Gas Cylinders and pipelines

Question 1

What are some laws associated with medical gases

Answer 1

Supply and sale regulated by the FDA
US DOT and OSHA regulate matters affecting safety and health of employees
Physical properties of medical gases should be considered as each gas has its own physical properties
Medical gases may be found throughout the hospital
The three most common gases (oxygen, nitrous oxide, air) are typically supplied via a central source
Alternatively “E” cylinders are available on the anesthesia machine

Question 2

physical principles of medical gases

Answer 2

Gases may be stored as liquefied gases (oxygen, nitrous, carbon dioxide) or compressed gases (oxygen, air)
The state in which a gas may be stored depends on its physical properties and the relationship between pressure, volume and temperature
Relationships are described by Gas Laws
Pressure is usually reported as kilopascals (kPa), centimeters of water (cmH2O), pounds per square inch (psi) or millimeters of mercury (mmHg)

Question 3

Critical pressure and critical temperature

Answer 3

Critical pressure and critical temperature are two important concepts that impact how medical gases are stored
Critical temperature of a gas is defined as the temperature above which a gas is unable to be liquefied, critical pressure is the pressure below which it becomes a gas
Critical temperature of oxygen is -118 C., and so oxygen exists as a gas at room temp
Critical temp of nitrous is 36.5 C and so at room temp nitrous exists as a liquid
To liquefy oxygen it must be cooled then pressurized

Question 4

Medical Gas Supply and Storage

Answer 4

Medical gases are stored in different types of cylinders ranging in size from 1.2 liters to 7900 liters which are fitted with different types of valves
Cylinders are mostly made of steel alloys or aluminum
Extreme temperatures and rapid temperature change must be avoided to prevent cylinder damage and leakage

Question 5

Cylinder Body

Answer 5

A, E, H sizes are most conventional
Traditional steel or aluminum
Some cylinders have integrated regulators
Minimum 0.26 inches thickness
Given pressure in a tank is the “service pressure”

Question 6

Compressed Gas Supply

Answer 6

H:Free-standing, attached to the machine by a flexible hose, regulated pressure 50 psi
E:Attached directly to the machine via a yoke (more mobile but more expensive)
Capacity:
E: Oxygen 660 liters, nitrous 1590 liters
H:Oxygen 6900 liters, nitrous 15800 liters

Question 7

Cylinder Valves

Answer 7

Common valve types include
Pin index valves
Bullnose valves
Hand-wheel valves
Integral valves
“E” cylinders typically have pin index valves
Large bulk cylinders for hospital pipelines are usually fitted with bullnose valves
“H” cylinders are usually fitted with hand-wheel valves

Question 8

gas-specific Connectors

Answer 8

Gas-specific pin-index system used on small cylinders
Gas-specific connectors used on large (G and H) cylinders
Difficult to attach a regulator or fitting to the wrong cylinder

Question 9

Medical Gas cylinder components

Answer 9

Body-Steel/alloy with flat base to stand on end, neck with tapered screw threads
Valve-Filling point located on neck of cylinder
Port-Point of exit for gas
Handle-Used to open or close valve, turned counterclockwise to open and release gas
Stem-Rotated during valve opening or closing. When valve is opened the stem moves upward, allowing gas to flow to the port

Question 10

Fusible Plug

Answer 10

Thermally operated, non-reclosing device
Offers protection from excessive pressure from high temperature but not from overfilling
Used on air and nitrogen cylinders
Replaced Wood’s metal

Question 11

Rupture Disc

Answer 11

Non-reclosing device with a disc held against an orifice
When the rated burst pressure is exceeded the disc ruptures
Gas flows from the approach channel into the atmosphere
Protects against excess pressure from high temperature or overfilling

Question 12

Pressure Relief Valve

Answer 12

Spring-loaded device designed to reclose and prevent cylinder contents from being discharged after normal pressure has been reached
When the set pressure is exceeded, the pressure in the cylinder forces the spring to the left and gas escapes into the atmosphere

Question 13

Gas Cylinder Facts

Answer 13

Some gases are in cylinder as gas (oxygen, air helium, nitrogen) and some are in liquid form (N2O, CO2)
Cylinder gas volume measured by amount of pressure in tank if in gaseous form, by weight if in liquid form
Cylinder must be inspected every five years
Safety systems help avoid incorrect gas connections and include color coding, pin indexing and diameter indexing
Oxygen should be changed at 1000 psi
Tag on cylinder should have three sections labeled “full”, “in use” and “empty”

Question 14

Pin-Indexed Safety Systems (PISS)

Answer 14

Safeguard introduced to eliminate cylinder interchanging (placing incorrect gas on yoke)
Two pins on the yoke are arranged so that they project into the cylinder valve
Each gas has a specific pin arrangement

Question 15

Regulatory Agencies and Industry Standards

Answer 15

Purity of medical gases is specified in the US Pharmacopeia and enforced by the Food and Drug Administration
Department of Transportation (DOT) have published requirements for the manufacturing, marking, labeling, filling, transportation, storage and disposition of medical gas cylinders
Safety and health of employees regulated by the Department of Labor and OSHA
National Fire Protection Association and Compressed Gas Association have published standards as well

Question 16

Cylinder Storage and Handling

Answer 16

Should not be handled with oily hands
Should not be stored near flammable materials
Should not be stored in extreme heat or cold
Paper or plastic covers should not be removed from the cylinders before storage

