멸균기 내에 있는 모든 물품에는 공기가 들어 있으며 스팀을 확산시키는데 가장 큰 장애물은 바로 이공기다. 스팀이 공기와 혼합 되면 혼합된 부분 중 스팀만이 열전달 역할을 하므로 응축률이 낮아져서 효과적인 멸균이 어렵게 된다. 멸균기 챔버를 진공에 가깝게 공기를 배출 시켰다면 챔버의 모든 공간은 스팀으로 신속하게 채워질 것이며 멸균품인 섬유조직 내에 남아 있던 미량의 공기는 중력에 의해 챔버의 바닥에깔리게 될 것이다.
C. Air Removal Indicators
The air removal indicator is intended to be used by a health care provider in a standardized test pack, e.g., Bowie Dick Test Pack, to assess the ability of a prevacuum sterilizer to remove air and allow steam to penetrate into wrapped goods and porous loads. The test pack is usually positioned over the chamber drain in an otherwise empty chamber. An inefficient air removal stage, an air leak, or non-condensable gases in the steam supply are some of the conditions that could cause an incomplete change in the air removal indicator, e.g., uneven color change. The Bowie Dick Test is not an indication that the sterilizer has reached the parameters for sterilization.
G. Air Removal Indicators
For the air removal indicators, FDA recommends that you determine the following performance criteria and endpoint specifications inside the test pack (Bowie Dick Test).
You should provide pass/fail results demonstrating that the indicator does not reach its endpoint when exposed to dry heat at 140±2°C for 30 minutes.
You should also provide pass/fail results demonstrating the tolerances for the detection of air in a prevacuum sterilizer. You can simulate this fault condition by injecting air or by not pulling a complete vacuum to produce a non-uniform change in the indicator agent. You should include a thermocouple graph showing the decrease in temperature during the fault condition at the different points in the cycle.
For greater sensitivity in detecting air over a larger area, FDA recommends that air removal indicator sheet in the test pack should measure approximately 8 inches by 10 inches. The indicator agent should cover a large percentage of the test sheet and it should be uniform.
You should provide specification for the porosity of the material used to construct the air removal indicator. ANSI/AAMI ST 66 recommends using a standard densitometer to measure the time required for a given volume of air (25 ml to 300 ml) to flow through a standard area of the indicator being tested.
