The term Laminar Flow as it applies to hoods or clean air equipment can mean many things. “Laminar Flow” typically means air flowing in one direction (unidirectional) with very low turbulence. In a horizontal “Clean Bench” air flows straight out of the hood towards the operator. In a true Vertical Flow clean bench the air flows directly down onto the worksurface, then out into the room. Some people will call Class II Biological Safety Cabinets (BSCs) “Vertical Flow” cabinets although that is technically incorrect.
The most common reference standard for clean air devices is the Institute of Environmental Sciences and Technology (IEST) Recommended Practice, IEST-RP-CC-002.4 for “Unidirectional-Flow, Clean-Air Devices”.
The Institute of Environmental Sciences and Technology Recommended Practice, IEST-RP-CC-002.4 for “Unidirectional-Flow, Clean-Air Devices” defines laminar flow equipment as: clean benches; clean work stations; wall and ceiling-hung modules; and other laminar flow clean air devices with self-contained motor-blowers.
Like Biological Safety Cabinets, most manufacturers recommend annual testing and certification. Different types of users may need to meet industry or regulatory certification requirements. The Joint Council of Accredited Hospital Organizations (JCAHO) recommends certifications at least annually in health care organizations. USP 797 requires Compounding Pharmacy’s to be certified semi-annually. IEST-RP-CC-002.4 recommends testing at “regular periodic intervals, at a frequency consistent with location, function, and established guidelines”, and “following potentially disruptive events, such as relocation of the device or replacement of the HEPA/ULPA filters”.
IEST-RP-CC-002.4 recommends the following tests for certification in the field: Air Flow Velocity; HEPA/ULPA Filter Installation Leak Test; Induction Leak Test/Backstreaming Test (when appropriate); Lighting Level (when appropriate); Noise Level (when appropriate); Vibration (when appropriate). The “when appropriate” clauses recognize the necessary testing differences between a horizontal flow clean air bench and a ceiling-hung laminar flow module that is 8 feet off the floor.
Laminar Flow units can be affected by the same problems as biological safety cabinets, i.e., incorrect location in the work room, in proximity to high traffic areas or doors, room ventilation problems, or building electrical limitations.