Laboratory air quality and room ventilation rates

This report investigates the relationship between laboratory air quality and room air change per hour (ACH) rates under controlled releases of organic solvent during simulated routine bench-top work as well as small spills. The accumulation, peak concentration, and clearance of airborne contaminants was found to be proportional to the overall room ACH rate, and significantly influenced by chemical vapor pressure and density, room temperature, and the direction and velocity of room air currents. This work reinforces the concept that no single ACH rate is appropriate for all rooms, contaminants, or operations. It also reminds practitioners that ACH rates cannot simply be lowered below original design specifications without consideration of the engineering and safety implications of the change. Of the ACH rates evaluated, the greatest relative improvement in chemical concentration and clearance time from the room, whether under spill or continuous bench-top release conditions, occurred between 6 and 8 ACH, with diminishing returns for rates greater than 12 ACH. This suggests that ACH rates above 12 are generally unnecessary while those below about 8 warrant careful consideration, with lower levels suitable only for low hazard operations and during periods of inactive non-occupancy. Re-engineering of supply and exhaust air diffusers to provide optimal location, number, and style can be an effective means to functionally increase the efficiency of laboratory ventilation systems and potentially allow for designs at lower ACH rates.