Air Shower Design: Key Factors That Influence Cleaning Performance

What an Air Shower Is Intended to Do

An air shower is a self-contained chamber installed at the entrance to a cleanroom or controlled area. High-velocity filtered air is directed at personnel or materials passing through the chamber, dislodging surface particles from clothing, footwear and equipment. The dislodged particles are then captured by the return-air filtration system. The air shower does not sterilise; it reduces the particle burden carried into the cleanroom by personnel and materials.

Typical Operating Sequence

The person or trolley enters the air shower and the entry door closes and interlocks. The air shower cycle activates automatically, directing high-velocity air from nozzles positioned on the side walls and ceiling. The cycle runs for a defined period. At the end of the cycle, the exit door releases and the person proceeds into the cleanroom. The entry door cannot be opened until the exit door has been closed again, preventing simultaneous access from both sides.

Air Velocity and Nozzle Arrangement

The velocity of air at the nozzle outlet and the arrangement of nozzles across the chamber walls and ceiling are critical to cleaning effectiveness. Nozzles should be positioned to direct air at all surfaces of the person, including the back, sides and lower body. The number, diameter and spacing of nozzles, and the fan capacity required to achieve the specified velocity, are design parameters that must be confirmed for the specific chamber dimensions and application. Final air-velocity parameters depend on the approved design and project specification.

HEPA Filtration Considerations

The supply air in an air shower is filtered through HEPA filters before being directed at the person. The filter efficiency class must be appropriate for the cleanliness classification of the receiving cleanroom. Filter integrity testing should be carried out at commissioning and at intervals defined in the approved maintenance programme. The return-air path must also be filtered to prevent re-entrainment of dislodged particles.

Personnel Capacity

Air showers are available in single-person and multi-person configurations. The chamber dimensions must be sufficient to allow the person to rotate during the cycle so that all surfaces are exposed to the airflow. For facilities with high personnel throughput, the cycle time and chamber capacity must be matched to the shift-change schedule to avoid queuing at the cleanroom entrance, which can itself create a contamination risk.

Entry and Exit Door Interlocking

Interlocking prevents both doors from being open simultaneously. Electromechanical interlocks allow integration with access control systems, provide visual status indication and can generate door-open event logs for audit purposes. The interlock logic should also prevent the exit door from releasing until the full cycle has been completed, ensuring that the cleaning process is not bypassed.

Cycle-Time Considerations

The cycle time must be sufficient to achieve the required particle reduction. Shorter cycles reduce throughput delay but may not provide adequate cleaning. The approved cycle time should be established during commissioning and qualification, based on particle count measurements taken before and after the cycle. Cycle time should not be reduced without re-validation.

Construction and Internal Finish

Air shower chambers are typically constructed from stainless steel or powder-coated mild steel, depending on the application and cleaning requirements. Internal surfaces should be smooth and free of particle traps. Corners should be radiused. The floor should be non-slip and easy to clean. Viewing panels in the doors allow personnel to confirm the chamber is unoccupied before entering.

Emergency and Safety Provisions

An emergency release must allow the exit door to be opened manually in the event of a power failure or system fault. The chamber must not trap personnel. Emergency lighting and a clearly marked manual release are standard requirements. The interlock logic should fail-safe to allow egress in an emergency.

Installation and Maintenance Access

The fan, motor and HEPA filter housing must be accessible for maintenance without requiring entry into the cleanroom. Filter replacement should be possible from the non-clean side of the installation. The control panel should be positioned for easy access and should display cycle status, fault conditions and filter-pressure differential.

Air Shower versus Air Tunnel

An air tunnel is a longer version of an air shower, designed for trolleys, carts and larger equipment. The operating principle is the same, but the chamber dimensions, nozzle arrangement and fan capacity are configured for the larger cross-section. For facilities that transfer both personnel and materials, separate air showers and air tunnels may be required, or a combined unit with adjustable settings.

Information Required for Selection

To specify an air shower correctly, the project team should provide: the cleanliness classification of the receiving area; the number of personnel using the air shower per shift; whether the unit is for personnel, materials or both; the available floor space and ceiling height; the door configuration required (single-door, double-door, L-shaped or straight-through); the construction material and finish; the interlock and access control requirements; and the applicable qualification and documentation requirements.