Sterilization Methods: Hot Air Oven vs. Autoclave

 
Hot air oven (Dry heat Sterilizer)
 
Most widely used method of sterilization by dry heat.
It is electrically heated and is fitted with a fan to ensure
adequate and even distribution of hot air in the chamber.
It is also fitted with a thermostat which maintains the
chamber air at a chosen temperature.
Holding temperature and time of 160°C 
for 2 hours.
 
Hot air oven (Dry heat Sterilizer)
Materials sterilized:
o
Glassware - syringes, petri dishes, flasks, 
pipettes and test
tubes.
o
Surgical instruments - scalpels, forceps, etc.
o
Chemicals such as liquid paraffin, fats, glycerol, oil, and
glove powder, etc.
 
Hot air oven - precautions
 
Overloading of hot air oven should be avoided.
Material should be arranged in a manner so that free circulation of air is
maintained.
Material to be sterilized should be dried completely.
Cotton plugs should be used to close the mouths of test tubes, flasks, etc.
Paper wrapping of the items should be done.
Any inflammable material like rubber (except silicone rubber) should not be
kept inside the oven.
Oven must be allowed to cool for two hours before opening the doors, since
the glassware may crack by sudden cooling.
 
Hot air oven - Sterilization control
 
Biological indicator: Spores (10
6
)
o
 
Bacillus atrophaeus - 
to check the effectiveness of
sterilization by dry heat. Earlier, non-toxigenic strain
of 
Clostridium tetani was used.
o
Spores should be destroyed if 
the sterilization is done
properly.
Physical control: For example, digital displays on the
equipment displaying temperature and time.
 
 Autoclave
 
Autoclave comprises of three parts
 Pressure chamber
Lid
Electrical heater.
 
Horizontal autoclave
and  Vertical autoclave
 
Sterilization Conditions
 
Autoclave can be set to provide higher temperatures by adjusting the pressure
provided to the vessel.
o
121
C for 15 minutes at pressure of 15 lbs psi.
o
126
C for 10 minutes at pressure of 20 psi.
o
133
C for 3 minutes at pressure of 30 psi.
 
Uses of Autoclave
 
Surgical instruments
 Culture media
 Autoclavable plastic containers
 Plastic tubes and pipette tips
 Solutions and water
 Biohazardous waste
 Glassware (autoclave resistible).
 
Precautions to be taken
 
Autoclave should not be used for sterilizing waterproof materials
Materials are loaded in such a way that it allows efficient steam penetration (do
not overfill the chamber)
Material should not touch the sides or top of the chamber
Clean items and the wastes should be autoclaved separately
 olyethylene trays should not be used as they may melt and cause damage to the
autoclave.
 
Types of Autoclaves
 
Gravity displacement type autoclave: most
commonly used.
Positive pressure displacement type autoclave
 Negative pressure (vacuum) displacement type.
 
Sterilization control
 
Biological indicator: 
Spores of 
Geobacillus stearothermophilus 
(formerly called 
Bacillus
stearothermophilus). S
pores are killed in 12 minutes at 121°C
Chemical indicators
o
 Class I - external pack control, (e.g. autoclave tape)
o
 Class II - equipment control (Bowie-Dick test)
o
 Class IV/V - internal pack control.
Physical control: For example, digital displays on the equipment displaying temperature,
time and pressure.
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References
 
Textbook of Medical Microbiology by Ananthnarayan, Paniker
Textbook of Medical Microbiology by C.P Baweja
Textbook of Medical Microbiology by S. Bhat, A.S.Sastry
Textbook of Medical Microbiology
 by D.R.Arora, Brij bala Arora
 
 
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Hot air oven, also known as a dry heat sterilizer, is widely used for sterilizing glassware, surgical instruments, and chemicals by maintaining a temperature of 160°C for 2 hours. Precautions include avoiding overloading, ensuring proper air circulation, and allowing adequate cooling time. Sterilization control involves using biological indicators like Bacillus atrophaeus spores. In contrast, an autoclave utilizes steam under pressure to sterilize various items at specific temperatures and pressures. It is commonly used for surgical instruments, culture media, plastic containers, and more.


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  1. Hot air oven (Dry heat Sterilizer) Most widely used method of sterilization by dry heat. It is electrically heated and is fitted with a fan to ensure adequate and even distribution of hot air in the chamber. It is also fitted with a thermostat which maintains the chamber air at a chosen temperature. Holding temperature and time of 160 C for 2 hours.

  2. Hot air oven (Dry heat Sterilizer) Materials sterilized: o Glassware - syringes, petri dishes, flasks, pipettes and test tubes. o Surgical instruments - scalpels, forceps, etc. o Chemicals such as liquid paraffin, fats, glycerol, oil, and glove powder, etc.

  3. Hot air oven - precautions Overloading of hot air oven should be avoided. Material should be arranged in a manner so that free circulation of air is maintained. Material to be sterilized should be dried completely. Cotton plugs should be used to close the mouths of test tubes, flasks, etc. Paper wrapping of the items should be done. Any inflammable material like rubber (except silicone rubber) should not be kept inside the oven. Oven must be allowed to cool for two hours before opening the doors, since the glassware may crack by sudden cooling.

  4. Hot air oven - Sterilization control Biological indicator: Spores (106) o Bacillus atrophaeus - to check the effectiveness of sterilization by dry heat. Earlier, non-toxigenic strain of Clostridium tetani was used. o Spores should be destroyed if the sterilization is done properly. Physical control: For example, digital displays on the equipment displaying temperature and time.

  5. Autoclave Autoclave comprises of three parts Pressure chamber Lid Electrical heater.

  6. Horizontal autoclave and Vertical autoclave

  7. Sterilization Conditions Autoclave can be set to provide higher temperatures by adjusting the pressure provided to the vessel. o 121 C for 15 minutes at pressure of 15 lbs psi. o 126 C for 10 minutes at pressure of 20 psi. o 133 C for 3 minutes at pressure of 30 psi.

  8. Uses of Autoclave Surgical instruments Culture media Autoclavable plastic containers Plastic tubes and pipette tips Solutions and water Biohazardous waste Glassware (autoclave resistible).

  9. Precautions to be taken Autoclave should not be used for sterilizing waterproof materials Materials are loaded in such a way that it allows efficient steam penetration (do not overfill the chamber) Material should not touch the sides or top of the chamber Clean items and the wastes should be autoclaved separately olyethylene trays should not be used as they may melt and cause damage to the autoclave.

  10. Types of Autoclaves Gravity displacement type autoclave: most commonly used. Positive pressure displacement type autoclave Negative pressure (vacuum) displacement type.

  11. Sterilization control Biological indicator: Spores of Geobacillus stearothermophilus (formerly called Bacillus stearothermophilus). Spores are killed in 12 minutes at 121 C Chemical indicators o Class I - external pack control, (e.g. autoclave tape) o Class II - equipment control (Bowie-Dick test) o Class IV/V - internal pack control. Physical control: For example, digital displays on the equipment displaying temperature, time and pressure.

  12. References Textbook of Medical Microbiology by Ananthnarayan, Paniker Textbook of Medical Microbiology by C.P Baweja Textbook of Medical Microbiology by S. Bhat, A.S.Sastry Textbook of Medical Microbiology by D.R.Arora, Brij bala Arora

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