- Hot air oven
Hot air ovens are
electrical devices used insterilization .The oven utilizesdry heat to sterilize articles. Generally, they can be operated between 50 deg. C to 250/300 deg. There is a thermostat controlling the temperature. These are digitally controlled to maintain thetemperature . Their double walled insulation keeps the heat in and conservesenergy , the inner layer being a poor conductor and outer layer being metallic. There is also an air filled space in between to aidinsulation . An air circulating fan helps in uniform distribution of the heat. These are fitted with the adjustable wire mesh plated trays oraluminium trays and may have an on/off rocker switch, as well as indicators and controls for temperature and holding time. The capacities of these ovens vary. Power supply needs vary from country to country, depending on thevoltage and frequency (Hertz ) used. Temperature sensitive tapes or other devices like those utilizingbacterial spores can be used to work as controls, to test for theefficacy of the device in every cycle.Advantages and disadvantages
They do not require water and there is not much pressure build up within the oven, unlike an
autoclave , making them safer to work with. This also makes them more suitable to be used in alaboratory environment.They are much smaller than autoclaves but still as efficacious.They can be more rapid than an autoclave and higher temperatures can be reached compared to other means.As they usedry heat instead ofmoist heat , some organisms likeprions , may not be killed by them every time.Usage
A complete cycle involves heating the oven to the required temperature, maintaining that temperature for the proper time interval for that temperature, turning the machine off and cooling the articles in the closed oven till they reach room temperature. The standard settings for a hot air oven are:
*1.5 to 2 hours at 160 °C (320 °F)
*6 to 12 mins at 190 °C (374 °F)....plus the time required to preheat the chamber before beginning the sterilization cycle. If the door is opened before time, heat escapes and the process becomes incomplete.Thus the cycle must be properly repeated all over.These are widely used to
sterilize articles that can withstand high temperatures and not get burnt, like glassware, powders, paraffin. Linen gets burnt and surgical sharps, lose their sharpness.References
# Textbook of Microbiology by Prof. C P Baveja, ISBN 81-7855-266-3
# Textbook of Microbiology by Ananthanarayan and Panikar, ISBN 81-250-2808-0
# http://www.tpub.com/content/medical/14274/css/14274_146.htm
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