EXAM 1 - Lec 2 - Medical Gas Systems

What are 2 types of gas supplies?

-Gas cylinders
-Central pipeline

What are the most common type of cylinders we use?

E Cylinders

T/F Gas cylinders are compressed


T/F Gas containers are compressed


Gas cylinders can be compressed as either ___ or ____

Gas or liquid


Pounds per square inch


Pounds per square inch gauge

What is Psig definition?

difference between the measured pressure and the atmospheric pressure

Most gauges are constructed to read _____ at atmospheric pressure

0 mm Hg


Pounds per square inch absolute

Absolute pressure is based on a reference point of ____ pressure for a perfect _____

zero; vacuum

What is the definition of Psia?

psig + local atmospheric pressure

T/F Psia varies depending on where you are

True...at sea level atmospheric pressure is 0 but psia is 14.7

Compressed gas is any material or mixture of gases with an absolute pressure exceeding ____ psi at ____ degrees F

40 psi; 70�F

What is service pressure?

The maximum pressure that a cylinder may be filled at 70�F

A gas that remain gaseous at normal ambient temperatures and under pressures that range up to _____ psig

Non-liquefied compressed gas; up to 2500 pisg

What are examples of non-liquefied compressed gases?

Oxygen, Nitrogen, Air, Helium

T/F Non-liquefied compressed gases can be liquids at high temperature, the point where they are referred to as cryogenic liquids.

False...at LOW temperatures

A gas that becomes a liquid to a large extent at normal ambient temperatures and under pressures from _____- ____ psig

Liquified compressed gas; from 25-2500 psig

Examples of liquefied compressed gases

Nitrous Oxide and Carbon Dioxide

Tank containing a high pressure gas/gas mixture in a pressure that may be in excess of 2000 psig

Medical gas cylinder

Low pressure, vacuum-insulated vessel containing gases in a liquid form

Medical gas container (ex. liquid oxygen are stored in these containers to keep it cold)

What is the difference between a medical gas cylinder and container?

Cylinder has pressure

Who sets and determines purity specification of medical gas?

Pharmacopoeia of the United States

Who regulates and enforces the purity of medical gases?

Food and Drug Administration (FDA)

Who has published requirements for the design, construction, testing, manufacturing, marking, labeling, filling, qualification, transportation, storage, handling, maintenance, requalification, and disposition of compressed medical gas cylinders AND contai

Department of Transportation (DOT)

The DOT is in charge of everything except (2)

Purity and regulation

What is in charge of the installation of the piping system in clinical facilities?

National Fire Protection Association (NFPA)

Most medical gas cylinders are constructed of _____

(A lot of cylinders used on our anesthesia machine are made from aluminum to reduce weight)

How are aluminum cylinders marked?

3AL or 3ALM

Why is aluminum more useful?

Lighter and can be used in an MRI environment

What allows cylinders to stand on end?

Flat bottoms

Through which part of the cylinder is its content filled and/or discharged?


What is the actual point of exit of gas from the cylinder?

Port (located above the PISS holes)

It is important not to mistake the port for the _____

Conical depression (located above the pressure relief device)

What part rotates during valve opening or closing?

Stem (shaft)

To close the valve, the stem seals against the ____ that is part of the valve body


To OPEN the valve, the stem moves ____ to allow gas to exit the port


Most cylinders have which type of valve?

Packed valve
(the stem is sealed by resilient packing such as Teflon, which prevents leaks around the threads of the valve)

Packed valves are also called ___

Direct acting valves
(turning the stem causes the seat to turn)

T/F Packed valves can withstand high pressures


Turning a valve which way opens it?

Counterclockwise (righty tighty, lefty loosey)

How many turns are needed to fully open a packed valve?

2-3 full turns

T/F In a diaphragm valve the stem is separate from the seat


How many turns are needed to fully open a diaphragm valve?

1/2 or 3/4 of turn

Is packed valve or diaphragm valve less likely to leak?

Diaphragm valve

Which type of valve is present in E cylinder? In larger cylinders such as H or M cylinders?

-Packed valve in E cylinder
-Diaphragm valve in larger cylinder

What is used to open or close a cylinder valve?

Handle or handwheel

What is the major difference between a pressure relief device and a pressure relief valve?

- Pressure relief device: One-time use ONLY (once it is activated to allow discharge of cylinder content in the face of excessive pressure, the cylinder is NO LONGER usable)
-Pressure relief valve: Allows cylinder contents to be discharged when pressure b

T/F Once a pressure relief device is ruptured, it must be taken off and replaced


What is the purpose of a pressure relief DEVICE?

