Gas Supplies Flashcards
How should large and small cylinders be stored
Inside (Away from temp fluctuations)
Separate storage (full and empty, explosive and non-explosive, medical and non-medical)
Vertical (Large)
Horizontal (Small)
How do gas cylinders withstand high pressures
Made of
- Carbon Steel
- Manganese steel
- Aluminium alloy
But do not prevent risk of explosion if dropped on a hard concrete surface
What are the colours of cylinders as per the international standards of colours for medical gases (ISO/R32)?
SHOULDER COLOURS
Entire shoulder to top O2: White N2O: Blue CO2: Grey Helium: Brown Cyclopropane: Orange
Half shoulder
Medical air: Black / White
Entonox: Blue / White
Heliox: Brown / White
(Might be different in the USA)
For which gas cylinders is there a risk of explosion and why
O2
N2O
Entonox
All support combustion§
How do you know when the cylinder was last examined
Plastic disc at the top of the cylinder –> the color and shape of which denotes the year the cylinder was last examined
How are cylinders examined and what is the interval for examination
Every 5 - 10 years a cylinders is examined and tested. This includes an internal examination with an endoscope, so that faulty ones are withdrawn from use
Where are the safety precautions visible on the cylinder
On an identification label at the top of the cylinder
Why do rising temperatures in summer not cause explosions
Cylinder design is for pressures well above their normal working range (MAx P is 65 - 70% higher than its working pressure)
Why should the cylinder valved be opened momentarily before connection to the anaesthetic machine
TO blow out any dust or other material that might have lodged at the outlet of the cylinder which might otherwise enter the anaesthetic apparatus
Why should the cylinder valve be opened slowly once attached to the anaesthetic apparatus?
TO avoid adiabatic heating
Adiabatic process occurs when a system does not exchange heat with its environment. Heat is neither added nor removed from the system.
The three gas laws describe the behaviour of a gas when one of three variables is kept constant: Temp (Boyles), Pressure (Charles’) and Volume (3rd gas law). For these condition to apply, heat energy is required to be added or taken from a gas as the change occurs.
The state of a gas can also be altered without allowing the gas to exchange heat energy with its surroundings, and this is called an adiabatic change
Describe the structure and function of a cylinder manifold
Variable numbers of large cylinders on either side of the manifold.
1 side in use at a time
Manifold converts cylinder pressure of 13700 kPa to 1000 kPa and thereafter to pipeline pressure of 410kPa.
When 1 side runs empty, the pneumatic shuttle mechanism which is held at extreme positions magnetically, switches automatically to the other bank of cylinders automatically.
Electric warning devices are activated by the change over.
(Bank up bank of cylinders is present in case of failure of change over)
What happens if the Vacuum Insulated Evaporator with liquid oxygen supply fails.
There is usually a backup cylinder bank with a manifold. An automated changeover mechanism is present in the case of VIE supply failure and is accompanied by various types of alarms and notification systems.
How does a Vacuum Insulated Evaporator work?
Critical temperature of O2 is - 119 deg C (Cannot exist as a liquid above this temperature)
Vacuum Insulated Evaporater stores O2 below this temp as a liquid, at around -160 deg C.
Large quantities of O2 can be stored which is more economical than O2 cylinder banks.
Vapour Pressure O2 at -160 deg C is ± 7 bar. O2 vapour is taken from the top of the vessel and passed through a superheater coil —> Pressure regulator to achieve pipeline pressures of 4.1 bar. As O2 exits, more O2 liquid vaporises —> cooling the system through loss of the latent heat of vaporisation. To keep constant temperature, a supplementary source of heat is required and is provided by a PRESSURE RAISING VAPORISER. This vaporiser sense the pressure in the system and controls the flow of liquid O2 in the pressure raising vaporiser heating component until the vapour pressure of 7 bar is re-established.
If no O2 is used, the temp rises over a week and there is a safety release valve which will release excess O2.
What cylinder pressure is entonox stored at
137 x 100 kPa
What happens when an entonox cylinder is cooled to temps below -5.5 deg C. How can this hazard be prevented
A liquid phase containing 80% N2O and 20% O2 forms with a gas layer above containing predominantly O2. if the cylinder is used during this time, the O2 is depleted (with minimal N2O in effect). Eventually both liquid and gas phases will contain minimal O2.
Prevention = ‘dip tube’ which draws off any liquid phase first. However, this is only a secondary safety mechanism and entonox should be stored at > 10 deg C
What are the various ways of storing and supplying medical air in hospitals
- Cylinders with manifold
2. Central compressor plant
