Know how air passes through the cabinet. HEPA-filtered air protects personnel. Proper airflow is measured annually (or more frequently) by a certifier measuring air speed, after which a stamp of approval is placed on the cabinet.
Work at the proper sash height. A window sash that is not at the certified working level may compromise the balance of airflow. Inflow velocity that is too strong risks allowing contaminated air into the sterile work area. Downflow velocity that is too strong may push cabinet air out into the lab without filtering, or create turbulence, which increases contamination risk.
Do not cover the air-intake grill (including blocking it with elbows and arms). Blocking the grill can cause lab air to enter the work zone or work-zone air to enter the lab.
Keep movements to a minimum. Rapid, sweeping arm movements can disrupt the air curtain. To reduce risk, arms should be moved in and out and perpendicular to the face opening of the cabinet. Even movement of personnel in the room can alter performance, for instance, quick opening and closing of doors and walking briskly past the hood face.
Minimize splatter. Many common procedures can cause splatter or aerosolize chemicals. Class II cabinets are designed so that horizontally nebulized spores will be captured by the downward-flowing cabinet air within 14 inches of travel. As a general rule, keeping clean materials at least 12 inches away from aerosol-generating activities will minimize the potential for cross-contamination.
Utilize your work area effectively. It is recommended to use the middle-third of the work area. All operations should be performed at least four inches from the front grill. Materials or equipment placed inside the cabinet may disrupt airflow; the resulting turbulence can lead to cross-contamination or even breach of containment.
Work from “clean to dirty.” Activity should proceed from “clean to contaminated” areas across the work surface. Materials and supplies should be placed in such a way as to limit the movement of dirty items over clean ones. To prevent airflow imbalance within the work zone, maintain a balance of materials and supplies from left to right. Bulky items should be placed to one side of the interior. All materials should be placed as far back as possible. Aerosol-generating equipment, such as mixers and centrifuges, should be at the rear to take advantage of the air split.
Handle containers properly. Do not hold open tubes or bottles in a vertical position and cap them as soon as possible. Caps should not be placed on toweling.
Hold Petri dishes and tissue culture plates correctly. When working with plates and Petri dishes, hold the cap over the dish to minimize the impact of downward-flowing air.
Use care with suction flasks and aspirator bottles. Aspirators or suction flasks should be connected to an overflow collection flask containing appropriate disinfectant and to an inline HEPA or equivalent filter. This will protect personnel who service the equipment. Inactivation of aspirated materials can be done by placing sufficient chemical decontamination solution into the flask to kill microorganisms as they are collected. Once inactivation occurs, liquid materials can be disposed of appropriately as noninfectious waste.
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