MEDICAL GAS PIPELINE SYSTEM

MEDICAL GAS PIPELINE SYSTEM-1 BY-DR Suchit khanduja INTRODUCTIONHealth 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 providersA 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

COMPONENTSA 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

Supply Sources

May be locatedOutdoors (with the control panel protected from the weather) in an enclosure used only for this purposesIn a room or enclosure within a buildingAccess to the central supply area should be restricted to individuals familiar with and responsible for the system.

Two cylinder banks (units) are presentEach bank must contain at least an average day's supply with a minimum of two cylindersLarger amounts may be necessary in areas remote from suppliers. The cylinders are connected to a common manifold (header) that converts them into one continuous supplyA 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.

The primary (duty, running) supply is the portion supplying the system at any time, while the other bank is the secondary (standby) supplyWhen the primary supply is unable to supply the system, the secondary supply automatically becomes the primary supply. A reserve supply is often addedThe reserve is used for emergencies or when maintenance or repair is neededThe 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

Further safety may be achieved by separating the primary and secondary supplies so that the secondary supply can be accessed if the primary supply failsA 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.

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

OXYGENOxygen 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.

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.

To prevent the liquid from evaporating, it must be kept at or below its boiling point (-297F) 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. 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.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 electricityA third possible oxygen source to feed the oxygen pipeline is a supply system with oxygen concentrators

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 producedPiped Distribution SystemThere are three general classes of piping:Main linesPipes connecting the source to risers or branch lines or both.RisersVertical pipes connecting the main line with branch lines on various levels of the facility.Branch (lateral) linesThe sections of the piping system that service a room or group of rooms on the same level of the facility.

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 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.

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.

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.

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.

Emergency Oxygen Supply ConnectorWhen 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 requiredInlet 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. AlarmsAlarm TypesMaster Alarm SystemA 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 alarmsArea 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

Local AlarmsLocal 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

Alarm Conditions and ResponsesGeneral RequirementsEach 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.

Clear, concise instructions should be given to the persons monitoring the alarms to ensure that signals are reported promptly to the proper partiesIt is important to update alarms when source equipment is updated or replaced

Alarm ConditionsAn 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. 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.

Terminal UnitsThe terminal unit station outletjunctional point interface pipeline outletend 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

Components Base BlockThe base block is the part of a terminal unit that is attached to the pipeline distribution system. Primary ValveThe 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.

Secondary ValveThe 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.

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.

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).

Quick ConnectorsQuick 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.

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.

TypesWall 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 HosesCeiling-mounted hoses with the terminal unit at the end of the hose may be used.

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) connectorA 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.

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.

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.

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 Initial Pressure TestBefore 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.Test for Cross ConnectionsTesting 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 TestTo 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

Standing Pressure TestPiping 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.

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.

Standing Pressure TestAfter 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 VerificationSystem 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).

Piping Particulate TestA 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 TestEach 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 TestAfter 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.

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.Periodic Testing and Preventive MaintenanceA 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.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.

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.

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.

THANX!!