Allow gas to be released into the atmosphere when the pressure gets too high

Non-reclosing device with a disc help against an orifice
When the pressure becomes too high, the disc ruptures and allows the cylinder contents to be discharged

Rupture disc (Frangible disc)

Rupture discs protect against excess _____ as a results of high ____ or _____

pressure; temperature; overfilling

Thermally operated
Non-reclosing pressure relief device that uses a low melting point material with the plug held against the discharge channel

Fusible Plug

What is the common fusible plug used?

Wood's Metal

A fusible plug protects from excessive pressure caused by high ____ but NOT _____

Temperature ONLY!
NOT overfilling

Temperature at which the fusible material becomes sufficiently soft to extrude from its holder so that the cylinder contents can be discharged

Yield temperature

Prevent bursting at a predetermined pressure unless the temperature is high enough to cause yielding of the fusible material/metal

Combination rupture disc/fusible plug

Because a combination rupture disc/fusible plug function only in the presence of both excessive heat and excessive pressure, they do not offer protection from _____.


A spring-loaded mechanism designed to reclose and prevent cylinder contents from being discharged after a normal pressure has been restored.

Pressure relief VALVE

T/F Rupture discs or fusible plugs are more susceptible to leaks than pressure relief valve

False...pressure relief valve more susceptible to leaks than rupture discs or fusible plugs

Receives the retaining screw of the yoke

Conical depression

Why must the conical depression be distinguished from the pressure relief device below it?

If the retaining screw is tightened into the pressure relief device instead of the conical depression, the device may be damaged and the cylinder contents escape

What are three cylinder safety systems that reduce potential hazards of using the wrong gas?

1. Color coding
2. Pin Index Safety Systems
3. Valve outlet connections (larger cylinders)

What is the Pin Index Safety System?

-Present in cylinders sizes A through E (small to medium size cylinders)
-These are
on the cylinder valve positioned in an arc below the port
-Pins on the yoke or pressure regulator are positioned to fit into these holes
-Unless the pins and holes a

What are valve outlet connections?

-Usually for size M, H and larger
-Threaded outlet connections mesh with those of the nut. The nut may be tightened, causing the nipple to seat against the valve outlet. In this way, the gas channel of the valve is aligned with the channel of the nipple.

What are some ways valve outlet connections indexed? (5)

1. Diameter
2. Thread Size
3. Left or right handed threads
4. external vs. internal threading
5. Change in nipple/seat design

If the cylinder contains a gas mixture, it must have the color of each of the gas painted at the ___.

Top of the cylinder

Oxygen color


Nitrous Oxide color


Air color


Heliox color

Green and brown

Carbon dioxide color


Cylinder sizes are classified using a _____ code


E Cylinder Medical Air capacity in liters and psig

-1,900 psig

E Cylinder Nitrous Oxide capacity in pounds, liters, and psig

-6.4 pounds
-745 psig

E Cylinder Oxygen capacity in pounds, liters, and psig

-1.9 pounds
-1,900 psig

How do you calculate gas in an E cylinder?

Multiply the gauge pressure by 0.3 and then divide by the flow rate to get the minutes left in the tank
Ex: psig = 300; flow rate = 2L/min
300 x 0.3 = 90L /2L = 45 minutes remaining

T/F In a non-liquefied gas cylinder, the pressure in the cylinder will steadily decline as the contents are withdrawn

True...so pressure can be used to measure the cylinder contents

T/F In a liquefied gas cylinder (nitrous oxide) the pressure depends on the vapor pressure of the liquid, so the pressure remains constant until all the liquid has evaporated


The nitrous oxide cylinder will read _____ until it is almost empty

745 psi

What is the most reliable way to determine how much nitrous oxide is remaining in its cylinder?

Weigh the cylinder

When should testing and inspecting of cylinders occur?

5 years unless there is a special permit stamped on the cylinder in which case it can be 10 years

Who regulates cylinder filling?


What is the service pressure?

The max pressure to which the cylinder may be filled at 70�F

T/F A cylinder containing a gas under a safe pressure with normal temperature can become unsafe if the temperature rises (who's law is this....)

-Gay Lussac's Gas Law

The pressure in the filled cylinder at 70�F MAY NOT exceed the service pressure marked on the cylinder EXCEPT for ____

Nonliquefied, nonflammable gases such as
, He, CO2-O2 mixture, He-O2 mixtures which may be allowed an additional 10%

T/F Oxygen supports combustion but is not flammable by itself


Why should cylinder valves, pressure regulators, gauges, or fittings NEVER come in contact with oils, greases, organic lubricants, rubber, or other combustible substances?

