance should be performed at least as
frequently as recommended by the pipeline
manufacturer and more frequently if required by
heavy use or local conditions.
Before maintenance is undertaken, the system should
be examined and the accuracy of existing diagrams
verified.
55. Inspection and testing should be performed on a
regular basis and the results recorded in a permanent
log.
If test buttons are provided at area panels , audible and
visual alarm indicators should be tested monthly.
All hoses and station outlets in the anesthetizing
locations and postanesthesia care units should be
checked at least monthly for wear, damage, and proper
function.
Terminal units should be checked for easy insertion,
locking, unlocking, and connector removal; leakage,
wear, and damage; contamination; gas specificity;
labeling; flow; and pressure.
56. Shutoff valves to anesthetizing locations can be checked for
tightness and components downstream of the valve for
leaks by the following test.
An anesthesia machine with a pipeline pressure gauge is
connected to the piping system.
Cylinder valves on the machines are closed, the zone
shutoff valve outside the operating room is closed, and gas
is released until each pipeline pressure gauge reads 280 kPa
(40 psig). This pressure is then monitored for 4 hours. It
should remain at 280 kPa.
If the pressure rises, the shutoff valve is not working
properly. If the pressure falls, there is a leak in the pipe to
the room, the station outlet, or the hose to the anesthesia
machine. It is essential that the shutoff valves be reopened
after this test has been performed.
57. It is good practice to check alarms regularly. Gauges in
area and master alarm panels should be monitored
daily for proper pressure.
The test button on alarm panels should be pressed
monthly to verify audible and visual signals. Burned
out bulbs should be replaced, and the testing should
be documented.
All master alarm signals should be tested at least
annually to verify proper operation. These signals are
required to be wired so that if a wire gets cut, it will
alarm. If removing the wire from the sensor does not
activate an alarm, it is not properly wired.
