There had been so many retrofits and extensions added to the ventilation system at Nemours Children’s Clinic in Jacksonville, Florida that engineers weren’t sure where their airflow problems were coming from. What they did know was that negative pressure and inadequate ventilation throughout the 30+-year-old building could support the spread of nosocomial infections. Their first steps in taking control of the situation was to seal the leaks in the exhaust shafts located on each floor and then seal the main shaft running down the length of the 11-story building.