Oils + O2/N2O under pressure can explode
-Cylinders or valves should NOT be handled with hands, rags, or gloves contaminated with oil or grease.
-Polishing or cleaning agents should NOT be applied to the valve as they may contain combustible chemicals.

What are the other safety rules for cylinders? (10)

1. Avoid extremes of temperature (>130 degrees F and < 20 degrees F)
2. Keep connections tight
3. Discharge port or valve outlet not be obstructed
4. Avoid mixing parts of cylinder used for one gas with cylinders containing other gases
5. NO adapters to c

What must be present for large cylinders when not in use?

Valve protection caps

T/F Lay the cylinder down on the floor. NEVER keep it standing on the floor with its flat bottom.


T/F You can store cylinders in the OR


Medical gas cylinders are best identified by ____

Reading the label! (NOT the color)

What is "cracking" the valve?

Before any fitting is applied i.e. placing the cylinder onto the anesthesia machine, particles of dust, metal shavings, and other foreign materials should be cleared from the outlet by removing the protective cap or seal then SLOWLY and BRIEFLY opening th

Why "cracking" the valve?

- Cracking the valve reduces risk of a FLASH FIRE or EXPLOSION when the valve is later opened with the fittings in place
-Also, the dust will be blown into the anesthesia machine where it could clog filters

What should you always use on a small cylinder? -When do you change this?

ONE sealing washer (gasket)
-Replace if hear hissing sound (leak)

T/F connections should mate properly


Why should the valve be opened slowly?

-If gas passes quickly into the space between the valve and the yoke or regulator, the rapid recompression in this space will generate large amounts of heat.
-Because there is little time for this heat to dissipate, this constitute an adiabatic process.

What do you do when hear a hissing sound when the valve is opened?

Tighten the connection and if hissing persists then replace the washer



T/F An empty or near empty cylinder should be removed from the anesthesia machine


How do you remove a cylinder from the anesthesia machine?

Before removing a cylinder from a regulator or yoke, close the valve and release all the downstream pressure by opening the flow control valve on the anesthesia machine and let it "bleed out

What is transfilling?

Transferring medical gas from one cylinder to another

T/F We are able to perform transfilling


Medical grade oxygen is ____% pure


Medical grade oxygen cannot contain more than ____ ppm carbon dioxide, ____ ppm carbon monoxide or ____ ppm nitrogen

300; 10; 5

What is the biggest danger in transfilling?

Causing temperature to rise so that you create combustion or oxidation of the metals in the valve

What are the advantages of Liquid Oxygen (LOX)? (5)

1. Low pressure gas
2. Very compact
3. Low weight
4. Portable
5. Simple to use

Liquid oxygen container must have a pressure relief _____ and ___

Valve! And a means to control how much oxygen is contained within it

When not in use, pressure in the liquid oxygen container is controlled by _____

Venting excess gas to the atmosphere which limits the time that oxygen can be stored in the portable unit b/c eventually pressure will be lost over time

What are the rules for safe use of LOX containers? (10)

1. If spilled, allow time to dissipate
2. Avoid skin contact - LOX will burn you
3. Avoid organic or combustible materials
4. Cryogenic transfilling devices must be free of moisture so that you don't get frost on the valve
5. Avoid temperature extremes -

Where can central pipeline systems be held?

Outdoors with closures to restrict public access

What is the max storage allowed for oxygen in a facility?

20,000 cubic feet

What are the two types of bulk supply?

1. Large storage tank outside
2. Bank of large cylinders in the hospitals itself

What is the boiling point for liquid oxygen

-297 degrees F (why we need to avoid skin contact)

How does liquid oxygen stay cold?

Latent heat of vaporization

Pressure-reducing regulator installed in the main supply line is upstream or downstream of pressure relief valve?


Medical gases are piped in at ____ psig EXCEPT for Nitrogen which is piped in at ____ psig

All medical gases (except nitrogen) = 50-55 psig
Nitrogen = 160 psig

T/F Medical air similar to N2O has no detectible liquid hydrocarbons and is more pure than ambient air in the environment


What is the Diameter Index Safety System?

-Non-interchangable connections so you can't connect the wrong hose to the wrong pipeline
-Each connector has a body, nipple, and nut
-Body has 2 concentric bores to match specific nipples
-Diameter of the bore is different for each gas
-Color coded accor

Steel cylinders are marked: