downward displacement and the prevacuum, high-temperature autoclaves. Downward Displacement Autoclave.—In the downward (gravity) displacement autoclave, air in the chamber is forced downward from the top of the chamber. The temperature in the sterilizer gradually increases as the steam heats the chamber and its contents. The actual timing does not begin until the temperature is above 245EF (118EC). Prevacuum, High-temperature Autoclave.— The prevacuum, high-temperature autoclave is the most modern and economical to operate and requires the least time to sterilize a single load. By use of a vacuum pump, air is extracted from the chamber before admitting steam. This prevacuum process permits instant steam penetration to all articles and through all cotton or linen dry goods. The sterilization time is reduced to 4 minutes. The temperature of the chamber is rapidly raised and held at 274EF (134EC). The cycle is timed automatically. Sterilizing Times.—If the temperature is increased, the sterilization time may be decreased. The following are some practical sterilization time periods.  3 minutes at 270EF (132EC)  8 minutes at 257EF (125EC)  18 minutes at 245EF (118EC) All operating rooms are equipped with high-speed (flash) sterilizers. Wrapped, covered, opened instruments placed in perforated trays are “flash” sterilized for 3 minutes at 270 E F (132 E C). Sterilization timing begins when the above temperature is reached, not before. Dry-Heat Sterilization.—The use of dry heat as a sterilizing agent has limitations. It should be restricted to items that are unsuitable for exposure to moist heat. High temperatures and extended time periods are required when using dry heat. In most instances, this method often proves impractical. The temperature must be 320EF (160EC), and the time period must be at least 2 hours. CHEMICAL STERILIZATION.—Only one liquid chemical, if properly used, is capable of rendering an item sterile. That chemical is glutaraldehyde. The item to be sterilized must be totally submerged in the glutaraldehyde solution for 10 hours. Before immersion, the item must be thoroughly cleansed and rinsed with sterile water or sterile normal saline. It should be noted that this chemical is extremely caustic to skin, mucous membranes, and other tissues. The most effective method of gas chemical sterilization presently available is the use of ethylene oxide (ETO) gas. ETO gas sterilization should be used only for material and supplies that will not withstand sterilization by steam under pressure. Never gas-sterilize any item that can be steam-sterilized. The concentration of the gas and the temperature and humidity inside the sterilizer are vital factors that affect the gas-sterilization process. ETO gas-sterilization periods range from 3 to 7 hours. All items gas-sterilized must be allowed an aeration (airing out) period. During this period, the ETO gas is expelled from the surface of the item. It is not practical here to present all exposure times, gas concentrations, and aeration times for various items to be gas-sterilized. When using an ETO gas-sterilizer, you must be extremely cautious and follow the manufacturer’s instructions carefully. Preparation of Supplies for Autoclaving Comply with the following guidelines in preparing supplies that are to be autoclaved.  Inspect all articles to be sterilized, making sure they are clean, in good condition, and in working order.  Wrap instruments and materials in double muslin wrappers or two layers of disposable sterilization wrappers.  When muslin wrappers are routinely used, launder them after each use, and carefully inspect them for holes and tears before use.  When articles are placed in glass or metal containers for autoclaving, place the lid of the container so the steam will penetrate the entire inside of the container.  Arrange the contents of a linen pack in such a way that the articles on top are used first.  Label every item that is packaged for sterilization to specify the contents and expiration date.  Do not place surgical knife blades or suture materials inside linen packs or on instrument trays before sterilization. 2-32