{"id":77807,"date":"2026-07-27T10:43:57","date_gmt":"2026-07-27T08:43:57","guid":{"rendered":"https:\/\/www.steelcobelimed.com\/?p=77807"},"modified":"2026-07-27T10:45:55","modified_gmt":"2026-07-27T08:45:55","slug":"medical-sterilizers-air-removal","status":"publish","type":"post","link":"https:\/\/www.steelcobelimed.com\/us\/medical-sterilizers-air-removal\/","title":{"rendered":"Medical Sterilizers: Air-Removal"},"content":{"rendered":"

Authored by Jonathan Carfora, Technical Services Trainer<\/em><\/p>\n

The most adverse element to proper steam sterilization is the presence of air (non-condensable gases) inside the chamber. Chamber air can cause cold spots and limit the ability of steam to penetrate the items being sterilized. Air shields the items being sterilized from the steam inside of the chamber, preventing surgical instruments from adequately receiving the full penetration they require, and sterility assurance cannot be complete. .<\/p>\n

A sterilizer program consists of three phases:<\/h4>\n
    \n
  1. Pre-treatment<\/li>\n
  2. Sterilizing<\/li>\n
  3. Post-treatment<\/li>\n<\/ol>\n

    While all three phases are critical for proper sterilization, the pre-treatment phase has the unique function of removing air from the sterilizer chamber. The process of removing air from the sterilizer chamber is known as conditioning.<\/p>\n

    Two methods are commonly used to condition (remove air) from the sterilizer chamber:<\/h4>\n
      \n
    1. Pre-vacuum (dynamic air aspiration)<\/li>\n
    2. Gravitational<\/li>\n<\/ol>\n

      Pre-vacuum (PreVac)<\/strong> conditioning methods use a vacuum pump to suck the air out of the sterilizer chamber. The vacuum pump runs until the chamber is allowed to reach a vacuum of less than 100 mbar absolute (1.45 psi absolute), this number may vary depending on the model and manufacturer of sterilizer. Steam is then admitted into the chamber. This process is repeated multiple times to ensure the chamber is free of air.<\/p>\n

      \"\"<\/p>\n

      Section \u20181\u2019 of the diagram shows the pre-treatment portion of the sterilizer cycle.<\/p>\n

      In this case, a PreVac conditioning step was performed. Notice how pressure alternatively drops and rises, forming a zig-zag pattern. This is the result of the vacuum pump running (pressure drop) followed by steam being admitted to the chamber (pressure rise).<\/p>\n

      \"\"<\/p>\n

      Pressure-time diagram Gravity<\/strong>
      \nSection \u20181\u2019 of the diagram shows the pre-treatment portion of the sterilizer cycle.<\/p>\n

      Steam is admitted into the chamber while the drain is opened. This causes pressure inside of the chamber to rise. While steam is being added to the chamber air is being forced out. Gravitational (gravity) conditioning is accomplished by introducing steam into the sterilizer chamber while the drain valve is open. Since steam is lighter than air, it displaces the air towards the drain using the force of gravity. The heavier cold air is pressed out of the sterilizer chamber drain by the steam being introduced.<\/p>\n

      The PreVac method is normally the preferred conditioning method because air is more effectively removed, and less steam is consumed. Gravity conditioning is usually reserved for items that are pressure sensitive and could be damaged by a strong vacuum.
      \nVarious tests such as the Bowie-Dick, dynamic air removal test may be used to check for proper conditioning. These tests usually consist of a test pack that simulates a difficult to sterilize load. A failed test indicates that the sterilizer is not effectively removing air or may have air leaks.<\/p>\n

      Reasons why conditioning could fail:<\/h4>\n