Medical Gases Flashcards
1atm = ? psi
1atm = 14.7psi
PSI
pounds per square inch
psig
pounds per square inch gauge
o Difference btw measured pressures and surrounding atmospheric pressure with most gauges constructed to read zero at atmospheric pressure
psia
pounds per square inch absolute
o Absolute pressure based on reference point of zero pressure for perfect vacuum
o = psig + local atmospheric pressure
Nonliquefied compressed gas
gas that does not liquefy at ordinary ambient temperature regardless of pressure applied
o Oxygen, nitrogen, air, helium
Cryogenic Liquids
Nonliquefied gases that become liquids at low temp
Liquefied compressed gases
becomes liquid to large extent in containers at ambient temperatures, at pressures 25-1500psig
o Nitrous oxide, carbon dioxide
Which organizations regulate manufacturer, marking, labeling, etc of medical gas cylinders?
DOT - Dept of Transport
Transport Canada
Role of Dept of Labor, OSHA?
regulates matters affecting safety, health of employees in all industries
Body of Cylinders
o Steel +/- various alloys added, steel carbon fiber: “3AA”
o Advantages steel carbon fiber: hold more gas than older steel counterparts, lighter weight
o Aluminum for MRI: “3AL,” “3ALM”
o Flat, concave bases with neck fitting with tapered screw threads attached to valve
Function of valve?
Cylinders = Filled, discharged through valve (spindle valve) attached to neck – bronze, brass
–Only removed by cylinder owner
Parts: port, stem, packed or diaphragm valve
Stem of Cylinder Valve
rotated during valve opening/closing
To close valve, stem seals against seat that part of valve body
When valve opened, stem moves upward, allowing gas to flow through port
Port of Cylinder Valve
point of exit for gas, should be protected in transit by covering
Cylinder Packed Valve
Most common
Stem sealed by resilient packing eg Teflon to prevent leaks around thread
AKA direct acting, bc turning stem causes seat to turn
Valve capable of withstanding high pressures
Requires 2-3 full turns to open
Diaphragm Valve
–Closure accomplished by metal-to-metal seal, bonnet nut - clamps one or more circular disks in place
–Disks/diaphragms separate upper, lower stems, may be permanently attached to diaphragms
* Upper stem: actuated by manual/automatic means
* Lower stem: shuts/permits flow through valve
Advantages of a diaphragm valve
opened fully by using ½-3/4 turn, seat does not turn so less likely to leak, no stem leakage can occur bc of the diaphragm
When is a diaphragm valve preferred?***
pressures low, no leaks can be allowed ie flammable gases
Disadvantages of a diaphragm valve?
More expensive
Handle/Handwheel
o Open (counterclockwise) or close (clockwise) valve
o Variety of shapes
Ex: hexagonal opening (CUHA) one end opens tank, other fits hexagonal nut of valve (risk of loosening packing nut instead of opening tank)
o Good practice: handle attached to each AM, check cylinder can be opened before use
o Each large cylinder has permanently attached handwheel that uses a spring and nut to hold firmly in place
Pressure Relief Devices
- Rupture Disc
- Fusible Plug
- Combination Rupture Disc/Fusible Plug
- Pressure Relief Valve
Pressure relief: rupture disc
non-reclosing device with disc held against an orifice
When predetermined pressure reached, disc ruptures allows cylinder contents to be discharged
Pressure opening: orifice against which disc functions
Used in some air, CO2, CO2-O2, He, N2O, He-O2, N2, O2 cylinders
Protects against excess pressure DT high temperature or overfilling
Rated Burst Pressure in Rupture Disc
Pressure at which disc designed to burst; determined by material, thickness, shape of disc, diameter of pressure opening
Fusible Plug
thermally operated, non-reclosing pressure-relief device with plug held against discharge channel
Offers protection from excessive pressure caused by high temperature but not from overfilling
Fusible plug yield temperature
temperature at which fusible material becomes sufficiently soft to extrude from its holder so that cylinder contents discharged
* Fusible plug with yield temperature of 212*F sometimes used on certain nitrogen, air cylinders
Combination Rupture Disc/Fusible Plug
prevent bursting at predetermined pressures unless temperature high enough to cause fusible material to yield
Devices with yield temperature of 165F cylinders of: air, oxygen, nitrogen, nitrous oxide, He, He-Ox, CO2, CO2-O2 mix
*Bc function only in presence of excessive heat/pressure, do not offer protection from high pressure DT overfilling
Pressure Relief Valve
spring-loaded device designed to reclose, prevent cylinder contents from being discharged after normal pressure has been restored
Set pressure: pressure at will start to discharge, marked on valve
Generally more susceptible to leaks
Found on air, He, O2, nitrogen, He-O2 mix, CO2, CO2-O2 mix cylinders
Conical Depression
o Above safety relief valve
o Receives retaining screw of yoke
o Must be distinguished from safety relief device if retaining screw tightening into safety relieve device by mistake, can be
Where is the noninterchangeable safety system located?
