Medical Gas Systems and Cylinders

Medical Gas System and Oxygen Administration

• Respiratory care practitioners should know how to safely use medical gas supply systems in an institution
• Medical gas cylinders, piping, liquid systems, and oxygen concentrators are examples of supply systems
• Medical gas systems are safe and effective if used appropriately, but potentially lethal if mishandled

Medical Gas Cylinders: U.S. DOT Regulations

• Cylinders for medical gases must be constructed according to U.S. Department of Transportation (DOT) regulations
• The DOT specifies the materials and methods for constructing medical gas cylinders

Medical Gas Cylinders: Construction

• Medical gas cylinders are generally constructed from seamless steel meeting chemical and physical requirements
• Cylinders are formed by spinning or stamping a flat sheet into the proper shape, and then heat treated to retain the steel's tensile strength

Cylinder Markings: DOT Regulations

• Medical gas cylinders must have specific markings permanently stamped on the shoulder, per DOT regulations

Cylinder Markings: DOT 3AA

• The first marking on a medical gas cylinder is "DOT 3AA" which indicates the cylinder meets DOT standards for 3AA-type compressed gas cylinders
• The standards require to be of seamless construction and made from high-strength, heat-treated alloy steels with specific chemical compositions which withstand high stress
• This type of cylinder has a wall thickness less than that of other cylinder types and weighs less than cylinders of comparable size and service pressure

Cylinder Markings: Service Pressure

• The next stamp after the cylinder type shows service pressure, in pounds per square inch (psi), under which the cylinder was designed to operate
• The common service pressure for oxygen cylinders in medical use is 2015 psi

Cylinder Markings: Serial Number

• The number stamped immediately below the specification number is the serial number for that cylinder
• This number is unique and assigned by the manufacturer

Cylinder Markings: Manufacturer and Ownership

• The manufacturer's mark appears below the serial number and may be represented by initials or an abbreviation
• The ownership mark appears on the next line, and like the manufacturer's mark, it may be represented by initials

Cylinder Markings: Hydrostatic Testing

• If hydrostatic testing has been performed, the date of the test and the inspector's mark will be stamped on the cylinder shoulder
• The inspector's mark may appear between the month and day of the test, or after the month and day
• A plus sign (+) after the testing date indicates the cylinder may be charged up to 10% greater than the service pressure

Cylinder Markings: Hydrostatic Testing Details

• Hydrostatic testing is required every 5 or 10 years for cylinders in service
• The test involves placing the cylinder in a water-filled vessel and filling it to 5/3 the service pressure for 3A and 3AA cylinders
• The cylinder's expansion is measured under pressure and the test date and expansion data is recorded if within acceptable limits
• The cylinder is then stamped with the test date and inspector's mark
• Cylinders failing a hydrostatic test are destroyed

Common Medical Gas Cylinder Sizes

• The two most common medical gas cylinder sizes in clinical settings are "E" and "H/K"

Size E Cylinder Tanks

• Size E cylinder tanks are used for brief intervals due to their small capacity
• Their most common use is transporting patients or short-term therapy where piped gases aren't available
• The tanks' small size makes them ideal for transport situations
• Small mobile cylinder carts make transporting a patient in a wheelchair or gurney easier

Size H/K Cylinder Tanks

• The H/K cylinder is much larger than the E cylinder, containing a little more than 10 times as much gas
• Due to their size and construction, they are heavy, weighing about 135 pounds
• Special cylinder carts facilitate the transport of H/K cylinders

Color Coding: CGA

• The Compressed Gas Association (CGA) has developed a color code for different gases and gas mixtures, each with its own unique color
• This code is published by the U.S. Department of Commerce, under recommendation from the Bureau of Standards

Color Coding: United States vs International

• The U.S. color code system and the International color code system differ between the International systems is the color code for oxygen
• Oxygen is green in the United States, while white in international settings
• Carbon dioxide is gray in both settings
• Nitrous oxide is light blue in both settings
• Cyclopropane is orange in both settings
• Helium is brown in both settings

Color Coding: Labels

• All medical gas cylinders must have a label identifying contents, besides the color code
• The label's color code and the cylinder's color code should match
• Do not administer gas from a cylinder if there's doubt about the contents, such as a missing label or mismatching label and color code
• The cylinder should be tagged as mislabeled and returned to the medical gas supplier
• With the color code of the cylinder is verified and the label to the color code can the practioner be certain of the contents

