When it comes to domestic hot water recirculation design, OSHA safety provisions and ASHRAE 90.1 energy efficiency requirements have put plumbing engineers between the proverbial rock and hard place. In an effort to minimize the energy penalty associated with mandatory domestic hot water recirculation, ASHRAE 90.1 has created operational parameters for these systems. The problem is that these parameters are in direct conflict with OSHA’s requirements for Legionella prevention.