We are not medical doctors and do not diagnose illness. We are, however, highly-trained indoor environmental experts who understand the health effects of environmental exposure and can identify indoor environmental issues that are likely to be affecting an individual in undesirable ways. This often means performing a basic indoor air quality assessment to determine if there are any markers that appear in the test results. We think of this as reading the 'vital signs' of a building: collecting airborne particulate counts, obtaining levels of CO and CO2 and common offensive chemicals, looking for signs of known toxins often found in homes, and scanning building materials for moisture using thermal imaging devices are just some of the techniques used by ESG investigators to assess a building. Once the investigator has gathered some forensic data, additional sampling of air and surfaces inside the building may be necessary to rule out certain common offenders such as indoor allergens. We call this service a Health Hazard Evaluation, and the format closely resembles that of NIOSH when it conducts an assessment of a school or commercial building.