Cylinder Valves

• Cylinder valves are needed to contain high-pressure gas and provide an equipment attachment point
• Cylinder valves are atop the cylinder, and there are two types: direct-acting and diaphragm

Cylinder Valves: Direct-Acting

• The direct-acting cylinder valve is a needle valve
• Washers and polytetrafluoroethylene (Teflon) gasket material prevent leakage of high-pressure gas through the threaded portion of the needle valve
• The plunger is raised from its seat, and gas flows as the valve stem is rotated counterclockwise
• This valve withstands high pressure, commonly found on cylinders holding gas at 1500 psi or greater

Cylinder Valves: Diaphragm

• The diaphragm cylinder valve contains a diaphragm that rests on the seat
• The pressure from the cylinder displaces the diaphragm, and gas flows as the valve stem is turned counterclockwise
• The valve plunger doesn't act directly on the valve seat in this type of valve
• This valve is generally found on cylinders containing less than 1500 psi of pressure

Cylinder Valve Safety Systems

• There are two safety systems incorporated into cylinder valves, one from the Bureau of Explosives and the other from the CGA
• A safety pressure relief is provided on the cylinder valve in case of excessive pressure buildup within the cylinder

Cylinder Valve Safety Systems: Frangible Disk or Fusible Plug

• One system consists of a frangible disk or a fusible plug
• With excessive pressure, the frangible disk fragments into small pieces, releasing pressure
• The fusible plug is made from a metal with a low melting point, and releases pressure when the temperature rises beyond the metal's melting point

Cylinder Valve Safety Systems: CGA Design

• Medical gas cylinders may contain a variety of gases, which is why a safety system was designed by the CGA to prevent interchange of cylinders containing dissimilar gases
• The American Standard Index system or the American Standard Safety System (ASSS) adopted the design

Cylinder Valve Safety Systems: Two Systems to Note

• Two safety systems prevent the interchange of cylinders containing different gases: one for large cylinders and one for E cylinders and small cylinders
• The large cylinder safety system utilizes different thread sizes and pitches, along with internal and external threading
• Due to threading variations, a cylinder containing one gas can't be connected to equipment indexed for a different gas

Cylinder Valve Safety Systems: Protective Caps

• Large medical gas cylinders have a protective cap that covers the cylinder valve
• The cap is threaded and matches threads on the cylinder shoulder just below the valve
• The protective cylinder valve cap must be in place when transporting the cylinder, following safe practice

Cylinder Valve Safety Systems: Small Cylinders D and E

• Small cylinder (D and E) valves use a yoke connection rather than a threaded connection for equipment attachment
• The face of the cylinder valve has two holes drilled in two of six specific positions
• The yoke attaches to the cylinder valve with pins indexed in corresponding positions
• If pin and hole positions don't match, the cylinder and yoke cannot be mated, preventing interchange of equipment or cylinders containing dissimilar gases, also is known as pin index safety system (PISS)

Safety Precautions: Medical Gas Cylinders

• Common sense and care are crucial when handling compressed gas cylinders
• Medical gas cylinders are safe when handled properly and with care
• Damage to personnel, buildings, and vehicles can result from improper cylinder handling, as documented

Safety Precautions: Oxygen Properties

• Most oxygen that practitioners administer will be from a medical gas cylinder
• Knowledge of oxygen's physical characteristics will help in handling medical gas cylinders
• Oxygen is colorless, odorless, and tasteless
• It supports life and is a requirement for combustion of any material
• It should not be considered flammable, though combustion will occur at a greatly accelerated rate if anything is burning in close proximity
• Petroleum products should not be used on any cylinder valve fittings or reducing valve fittings

Safety Precautions: Spontaneous Combustion

• Certain substances may ignite with great force when exposed to oxygen, even without added heat to initiate the process; this is called spontaneous combustion
• Such substances include oil, grease, and petroleum-based products like Vaseline in hospitals or transport situations
• The cylinder valves and fittings must be prevent from making contact with such products

Recommended Safe Practices: CGA Handbook

• The CGA has published recommended safe practices for handling medical gases in its 1999 Handbook of Compressed Gases, Fourth Edition