Btw cylinder valve, pressure regulator
Pin Index Safety System
Holes on valve - port will not seat unless pins/holes aligned
Holes numbered from R to L (clockwise direction)
1 = R, 6 = L when facing valve
PISS: O2?
2, 5
PISS: air?
1, 5
PISS: N2O
3, 5
PISS: Nitrogen
1, 4
PISS: Cyclopropane?
3, 6
Bull Nose Connections
Ensure appropriate connections with large tanks, btw cylinder valve and pressure regulator
Outlet threads mesh with nut, nut may be tightened -> nipple seats against valve outlet
* Gas channel of valve aligns with channel of nipple
What are the bull nose connections indexed by?
diameter, thread size, right/left hand treading, external/internal threading, nipple seat design
E Tanks - O2
Empty cylinder = 14#, 1900psig, 660L
H Tank - O2
Empty cylinder = 119#, 2200psig, 6900L
How measure quantity remaining in a cylinder for non liquefied gas?
Pressure gauge
B tank - O2 pressure
1900psi, 200L
D tank - O2 pressure
1900psi, 400L (D doubles B)
M tank - oxygen
3450L, 2200psig
How measure quantity of gas left in cylinder of liquified gas?
Weight of cylinder
Why: If the liquid remains when withdrawal stops, cylinder pressure will slowly increase to its original level as temp rises WHY CANNOT USE PRESSURE
Why can’t you use pressure to determine the contents of a cylinder containing N2O?
Pressure depends on vapor pressure of liquid -> Pressure remains nearly constant (with constant temperature) until all liquid has evaporated, after which pressure declines until cylinder exhausted
During use: temperature not likely to remain constant
* Evaporation of liquid, expansion of gas requires energy in form of heat, which is supplied by liquid in cylinder = cooling (vaporizers)
* If outer surface of liquefied gas cylinder becomes cold as gas discharged, residual liquid remains in cylinder ie cylinder should feel cold
* As temp falls, vapor pressure of liquid also decreases so have progressive fall in pressure accompanies release of gas from cylinder
* If the liquid remains when withdrawal stops, cylinder pressure will slowly increase to its original level as temp rises
What is a cylinder’s service pressure?
max pressure to which cylinder may be filled at 70*F
testing: minimum 1.66x service pressure
Filling of Cylinders
Pressure in filled cylinder @ 70*F may not exceed service pressure on cylinder except for some nonliquefied, nonflammable gases, which may be allowed an additional 10%
Filling of cylinders for liquefied gases
Pressure in cylinder at 130F may not exceed 1.25x max filling pressure at 70 except N2O, CO2
How prevent cylinder containing liquefied gas from being overfilled?
maximum amount of gas allowed defined by a filling density (filling or fill ratio) for each gas
Filling density NOT the same as volume of the full cylinder occupied by the liquid phase, N20 = 68% vs in full cylinder liquid phase 90-95% of vol
What is filling density?
percent ratio of the weight of gas in a cylinder to the weight of water that the cylinder would hold at 60F
Coloring of Cylinders
o Top/shoulder (part sloping up to neck) or entire cylinder with assigned color
Nonfading, durable, water-insoluble paint
o >1 gas: colors applied so that each seen from top
o Corresponding color on valve protection caps, hoses, connectors, knobs, gauges on medical equipment
o International code: oxygen is white, air black and white (different in US)
o Color standardization not applicable in areas where specialty gases (eg calibration) used
Ex: calibration of airway gas monitor
o Labels more reliable
Markings on a Cylinder
o Permanently stamped on the shoulder, required by DOT and TC
o Ex: DOT-3A2015
DOT specification = 3A
service pressure is 2015 psig at 70F
8642 - serial number
XYZ -manufacturer
JCN -owner’s symbol
o + sign: authorized to be charged up to 10% excess of marked service pressure
PLUG or SPUN
SPUN
bottom end closed by spinning
PLUG
closure produced by spinning, drilling, plugging
The following is a label on a cylinder. What is denoted by each set of numbers?
