Classification of Sterility Test Isolators

Sterility tests check for the presence of contaminants.

Sterility tests use one of a number of isolator types to ensure sterile products are indeed sterile. They check for the presence of viable microorganisms in the sample under examination.

Soft-Wall Envelopes

Soft-wall envelopes are made with flexible plastic. This plastic creates a container for the sample, just as an envelope does for a letter, to isolate it from the outside environment while its sterility is being tested. The flexible plastic used in soft-walled envelopes is relatively inexpensive.

Hard-Wall Envelopes

Hard-walled envelopes work in a similar fashion to soft-walled envelopes, but use rigid plastic instead of flexible plastic. Hard-walled envelopes are more expensive than soft-walled envelopes, but are used to protect testing personnel from substances that could be toxic or slightly radioactive.

Pressure

Isolators are also classified by the air pressure used in the testing process. Usually, isolators are kept at a positive air pressure, where the pressure within the isolator is greater than the pressure outside the isolator. This helps to keep contaminants out of the environment. When the substance being tested could be toxic or radioactive, the isolator's air pressure is kept negative: the air pressure inside the isolator is lower than the air pressure outside the isolator.

References

• "Validation of Sterility Test Isolators"; Daragh D. Byrne
• "Sterility Testing: Beware of the Pitfalls"; Martin Spalding, Jr.
• "The Physical Environment: Air Pressure"