SCIENCE / MEDICINE : Microwaves Used to Sterilize

Researchers at the National Institute of Standards and Technology in Gaithersburg, Md., have developed a way to use microwaves to sterilize medical, dental and scientific instruments in seconds rather than hours.

Conventional sterilization usually requires that instruments be subjected to hours of steam heat inside the equivalent of a pressure cooker. Repeated treatments gradually destroy rubber and plastic fittings, however, as well as blunting the sharp edges of dental drills and softening metals by annealing them. The microwave method avoids this and is both cheaper and faster than conventional methods, researchers say.

Instruments are placed in an airtight container inside an ordinary microwave oven. Some air is pumped out of the container, leaving a partial vacuum, and the oven is turned on. The microwaves cause the remaining atoms of air to be ionized, or electrically charged, producing a gas plasma that kills microbes of all kinds. The plasma also prevents the arcing that normally occurs when metal objects are placed in a microwave.