Moving Cylinders Safety: Best Practices

• Always leave protective valve caps in place when moving a cylinder
• Don't lift cylinders by their caps
• Don't drop them or strike two together or against other things
• Don't drag or slide them; use a cart
• Use a cart when loading or unloading cylinders

Storing Cylinders Safety: Best Practices

• Comply with local and state regulations and standards, for example, the NFPA
• Post the names of the gasses stored
• Keep full and empty cylinders separate, putting full cylinders in an easy-to-access area
• Store them in dry, cool, well-ventilated, fire-resistant areas
• Do not store cylinders near flammables like gasoline, grease, or petroleum
• Protect cylinders from abrasion, and do not store where there is potential damage from moving or falling things, and ensure the valve caps are on at all times
• Cylinders can be stored outside, but keep them off the ground by using a platform
• Protect cylinders from unauthorized access

Handling Cylinders Safety: Who Can Handle

• Only allow experienced, trained people to handle cylinders
• The user is to verify cylinder contents before use
• Do not use if there is doubt over contents; return instead
• Leave the protective valve cap on until ready to attach the regulator or other equipment

Withdrawing Cylinder Contents Safety: What To Do

• Cylinders are to be supported and protected from falling
• The right reducing valves or regulators should be used when attaching equipment designed for lower operating pressures than contained in cylinders

Withdrawing Cylinder Contents Safety: Connections and Fittings

• Do not force any threaded connections
• All threads should be verified to ensure they are designed for the gas or gas mixture
• Cylinders should only be connected to a manifold designed for high-pressure cylinders
• Equipment should only be used with the cylinders that contain the equipment's intended gases

Withdrawing Cylinder Contents Safety: Opening Valves

• Open all cylinder valves slowly
• Always use care when manipulating valves
• Treat cylinders and cylinder valves with care
• Compressed gases should not be used when dusting off clothing

Handling Cylinders Safety: Final Steps

• All connections should be kept tight to prevent leakages
• Before removing regulators, shut off the valve and relieve any pressure
• Never test for leaks with flammable gasses with a flame
• Ensure that flammable anesthetic gasses are kept away from oxygen, and stored separately

Gas Cylinder Capacities and Pressures

• The full cylinder pressure is 2,200 psi
• Cylinder capacities are as follows:
  • D = 12.7 cu. Ft. (356 L)
  • E = 22.0 cu. Ft. (622 L)
  • G = 187 cu. Ft. (5,260 L)
  • H/K = 244 cu. Ft. (6,905 L)
• 1 cubic foot = 28.3 liters

Calculation of Duration of Flow (DOF): Formula

• Duration of flow is a critical measure for transport and home care
• The time when the gas will run out in hours or munites
• • Formula: DOF (Time) = Gauge pressure x DOF factor / Flow (L/min)

DOF Factors

• The following are the factors of the correlating vessels:
  • D = 0.16 L/psi
  • E = 0.28 L/psi
  • G = 2.41 L/psi
  • H/K = 3.14 L/psi

DOF Computation: Formula

• • Formula: DOF Factor = Cu. Ft of gas in cylinder x factor to convert cu. Ft to liters / Full cylinder pressure

Calculating Cylinder Usage: Key Details

• The common sizes for O2 storage are the H cylinder and the E cylinder
  • The H cylinder can hold 244 cu ft (6900 L) of O2
  • The E cylinder used for transportation purposes, holds 22 cu ft (622 L) of O2
• 1 cu ft = there are 28.3 Liters

Calculating Cylinder Duration: The Formula

• Cylinder Duration (DOF) can be calculated with this formula:
  • Minutes remaining in cylinder = Cylinder pressure x Cylinder factor / Flow rate

Calculating Cylinder Duration: Example Scenario

• An example calculation for measuring flow time:
  • How long does it take for a full H cylinder running at 8 L/min to fully deplete?
    • 2200 psig x 3.14 L/psig / 8 L/min = 14.39 hours
    • 14.39 hours = (863.5 minutes, or 14 hours and 39 minutes).

More Calculating Cylinder Duration: Example Scenario

• If an E cylinder contains 1800 psig. How long will it take for the respiratory therapist to run the cylinder at 4 l/min to a level of 200 psig when attached to a nasal cannula