Duct leakage affects the accuracy and performance of a laboratory's room pressurization. When designing a laboratory pressurization system, an engineer needs to consider the impact of duct leakage on room pressure control. Air leaking into or out of ductwork between a flow measurement device and a laboratory envelope can result in a significant pressure-control error. Labs that house radioactive or biological hazards are required to maintain a negative pressure to contain these hazards; standards vary according to the local authorities. Ducts for these conditions are usually welded, so the leakage rate is virtually zero. Cleanrooms, on the other hand, are normally operated at a positive static pressure to prevent infiltration of particulates so the leakage rate is less critical. Nonetheless, cleanroom ductwork is also typically welded.
