Gas Storage

Question 1

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Storage area maintained above 10°C

Answer 1

True

Question 2

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Vertical storage of cylinders

Answer 2

False. Cylinders should be stored horizontally.

Question 3

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Provision of Entonox® by pipeline supply

Answer 3

True

Question 4

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Intermittent use of Entonox®

Answer 4

False. Whilst intermittent use may reduce cooling from latent heat, the nature of Entonox® use makes this unlikely to be feasible.

Question 5

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Inclusion of a dip tube

Answer 5

True. A dip tube ensures that the initial gas drawn off has a minimum oxygen concentration of 20% that has remained mixed in the nitrous oxide. The mixture delivered later has excess oxygen, but lacks nitrous oxide as pain relief.

Question 6

The following can be used to avoid the delivery of a hypoxic mixture from an Entonox® cylinder (true or false):

Re-warming after Entonox® has been stored below its pseudocritical temperature

Answer 6

False. Re-warming would not redress the hypoxic mixture already potentially created, nor necessarily re-vaporize the nitrous oxide as Entonox®.

Question 7

The critical temperature (true or false):

Of oxygen is -160°C

Answer 7

False. The critical temperature of oxygen is -118.6°C.

Question 8

The critical temperature (true or false):

Of Entonox® is 7°C at 137 bar

Answer 8

False. The pseudocritical temperature of Entonox® is -7°C, not +7°C.

Question 8

The critical temperature (true or false):

Of nitrous oxide is 36.5°C

Answer 8

True

Question 8

The critical temperature (true or false):

Of a substance increases with a drop in critical pressure

Answer 8

False. The critical temperature of a substance is fixed and does not vary with changes in pressure.

Question 9

The critical temperature (true or false):

Of a gaseous substance describes the temperature below which a liquid cannot be produced by pressure alone

Answer 9

False. The critical temperature of a substance is a fixed temperature above which the substance cannot be liquefied no matter how much pressure is applied.

Question 10

Regarding gas storage (true or false):

There is a global standard filling ratio for nitrous oxide

Answer 10

A. False. The filling ratio describes the weight of fluid within a nitrous cylinder compared with the weight of the cylinder when filled completely with water. Filling ratio varies with geographical climate; in temperate climates it is 0.75, reduced to 0.67 in hotter climates because the increased vaporization leads to increased pressure within the cylinder.

Question 11

Regarding gas storage (true or false):

Liquid oxygen storage is costly, but convenient

Answer 11

False. Liquid oxygen storage in VIEs is space saving and cost saving.

Question 12

Regarding gas storage (true or false):

A full oxygen cylinder has a gauge pressure of 137 bar when full

Answer 12

True

Question 13

Regarding gas storage (true or false):

Oxygen cylinders are black with a continuous white collar

Answer 13

True

Question 14

Regarding gas storage (true or false):

As high volumes of oxygen from a VIE are used, the supply pressure to the pipeline rises

Answer 14

False. High flow rates from a VIE could potentially lead to a fall in pressure due to latent heat of vaporization, however the pressure raising vaporizer system ensures that pressure is kept fairly constant.

Question 15

Regarding nitrous oxide (true or false):

It can be mixed with air to form Entonox®, via the Poynting effect

Answer 15

False. Oxygen is bubbled through liquid nitrous oxide to form Entonox®. Air is not used.

Question 16

Regarding nitrous oxide (true or false):

It is generally stored as a gas

Answer 16

False. A standard size E cylinder can store 1800 L of nitrous oxide as opposed to 680 L of gaseous oxygen. At a pressure of 52 bar nitrous oxide would liquefy anyway at room temperature.

Question 17

Regarding nitrous oxide (true or false):

Gauge pressure can be a reliable measure of the cylinder content

Answer 17

True. The gauge pressure on a nitrous oxide cylinder can be an accurate measure of cylinder content once all liquid has vaporized, with a pressure below about 52 bar.

Question 18

Regarding nitrous oxide (true or false):

It should be stored in cylinders horizontally

Answer 18

False. Nitrous oxide is stored vertically. Entonox should be stored horizontally to prevent liquefaction.

Question 18

Regarding nitrous oxide (true or false):

It is stored in French blue cylinders

Answer 18

True

Question 19

Regarding the shape of the nitrous oxide isotherm at 20°C (true or false):

Nitrous oxide has a critical temperature of 46.5°C

Answer 19

False. Nitrous oxide has a critical temperature of 36.5°C. This does not relate to the isotherm at 20°C.

Isotherms are lines depicting the effect of temperature and pressure on the physical state of a substance. Each isotherm relates to a different temperature at, above or below the critical temperature.

Question 19

Regarding the shape of the nitrous oxide isotherm at 20°C (true or false):

There is a direct relationship between pressure and volume above the critical temperature of nitrous oxide

Answer 19

False. There is an indirect relationship between pressure and volume above the critical temperature of nitrous oxide.

Isotherms are lines depicting the effect of temperature and pressure on the physical state of a substance. Each isotherm relates to a different temperature at, above or below the critical temperature.

Question 20

Regarding the shape of the nitrous oxide isotherm at 20°C (true or false):

The critical pressure at 36.5°C is 132 bar

Answer 20

False. The critical pressure at 36.5°C is 72 bar. This does not relate to the isotherm at 20°C.

Isotherms are lines depicting the effect of temperature and pressure on the physical state of a substance. Each isotherm relates to a different temperature at, above or below the critical temperature.

Question 21

Regarding the shape of the nitrous oxide isotherm at 20°C (true or false):

Latent heat of vaporization causes a temperature rise as the liquid vaporizes

Answer 21

False. The latent heat of vaporization causes a temperature drop as the liquid vaporizes, but the isotherm relates to the changes which occur at a fixed temperature, 20°C.

Isotherms are lines depicting the effect of temperature and pressure on the physical state of a substance. Each isotherm relates to a different temperature at, above or below the critical temperature.

Question 22

Regarding the shape of the nitrous oxide isotherm at 20°C (true or false):

The nitrous oxide steadily liquefies at a pressure of 52 bar and then demonstrates a clear inflexion point once all the vapour has turned to liquid

Answer 22

True

Isotherms are lines depicting the effect of temperature and pressure on the physical state of a substance. Each isotherm relates to a different temperature at, above or below the critical temperature.