The air curtain generated by the linear slot diffusers serves as a barrier of clean air between the surgical zone and the "old" air in the room perimeter. This prevents contamination by any particulates which may be recirculating in the room, particularly near the ceiling level where laminar diffusers are most likely to entrain room air, and carries them down and away from the surgical zone toward the low-level exhaust grilles.
The air curtain should be sized to deliver between 25 and 45 cfm/ft:
ASHRAE 170 specifies the laminar flow diffuser requirements inside the air curtain as 70% coverage of the area defined by the operating table, plus a 12" offset in every direction. Discharge velocity is specified at between 25 and 35 cfm/ft2.
For more information, please consult the Price Engineer's Handbook.