DOT-5B2425
8651
ABC
EMP
Top line - DOT specification is 5B, service pressure is 2425 at 70*
Second line - serial number
ABC - manufacturer
EMP - owner’s symbol
Labeling
abel or decal required on side, ideally on shoulder but not so that covers permanent marking
o Hazard class – oxidizer, nonflammable gas, flammable gas
o Name of gas
o Signal word – DANGER, WARNING, CAUTION
o Statement of hazard: dangers with anticipated use/handling + measures to avoid injury/damage
o Name/address of manufacturer/distributor
o Statement about contents
Usually volume in L at 70F, +/- cylinder weight when full and empty
o Expiratory date
DANGER
Immediate Hazard
WARNING
less than immediate
CAUTION
no immediate hazard
What is the hazard class symbol for an oxidizer?
Yellow sign, circle under flames
What is the hazard class symbol for a flammable gas?
Red sign, flames
What is the hazard class symbol for nonflammable gas?
Green gas cylinder
Tags
o Three sections, often same color as cylinder
FULL: detach when cylinder put into service
IN USE: remove when empty
EMPTY
o Goal: amt of cylinder contents, NOT identification
What is the most easily damaged part of the gas cylinder?
The valve
What are the temperature limitations of cylinders?
No part of the cylinder subjected to temp >54C (130F), below -7C (20F)
Avoid proximity to radiators/heat ducts, exposure to extreme cold
Snow, ice accumulation on cylinder: thaw at room temp or water <130*F
What is an adiabatic process?
heat neither lost to or gained from environment
How is an adiabatic process relevant to gas cylinders?
OPEN VALVE SLOWLY
If gas passes quickly into space btw valve, yoke or regulator – rapid recompression in space will generate large amounts of heat
* Particles of duct, grease, etc in space= flash fire, explosion
* Opening valve slowly prolongs time of recompression, permits some of the heat to dissipate
What is true about transfilling?
- May affect purity
- When small cylinder transfilled from large cylinder containing gas at high pressure, rapid recompression of gas in small cylinder may cause temperature rise sufficiently= FIRE
- Risk charging with gas other than what originally in cylinder - dangerous mixture
- Missed inspections of safety devices etc that would be caught by manufacturer
What are the requirements of medical grade oxygen?
Medical grade oxygen required to be 99% pure
Of remaining 1% (10,000ppm):
* <300ppm CO2
* <10ppm CO
* <5ppm oxides of nitrogen
* No other contaminants specifically excluded from other 9685ppm potential to have dangerous amts of other compounds, not be in violation of existing standards
Liquid Oxygen Tanks
Stationary unit refilled by gas supplier as needed
Smaller portable units filled from stationary unit
o Broader, shorter than cylinders – amt of gas determined by weight
o Pressure relief device, means to limit amount of liquid oxygen contained
When not in use pressure in container controlled by venting excess gas to atmosphere
Limits time oxygen can be stored in portable unit
What government org oversees liquid oxygen tanks?
DOT
What are required markings on a liquid oxygen container?
Specification number, service pressure for which container designed, identifying mark of original container owner, serial number
Date of manufacture, symbol to identify inspector
Storage of liquid oxygen tanks
Cool, well-ventilated areas away from heat sources, corrosive atmospheres
Upright position
What are three unique risks of liquid oxygen?
- cryogenic burns
- Creation of an oxygen enriched environment, increased fire hazard
- Valves may freeze if not kept free of moisture
What organizations oversee pipeline systems?
o National Fire Protection Association
o Compressed Gas Assoc
o Canadian Standards Assoc
o International Standards Organization
o State/local codes
At what PSI are gases other than N2, instrument air pumped?
160psi
What are the three ways in which a facility can supply oxygen?
- Gaseous supply
- Liquid supply
- Oxygen concentrators
Liquid Supply
Best for systems with constant demand
less expensive, more convenient
* Store at ground level, location where potential ignition sources minimal
* Special insulated vessels to keep <-297*F, prevents evaporation
o Thermos bottle with outer, inner metal jacket
o Metal jackets separated by insulation, layer near vacuum to retard heat transfer from exterior
MOA Liquid oxygen storage
- Usually kept cold by latent heat of vaporization as gaseous oxygen removed, temp falls (think vaporizers)
- Gaseous oxygen drawn off as needed, passed through heater (vaporizer) to bring up to ambient temp, raise pressure
o Coil, tube, or mesh heated via electricity or hot water - Some amt of uncontrolled evaporation DT continuous absorption of heat from surroundings, liquified gas evaporates if left standing unused for long time, significant amt of oxygen lost
o Liquid supply best for systems with
What is medical air?
defined by NFPA as air that meets US Pharmacopoeia (USP) quality standards
How medical air made?
