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Dry heat Sterilization method
Dry heat sterilization typically involves exposing an item to a temperature of 170°C under normal air pressure for around an hour. That time period ensures that even the most resistant spores get killed off via oxidation of their cellular components
These methods consist of
- Red heat:Sterilization is done by holding materials in a bunsen burner flame until they become red hot. It is used to sterilize inoculation, straight wires, wire loops, tips of forceps and spatulas
- Flaming:This is a very quick simple method of killing microorganisms on an inoculating loop or needle. The loop or needle is held inside a flame for a few seconds to bring it to redness and then cooled. Once cool, the loop or needle can be used for various culture manipulations.
- Hot air ovens use extremely high temperatures, in a special oven, over several hours to destroy microorganisms and bacterial spores. The ovens use conduction to sterilize items by heating the outside surfaces of the item, which then absorbs the heat and moves it towards the center of the item.
- Incineration involve complete burning of the substance into ash in an incinerator
Method |
Principle/Conditions |
Advantages |
Disadva |
Uses |
Dry Heat |
• Thermal inactivation: destroys by oxidation |
• Non-corrosive |
• Less effective than moist heat; • Requires longer times and/or higher temperatures |
• Materials that are damaged by, or are impenetrable to, moist heat |
Hot Air Oven |
• 160-180oC for 2-4 hours |
• Penetrates water-insoluble materials (e.g., grease and oil) • Less corrosive to metals and sharp instruments than steam |
slow diffusion, penetration • Loading, packing critical to performance • Not suitable for reusable plastics |
• Anhydrous materials, such as oils, greases and powders • Laboratory glassware, instruments • closed containers |
Red-heat Flame |
• Oxidation to ashes (burning) |
• Rapid |
• Initial contact with flame can produce a viable aerosol • Possibility of accidental fire |
• Inoculating loops, needles |
Incineration |
• Oxidation to ashes (burning) • 1-60 minutes: temperatures may exceed 1000?C |
• Reduces volume of waste by up to 95% |
• Improper use may lead to emission of pathogens in smoke • Requires transport of infectious waste • Excess plastic (>20%) content reduces combustibility |
• For decontamination of waste items prior to disposal in landfill |