is moist heat sterilisation used for pharmaceutical products?
no
autoclaving
moist heat temp > 100 degrees celsius can only be achieved under pressure, performed In autoclave - similar to domestic pressure cooker but better facilities for control
organisms killed by a combo of temp, hydration, time
properties of steam in a closed container
PV/T = constant
Pressure
volume
temperature
at constant volume pressure varies with temperature
different types of steam
Superheated steam - water in the vapour phase and behaves like a gas, if temp decreases the pressure decreases
supersaturated steam/ wet steam - in liquid phase made up of small droplets of water held in suspension by convection currents
dry saturated steam - exists on the phase boundary, if you lower the temp it will condense ( only one suitable for sterilisation)
factors playing a role in dry saturated steam?
release of heat
hydration
penetration
1.release of heat
sensible heat - when exchanged, results in change of temperature
latent heat - when exchanged, results in change of physical state - there is no temp change
supersaturated steam - releases only sensible heat
superheated steam - releases only sensible heat
dry saturated heat - releases sensible and latent heat
2.hydration
dry saturated steam causes a moist heat reaction - rapid heat transfer
superheated steam causes a dry heat reaction - slower heat transfer
3.penetration
dry saturated steam causes rapid penetration
superheated steam causes poor penetration
design of autoclaves
portable bench top sterilisers
large scale sterilisers
bench autoclaves
easy to se
word well for small number of items
does not suffer from superheating as there is water in the vessel itself
inefficient if vessel gets too large - problems with heat loss and not effective for generating steam at large volumes
large scale autoclaves
use separate steam generator
often have a heated outer jacket - necessary for even heat distribution and cooling after autoclaving
different types of large scale autoclaves
gravity displacement autoclave- steam added from top, air is removed at bottom
porous load autoclave (vacuum assisted) - fitted with vacuum sumo to remove air before adding steam
what does autoclaving do?
Autoclaves are used to sterilize and decontaminate items using pressurized steam to kill microorganisms and spores
stages of operation of autoclaving?
air removal and steam admission
heating up and exposure
drying and cooling - dry using vacuum and or heat from outer jacket and cooling shortens cycle