PHSS Clarity In GMP Guidance – Cleanroom Airflow Definitions

PHSS Clarity in GMP Guidance Note- Cleanroom Airflow Definitions: Aligning Ui-Directional Airflow (UDAF), Localised Uni Directional airflow (L-UDAF) and Grade A Air Supply

Uni-directional airflow (UDAF) where airflow vectors move in the same direction from a HEPA filtered source is one of the main environmental airborne contamination control attributes in pharmaceutical manufacturing (together with pressure differentials between clean areas). UDAF in Pharmaceutical applications is sometimes referred to as LAF (Laminar airflow) where scientifically airflow vectors would be straight and parallel.

Introduction
Uni-directional airflow (UDAF) where airflow vectors move in the same direction from a HEPA filtered source is one of the main environmental airborne contamination control attributes in pharmaceutical manufacturing (together with pressure differentials between clean areas).
UDAF in Pharmaceutical applications is sometimes referred to as LAF (Laminar airflow) where scientifically airflow vectors would be straight and parallel. Although straight and parallel airflow vectors are generated from the HEPA filtered source because air extract or exhaust points are typically at low level on the side or junction with floor of the clean air zone airflow vectors no longer continue to be straight and parallel (LAF) as they track towards exit points.In changing direction towards the exit air points the vectors should continue to follow a single (uni) -directional path without adverse turbulence or reverse change of direction where air flow re-enters the source air from the HEPA filter referred to as ‘First air’.

First air principles apply in air flow protection during aseptic processing interventions where complementary good aseptic technique is required where no potential particle or contamination generating source should be between the HEPA filter sources where clean air is first delivered to the process point that is required to be protected by clean airflow. UDAF is also applied to reduce the particle concentration by replacement or dilution with clean air to maintained specified conditions of particle cleanliness. In a Grade A zone UDAF is expected to cover the complete zone (unless specified to be turbulent flow) with continuous particle monitoring and down-flow velocity monitoring applied in process monitoring. Airflow visualization is a key of protective airflow pattern qualification e.g. CFD; computational fluid dynamics, Smoke studies and LR Method airborne particle transfer challenge.

In some applications of airflow protection within a Uni-directional airflow (UDAF) zone or at an interface with process equipment e.g. autoclave moist heat sterilizer offload a more localized airflow protection is required with a higher airborne classification than the complete zone it is included. The localized airflow protection is defined as Localized –Unidirectional airflow: L-UDAF.

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