Terracon provided energy and indoor environmental consulting to assist in obtaining the U.S. Green Buildings Council (USGBC), Leadership in Energy and Environmental Design (LEED®) for Existing Buildings Operation and Maintenance (EBOM) certification for three commercial buildings in Tempe, Arizona. The project included two eight-story and one twelve-story commercial office buildings with multiple heating, ventilating, and air-conditioning (HVAC) systems. The client wished to obtain LEED EBOM Environmental Quality (EQ) Pre-requisite 1 (P1), Building Ventilation, and EQ Credit 1.1 (EQ 1.1), Indoor Air Quality (IAQ) Management Program. Terracon’s industrial hygiene group measured outdoor air flow rates for HVAC systems, and delivery of outdoor air to occupied spaces, to confirm compliance with ASHRAE Standard 62.1-2007, Ventilation for Acceptable Indoor Air Quality. A mass balance of CO2 was used to estimate the outdoor air fraction for 28 HVAC systems. Direct measurement of duct velocity using thermo-anemometer traverses and calculation of volumetric air flow was conducted for 15 systems. Minimum outdoor air delivery requirements for critical zones in occupied spaces were calculated using the ASHRAE 62MZCalc spreadsheet. LEED EBOM EQ 1.1 required inspection of building spaces to collect information about characteristics, finishes, and condition, HVAC system components, condition and hygiene, and operation parameters, and building pollutant sources and pathways. Data was collected and reported consistent with the U.S. Environmental Protection Agency (EPA) Indoor Air Quality Building Education and Assessment Model (I-BEAM) program.