Gas Supply & Distribution Systems

Question 1

Gas Basics - pressure units

Answer 1

PSI

PSIg - doesn’t account for atm presure

PSIa- based on refernece point of 0 pressure for a perfect vacuum, = PSIg + atmospheric pressure

Question 2

Gas Basics - regulatory agencies

FDA

DOT

Answer 2

FDA - enforces medical gas purity

DOT - regulates how gas cylinders are manufactured, labeled, filled transported, stored, and disposed of

Question 3

Gas Basics - gases used

Answer 3

Oxygen

Air

Nitrous Oxide (N2O)

Helium

Nitrogen

Nitric Oxide (NO)

Carbon Dioxide

Question 4

Cylinder gases go through:

Answer 4

• A cylinder yoke
• An inlet filter
• A pressure gauge
• A check valve
• A high pressure regulator

A pressure relief valve vents to atmosphere if the regulated cylinder pressure is too high (approximately 65-75 psig).

Question 5

Pin Index Safety System (PISS)

Answer 5

• A safety feature to help ensure that cylinders are not installed on the wrong cylinder yoke
• Correct installation requires that the pins merge with the holes so that the cylinder can fit tightly into the yoke

Question 6

Function and pressures associated with primary regulators

Answer 6

Function: to lower the high gas pressure as it exits a cylinder & enters the system

Pressures associated: Maintain outgoing gas pressure at approximately 45-47 psi

Question 7

Function and pressure associated with pressure relief valve

Answer 7

Function: If the pressure in the gas supply module is too high, the pressure relief valve opens and vents the gas to atmosphere

Pressure: set to protect the machine if pressure exceeds 75psi

Question 8

E Cylinder Capacity & Pressures

Air, CO₂, He HeO₂, N₂, N₂O, O₂

Answer 8

L / psi

Air: 625/1900

CO2: 1590/838

He: 500/1600

HeO2: 500/+

N2: 610/1900

N2O: 1590/745

O2: 660/2200

Question 9

N2O cylinder use

Answer 9

M1V1 = M2V2

Volume of 1 mole at RT = 22.4 L/mol

Question 10

Oxygen cylinder use

Answer 10

P1/V1 = P2/V2

Question 11

Pipeline Supply Sources

Oxygen

Medical Air

Nitrous Oxide

Answer 11

Oxygen - Bulk liquid storage remote from hospital

Medical Air - Usually created by special hospital compressors with quarterly air quality monitoring (no tank)

N2O - Banks of G or H cylinders with automatic switching

Question 12

Diameter Index Safety System (DISS)

Answer 12

• Pipeline connections to the anesthesia machine used to help prevent incorrect connections.
• The fitting for each gas has a different diameter.
• Each fitting is also internally keyed so that the operator cannot make a loose connection with a slightly larger fitting

Question 13

Quick Connectors

Answer 13

• Quick connectors 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.

Question 14

Types of shut-off valves: manual vs service

Answer 14

• Isolate specific piping system areas without turning off entire system
• Manual Shut-off Valve: installed where they are visible & accessible at all times in boxes with frangile or removable windows
• Service shut-off valves: designed to be used only by authorized personnel, in locked cases or have their handles secured & tagged to prevent accidental closing

Question 15

Master vs Area Alarm Systems

Answer 15

• Master Alarm System - monitors the central supply & distribution system for all gases, signals changes in pressure, supply changeovers, & supply/reserve depletion
• Area (Local) Alarm System - monitors a specific area, signals pressure changes 20% above/below normal operating pressure

Question 16

Quarterly medical air testing purity requirements are done by what agency(ies)?

Answer 16

USP & NFPA