The long-accepted ventilation guideline of 10-15 room air changes per hour is based on the observation that this figure provides sufficient ventilation to keep odors below objectionable levels. Heating, ventilation and air conditioning (HVAC) systems in animal facilities require constant monitoring to assure proper ventilation and appropriate temperature and humidity levels. DLAM is responsible for maintaining these conditions, and any departures from appropriate levels should be reported to the DLAM office immediately. Facility problems noted after working hours should be reported to the veterinarian on call. Vivaria personnel work with the Department of Facilities Management to ensure that environmental control systems in animal facilities are functioning properly.