Manifold cylinders
Oroportioning device that mixes gases from oxygen/N2 cylinders
motor-driven compressors
Compressors to create medical air
take in ambient air, compresses to above working pressure, supplies to one or more receivers – withdrawn as needed
* Pressure relief valve
* Automatic drain, slight glass to permit visual checking that operating ok
* Pressure gauge
Important considerations for air compressors
Intake location for compressors important – air as free of contamination as possible from dirt, fumes, odor
Water content must be reduced via aftercooler (air cooled, condensed moisture removed) or running air through dryer
Instrument Air
different than medical air, doesn’t have to meet same requirements
Piping systems: main lines
pipes coming source to risers, branch lines, or both
Piping systems: risers
vertical pipes connecting main line with branch lines on various levels of facility
Piping systems: branch (lateral) lines
piping system that services room, group of rooms on same level of facility
What piping diameter is required for oxygen vs other gases?
Oxygen = 1/2”
Other gases = 3/8”
Where are pressure relief valves located in a piping system?
set at 50% above normal line pressure downstream of regulators, upstream of shut off – prevents build up if shutoff closed
Shut Off Valves
isolation in event of a problem, maintenance, repair, testing, expansion, etc
o Manual: accessible to anyone, visible
o Service: authorized personnel only
Placement of shut off valves
Outlet from supply source, isolates entire supply source
Main supply: manual shut off near entry to building
Each riser: manual shut off valve adjacent to connection to main supply line
Each branch line, except in anesthetizing locations/other vital life support
* Critical locations = service shut off valve whether lateral branches off riser
* Manual valve immediately outside each critical location so shutting off supply to one location will not affect others
What is a terminal unit?
Point in piped gas distribution system at which user normally makes connections, disconnections
What are the parts of a terminal unit?
base block (attached to pipeline distribution system)
primary valve
secondary valve
gas-specific connection point (socket assembly) face plate
Primary Valve on a Terminal Unit
o Opens, allows gas to flow when male probe inserted
o Closes automatically when connection broken, prevents gas loss when removal component disconnected
o Not a unidirectional valve – permits flow in either direction
o When in place, secondary valve stays open
Secondary Valve on a Terminal Unit
o When primary valve removed, gas flow shut off
o Open when primary valve in place
Socket Assembly
o Receptor for non-interchangeable gas-specific connector part of or attached to base block incorporated into each terminal unit
Female component = outlet connector
Male component = inlet connector
DISS, quick connect systems
Diameter Index Safety System
noninterchangeable connections for medical gas lines at <200psi
Body, nipple, nut
MOA DISS
Body, nipple, nut
Two concentric, specific bores in body; two on concentric, specific shoulders on nipple
* Small bore mates with small shoulder
* Large bore large shoulder
For noninterchangability btw different connectors: two diameters on each part vary in opposite directions so as one diameter increases, other decreases
ASTM: every AM must have DISS fitting for each pipeline inlet
Quick Connectors
Proprietary quick connect systems, allows apparatuses to be connected/disconnected by single action without tools/undue force
More convenient, leak more than DISS
Gas-specific male, female components
Releasable spring mechanisms locks components together – different shapes/spacing of mating portions for different gases
Face Plate
permanently marked with name +/- symbol of gas that conveys, +/- identifying color
Types of Terminal Units
Wall outlets
Ceiling mounted hoses
Ceiling mounted pendants
Ceiling Column
Wall Outlets
small rooms, equipment connected near wall
Ceiling mounted hoses
I hope this is self explanatory but if not, think PCVRH
Ceiling mounted pendants
keeps wires, hoses from cluttering floor, easily moved to various positions
Ceiling column
similar to pendant, less versatile with respect to positioning
Risk of hitting head, tough to reach if short, difficult to assess hoses inside column
Hoses
connect AM, other apparatus to terminal units
o Permanently attached, noninterchangeable connector
o Color-coded with name +/- chemical symbol of contained gas on each connector
o Keep away from heat source (OR lights) – potential to cause rupture, keep off floor
o Gentle curve
o Over time, can weaken, swell, or crack – inspect routinely
If you need more hose length, is it preferred to have one long hose or multiple short hoses?
o One long hose»_space;> several connected to create long hose
Resistance may interfere with gas flow
Leaks: most occur in connectors or where connector fits into hose
What is the pressure for a gas mixture during a standing pressure test?
20psi
What is the pressure for nitrogen during a standing pressure test?
30psi
What is the pressure for a N2O during a standing pressure test?
40psi
What is the pressure for oxygen during a standing pressure test?
50psi
What is the pressure for medical area during a standing pressure test?
