Moist Heat Sterilisation

Question 1

Define autoclaving

Answer 1

Moist heat with temp over 100 degrees under pressure
Organisms are killed via, temperature, hydration and time

Question 2

Define superheated steam and does it release sensible or latent heat

Answer 2

Water in the vapour phase, behaves like a gas
If the temp decreases the pressure also decreases
Releases only sensible heat

Question 3

Define supersaturated steam and does it release sensible or latent heat

Answer 3

The liquid phase made up of small droplets of water held in a suspension of convection currents
Both sensible and latent heat, in the absent of condensation releases only sensible heat

Question 4

Define dry saturated steam and does it release sensible or latent heat

Answer 4

Exists on the phase boundary
if the temperature deceases it will condense
Releases both sensible and latent heat

Question 5

Name the two main designs of autoclaves

Answer 5

Large scale sterilisers
Portable bench top sterilisers

Question 6

What are the advantages of a heated outer jacket?

Answer 6

Prevent heat loss (even heat distribution)
Can also be used for calling down the autoclave

Question 7

What are the problems that sterilising can occur through?

Answer 7

Superheated steam (too hot, too far away from the phase boundary)
- too dry steam supply
- overheating steam jacket
- excessive pressure reduction
- hydration of over dried cotton fabrics

Question 8

What are the advantages of portable bench top sterilisers?

Answer 8

Easy to use
Works well for small no of items
Doesn’t suffer from overheating
But insufficient if the vessel is too large - can’t generate steam at large volumes
Need to ensure it is completely saturated with steam - as air will affect the sterilisation process

Question 9

Is an unjacketed bench autoclave controlled by pressure or temperature

Answer 9

Controlled by pressure only

Question 10

Is a jacked autoclave controlled by pressure or temperature

Answer 10

Controlled by pressure and temperature

Question 11

What does sensible heat result in?

Answer 11

Results in a change in temp

Question 12

What does latent heat result in?

Answer 12

Results in a change in the physical state, not a change in temp

Question 13

Define a porous load autoclave

Answer 13

Filled with a vacuum pump to remove air before adding steam

Question 14

Define gravity displacement autoclave and what is it not suitable for

Answer 14

Steam added from top, air is removed at the bottom
not suitable for porous items (air could become entrapped in packaging or material)
Suitable for media, water, pharmaceutical products, waste and non-porous material

Question 15

Define the three stages of operation

Answer 15

Air removal and steam admission
Heating up and expose
Drying and cooling

Question 16

What three factors play a role in moist heat sterilisation?

Answer 16

1) Release of heat
2) Hydration
3) Penetration