Question 17

Cylinder Hazards

Answer 17

Incorrect tank connection to yoke
Incorrect color, label or contents of tank
Inoperable or blocked valve outlets
Explosion
Damage to valve (dropped, etc.)
Empty tank

Question 18

Changing Cylinders

Answer 18

Avoid contamination with oil (fire hazard)
Make sure pins are present in yoke
Retract retaining screw, open gate
“Crack” cylinder to clear outlet of dust
Place cylinder on foot and raise to yoke
Engage pins and close gate
Tighten retaining screw
Open cylinder to make sure there is no leak
Most common cause of leak is missing or defective washer (use different tank and label)

Question 19

Medical Gas Pipeline Systems

Answer 19

Used to deliver nonflammable gases such as oxygen, nitrous oxide, air, carbon dioxide, and nitrogen
Standards established by National Fire Protection Association, Compressed Gas Association, and the International Standards Organization
Compliance with piping system standards is a basis for accreditation by JCAHO

Question 20

Supply Sources

Answer 20

Central supply system may be located outdoors, in a room or in a building enclosure
At least two cylinder banks are present, each one with at least two cylinders and a day’s supply of gas
The cylinders are connected to a common manifold that converts them into one continuous supply
A reserve supply is usually added

Question 21

Oxygen

Answer 21

May be stored as a cryogenic liquid at low pressures or as compressed gas in cylinders
Cylinders (G or H) are transported between the distributor and central supply area
Liquid oxygen containers are installed at ground level and refilled from supply trucks
Use of liquid containers is only practical when a significant, continuous amount is used
Oxygen concentrators may also be used

Question 22

Nitrous Oxide and Medical Air

Answer 22

Nitrous oxide is supplied with cylinders (H)
Medical air supplied by cylinders or motor-driven compressors (majority)
USP regulates quality standards
Air supply must be monitored for carbon monoxide and “dryness” (moisture must be removed)
Water is the most common contaminant of medical gas lines

Question 23

Diameter-Indexed Safety Systems (DISS)

Answer 23

Pipeline connections to the anesthesia machine use a diameter indexed safety system (DISS) to help prevent incorrect connections
The fitting for each gas has a different diameter, and each fitting is internally keyed so that the operator cannot make a loose connection with a slightly larger connection
“Quick Coupler” connections are now used to connect to gas station outlet, indexed so that only correct male-female components will attach

Question 24

Sources of Gas

Answer 24

Cylinder gas is reduced to 50 psig by regulator upon entering machine
Central oxygen depot is more economical for large hospitals, and a supply is available by pipeline with the pressure already reduced to 50 psig
To guard against failure, however, a cylinder supply must be readily available, and cylinder valve should be left open to supply gas if pipeline fails

Question 25

Hazards of Pipeline Systems

Answer 25

Leaks in the low pressure system are common
Fires and explosions may be caused by oxidizing ability of oxygen and nitrous oxide
Cross-connection of gas hoses is potentially lethal (prevented by gas-specific connectors)
Hypoxic gas mixtures may occur

Question 26

Alarm Systems

Answer 26

Master alarm monitors the central supply and distribution system
Area alarms in OR’s, PACU and ICU’s must have a local system to indicate if the pressure increases or decreases 20% from normal
Pressure gauges are downstream of each pressure regulator

Question 27

Medical Gas Alarm Panels

Answer 27

Area Medical Gas Alarm Panels are:
Provided so staff can be aware of the medical gas system servicing their work area
Designed to alarm when there are medical gas problems affecting your work area
Located throughout the hospitals/clinics, but there may not be a panel in your work area

Question 28

Problems with the Med Gas System

Answer 28

There are four ways to know about problems with the medical gas system:
Audible alarm on the panel
Visible alarm on the panel
Notification by Plant Services
Yellow or Orange Alert announcement for a medical gas servicefailure

Question 29

Patient Care is Priority

Answer 29

When there is a deficiency or alarm involving the medical gas system, continue to provide appropriate clinical care to patients
Assess the impact of the medical gas deficiency on patient care:
For high pressure alarms: identify all patients on that particular gas and reset any flow rates to the correct level
For low pressure alarms: assess the patients on that particular gas and provide an alternative cylinder supply for gas or portable vacuum pumps as necessary

Question 30

Alarms on ANY Med Gas Panel

Answer 30

Report any alarms associated with a Med Gas Panel immediately to the Charge Nurse, Plant Services, Respiratory Care, and the AC as outlined in VUMC policy SA 10-10.05, Area Medical Gas Alarm Panels
Refer to the Emergency Preparedness Quick Reference Guide for the appropriate system failure

Question 31

Gas Isolation Valves

Answer 31

The gas isolation valve is designed to isolate the medical gas supply for a particular area or room

Question 32

Gas Isolation Valves

Answer 32

May be used during certain emergencies, such as a fire involving the gas system or a major leak
Only the charge nurse is authorized to operate the shut-off valve after assessing and providing cylinder alternatives to affected patients

Question 33

Emergency Shut off

Answer 33

Remove the plastic cover from the valve box
Review the label in the valve box to ensure that the beds/areas served are consistent with the affected area
To operate the valve, turn the handle a quarter-turn until the valve handle stops