60psi
Operational pressure tests for oxygen, N2O, medical air
Oxygen, N2O, medical air: outlets deliver 100L/min with pressure drop <5psi at static pressure of 50-55psi
Operational pressure tests for nitrogen, instrument air
Nitrogen outlets, instrument air: 140L/min, pressure drop <5psi at static pressure of 160-185psi
Oxygen Concentrators
o Pressure swing absorption (PSA) technology, incereases oxygen concentration by adsorbing N2 onto molecular sieve that allows oxygen, trace gases (esp argon) to pass through
What is the concentration of oxygen achieved using oxygen concentrator? Product name?
Oxygen concentration 90-96%, name = Oxygen 93% USP
Molecular sieve used by oxygen concentrator
Inorganic silicate = Zeolites - Belongs to class of crystalline compounds
MOA Sieve
System of precisely arrayed cavities, pores that are uniform in size within each granule – molecules readily adsorbed or completely excluded
Molecular size, polarity of gas determine whether retained by sieve material
Zeolite’s affinity for water
STRONG
* During use, water in sieve will displace other molecules, reducing capacity to adsorb nitrogen
* Not affected by room humidity during normal operation
Sieve at entrance to bed or column adsorbs moisture, returned to atmosphere during purge phase
Beds must be kept sealed from atmosphere to prevent moisture migration into them
what is the benefit of pressure swing adsorption?
allows for continuous output of oxygen-enriched gas via two sieve beds in sequential adsorption-desorption process
As one sieve adsorbs N2 under pressure, other is desorbed/purged
Output depends on size of installation
basic MOA of oxygen concentrator
o Pressurized air passes through sieve bed: O2 passes through freely; N2, CO2, CO, water vapor, hydrocarbons trapped
Trapped molecules = desorbed (released) by venting sieve to atmosphere, s adsorptive force
Regeneration of sieve via purging with some product gas
More Thorough Description of Gas Flow through A Concentrator
o Filters at inlet remove particles, bacteria; sound reduced by muffler (1)
o Compressor receives filtered air, compresses it to higher pressure (2)
o Heat exchanger (coiled tubing) cools gas (3)
o Some concentrators: compressed gas will enter reservoir (surge tank) (4) – dampens pulsations generated by compressor
o Valves (6) (electrically or pneumatically controlled) direct gas flow through concentration
Two zeolite beds: continuous oxygen production, sieve regeneration (7)
o Product tank functions as reservoir of product gas (8)
May also serve as source of purge gas
o Pressure regulator (9): reduce pressure of gas flowing to outlet to lower, more constant pressure
o Check valve btw pressure regulator, outlet prevents room air from being sucked into sieve bed when concentrator off
o Filter near outlet: prevents sieve material, bacteria, other matter from contaminating outflow
o Status indicator required by US – low oxygen concentration in product gas
Oxygen Concentrator Operation
o 2.5-19min once turned on to reach maximum concentration
o Concentration process becomes less efficient if FR increases above optimum level
Applications of an oxygen concentrator
o Domicilary use: compact, lightweight – easy delivery, transport
o Remote locations: when pressurized oxygen, liquid oxygen supply unavailable, unreliable or prohibitively expensive
Field hospitals, disasters, etc
o Source of oxygen supply for pipeline systems
Large-scale oxygen concentrators – main supply for pipeline systems or pipeline supply during shutdown
* Fill cylinders
Reservoir usually supplied by number of concentrators in parallel
Need reservoir supply that automatically supplies system if concentrator malfunctions or falls [O2] below present minimum
Argon does not alter flow characteristics
What are advantages of an oxygen concentrator?
o Cost: product gas less expensive; depends on cost of concentrator, other means of supplying oxygen, electricity, maintenance
o Contaminant filtration: airborne contaminants filtered by molecular sieve, released back into atmosphere
o Compatible with IR, galvanic, paramagnetic gas analyzers (not adversely affected by argon)
o Reliable
o Simple: no dependence on compressed/liquified gases and assoc delivery problems
What are disadvantages of an oxygen concentrator?
o Maintenance: regular servicing required, esp for compressor
Impt to clean/replace air intake filters
o Max O2 yield ~96%
What are the main three hazards with oxygen concentrations?
o Fires
Risk of ignition – keep away from heat, flames, overheated electrical connections, loose connections, oil, grease
o Water Contamination
Humidity not problematic under normal conditions
Very high humidity: oxygen concentration in product gas to be lowered
o Contaminated intake air: not likely to be contaminated by fumes, water, atmospheric pollutants -> damage sieve medium, premature sieve exhaustion
