Secondary Containment is a must when Designing a Contamination Control System

By Hank Rahe

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The margin for error in selecting and implementing contamination control solutions that provide adequate levels of protection is getting smaller and smaller.

Exposure limits for hazardous drugs continue to range at lower and lower levels as each new compound is introduced. Compounds with nanogram exposure limits are currently being discussed in the same manner as those with microgram limits were discussed in the '90s.

Controlling airborne exposures at the nanogram level requires two critical elements: validated engineering controls and documented testing of the systems to verify the containment capability of the engineering control. The attention to detail and understanding the capabilities of the engineering solution leaves no room for amateurs.

All containment systems have the potential to fail. Failure of even the most advanced system is going to occur, making it important to understand the probability and the implication of the failure. Failing safe is the key to a well-engineered contamination control system.

Systems that offer a single level of protection can place workers at risk because when the failure occurs there is no secondary protection in place. An example is the transfer of a hazardous drug from one container to another where a connection is required for the transfer. If the connection fails, then the hazardous drug will escape.

A better solution is to have secondary containment in place that will offer protection until the problem can be corrected. Glove bags are being utilized for secondary containment during transfers because of their flexibility and reasonable cost.

Barrier isolators offer protection for the operator and the product. The integrity of the structure of the enclosure and the pressurization scheme used with the air handling system gives a two-level system of protection.

How do we know the systems work as well as the resulting effect of the failure?

Testing is the only way to determine the containment capability of the system and the impact when the system fails. Ideally, testing would involve putting the contamination control system through every possible scenario using all the potential products the system could process.

This level of testing, in most cases, is not practical because of time, cost and the rapid introduction of new products. Because of these limitations, surrogate testing with well-designed tests have become the common means for verification of containment levels of the engineering controls.

Surrogate testing selects a placebo material with validated analytical methods that best represents the characteristics of the hazardous drug and uses the placebo as the test material. Design of the test is critical and should involve professional help with a background in design of experiments and sampling, as well as an understanding of industrial hygiene practices.

Things that are commonly missed without professional help are the number and location of samples required to verify consistent results; the need for replicate testing and an understanding of how the samples are to be collected. The most critical element is the interpretation of the results because without proper interpretation the testing amounts to nothing but raw numbers.

Tests results may not be valid because of the sampling techniques. What method best provides a reprehensive picture of the level of contamination? Is it air sampling, surface sampling or both? If surface sampling is used, what is the recovery rate of the collection technique and has it been validated?

Materials are recovered from surfaces at different rates depending on a number of factors so not all of the hazardous compound may be collected, leading to a false assumption that the containment solution provided a safe level of protection.

Containment systems require testing to verify capabilities. Testing is not a simple task and requires professionals to design the test and interpret the results.

Hank Rahe is director of technology for Containment Technologies Group and is a member of the CleanRooms Editorial Advisory Board. He can be contacted at [email protected].


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