Risk for contamination in a cleanroom with weakened aerodynamic barrier

The risk for contamination in a pharmaceutical cleanroom was investigated through tracer gas measurements in 13 different scenarios, when the aerodynamic barrier between an airlock (AL) and a cleanroom (CR) was weakened by opening the door separating the rooms. Air velocities through the doorway, differential temperature between the airlock and the cleanroom, different door opening speeds and different walking paces of a mannequin entering the cleanroom were the four parameters in focus. The study was conducted in a full-scale cleanroom mock-up (4.7 x 3.5 x 2.5 m), where each scenario was repeated three times. The results of the investigation show that air velocity through the doorway is the most important design parameter to ensure the aerodynamic barrier, when an average air velocity between 0.14 m/s (resulted in 209 l of migrated air) and 0.33 m/s (resulted in 62 l of migrated air), which was achieved at isothermal conditions and with a door opening time of 10 seconds. Increasing the door opening time to 20 seconds diminishes the effect of a higher air velocity to neglectable levels. Last by not least, the differential temperature between airlock and cleanroom has an impact on the air migration, where a warm cleanroom (24 °C) and a cold airlock (20 °C) showed a low contamination risk with a door opening time of 10 seconds. A warm cleanroom (24 °C) and a cold airlock (20 °C) showed on the other hand a high level of air migration with almost 1.500 l of contaminated air entering the clean zone with a door opening of time 10 seconds. (paper)