Containment Principles, Facility Design, and Engineering Controls
Containment has two arms: primary containment protects the worker and the immediate environment (biosafety cabinets, sealed centrifuge rotors, gloveboxes, HEPA-filtered exhaust), while secondary containment protects the outside environment (facility layout, airlocks, directional airflow, waste treatment, autoclaves). A candidate should be fluent in the four BSL tiers and what distinguishes them - BSL-1 needs handwashing and basic signage; BSL-2 adds restricted access, autoclave availability, and biosafety cabinets for aerosol-generating work; BSL-3 adds controlled access, directional inward airflow, self-closing doors, sealed penetrations, and HEPA filtration of exhaust; BSL-4 adds positive-pressure suits or class III cabinets and full waste/effluent decontamination.
Engineering controls are the highest-priority control because they act without relying on human behavior. Know the classes of biosafety cabinets: Class I (inward airflow, protects worker and environment, not product), Class II (recirculated/HEPA-filtered, protects worker, environment, and product - the workhorse), and Class III (gas-tight glovebox for maximum containment). Understand that a BSC is not a fume hood and vice versa, and that airflow directionality (clean-to-dirty) is the testable principle behind room pressurization.
Trap: assuming a BSC protects the product when only a Class II or III does; or assuming directional airflow alone substitutes for a cabinet.
Rule of thumb: if a procedure can create an aerosol, it belongs in a primary containment device regardless of the agent's risk group.