Contamination Problems - in Laminar Flow Cabinets

Work performed in a laminar flow cabinet or a class II biological safety cabinet should be free of contamination because the air passing over the work is HEPA-filtered to remove microbiological contaminants. But occasionally contamination occurs and the cause must then be detected and eliminated. This technical bulletin aims to help in the detection and elimination of the cause of contamination and also as a guide to reduce the probability of such contamination ever occurring.

Following are the main reasons for contamination in a laminar flow cabinet or class II biological cabinet:

1. A problem with the cabinet.

A number of cabinet problems can reduce the effectiveness of the cabinet in preventing contamination. For example a leak in the HEPA filter will allow contamination of the product and a low airflow through the filter will reduce the air barrier to outside contamination.

Cabinets should be tested annually by an IANZ accredited test laboratory. If the cabinet complies with the standard, then it must be OK at the time of test. If the cabinet is moved or repaired or becomes suspect, it should be re-tested.

2. A problem with the cabinet’s environment.

AS 1386.7 recommends that the cabinet be located in a class 350 cleanroom. This is to provide relatively clean air to the cabinet and low background airflows in the room.

The HEPA filter is an efficiency device (usually 99.99% against viable particles), so if the supply air to the cabinet is uncontrolled, there may be some particles that penetrate the cabinet’s HEPA filter. However, it is very unlikely that bacteria would pass through a HEPA filter, even in an uncontrolled environment.

In practice, many cabinets are not located in cleanrooms and do work well in these less controlled environments. Nevertheless, a dusty room will compromise the performance of the cabinet and may lead to contamination problems. Also, air-conditioning systems can become contaminated and become microbial amplifiers if not regularly serviced. A test laboratory can measure the air quality in the room if a dusty room is suspected and/or perform airborne microbial counts.

It is very important that the cabinet is located away from doorways, passageways, air diffusers and the like which could lead to drafts at the face of the cabinet in excess of 0.25m/s. ( We recommend that cabinets be located at least 1 metre from these potential air disturbance sources.) A test laboratory can measure the airflow at the face of the cabinet under various conditions (e.g. when a person walks past the cabinet) and such testing may help to detect situations which may lead to contamination problems.

3. Poor Operator Technique.

We recommend the following:

• Essential operating instructions should be permanently attached to the cabinet. (Total Air Care offers a sticker with operating instructions at no charge to Test Laboratory clients.)
• Minimise equipment in the cabinet as excess equipment can interfere with cabinet airflow and cause turbulence..
• All cabinet operators should be trained in the principles of aseptic technique. (Total Air Care can provide on-site training including a brief power-point presentation and demonstration.)