Moist heat sterilisation

Question 1

What is Superheated steam?

Answer 1

Water is in the Vapour phase (behaves like a gas)

If temperature decreases then so does pressure

Question 2

What is Dry Saturated steam?

Answer 2

Exists only on the phase boundary

If temperature decreases then it will condense

Question 3

What is Supersaturated (wet) steam?

Answer 3

Wet steam (is in liquid phase)

Made up of small droplets of water held in suspension by convection currents

Question 4

Which type of steam is the only one suitable for sterilisation?

Answer 4

Dry Saturated steam

Question 5

Bench autoclave

Answer 5

Easy to use

Works well for a small number of items

Does NOT suffer from superheating (as there is water in the vessel itself) i.e more steam is made if temp rise

Inefficient if vessel gets too large

Question 6

Large scale autoclave

Answer 6

External supply of steam
- Shorter cycle times (steam available immediately)

Very large autoclaves have heated outer jacket to:

• Prevent heat loss
• Assist in cooling

Heating coils in external boiler prevent wet steam formation

Question 7

What role do the heating coils play in the large scale autoclave?

Answer 7

Prevent wet steam formation

Question 8

What role does the heated outer jacket in large scale autoclaves play?

Answer 8

Prevents heat loss

Assists in cooling

Question 9

What are the problems with superheated steam?

Answer 9

Steam supply too dry
Overheating of steam jacket
Excessive pressure reduction (reduction of pressure results in generation of heat)

Question 10

What problems does air cause in an unjacketed bench autoclave?

Answer 10

Usually controlled by pressure only

Air leads to lower temperature

Question 11

What problems does air cause in a jacketed bench autoclave?

Answer 11

Usually controlled by pressure and temperature

Air leads to superheating

Question 12

Describe layering and how it affects autoclaving

Answer 12

The density of air is 2x higher than the density of steam
Air forms layer in upright position
Air will be cooler

Question 13

What is sensible heat?

Answer 13

Results in change of temperature

Question 14

What is latent heat?

Answer 14

Results in change of physical state (does not change temperature)

Question 15

What type(s) of heat does Superheated steam release?

Answer 15

Both sensible and latent

In absence of condensation will release only sensible heat

Question 16

What type(s) of heat does Dry Saturated steam release?

Answer 16

Both sensible and latent

Question 17

What type(s) of heat does Supersaturated steam release?

Answer 17

Only sensible

Question 18

Describe the hydration and penetration of Dry Saturated steam

Answer 18

Hydration: Moist heat reaction (hydration, rapid heat transfer)

Penetration: Rapid penetration (condensation, vaccum)

Question 19

Describe the hydration and penetration of Superheated steam

Answer 19

Hydration: Dry heat reaction (oxidation, slower heat transfer)

Penetration: Poor penetration (no condensation, no vaccum)

Question 20

Why is oxidation less effective at inactivating spores?

Answer 20

It requires

• Higher temperatures
• Longer periods of time