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2011). With respect to indoor air contaminants for which inhalation is the primary route of <br />exposure, the critical design and construction parameters are the provision of adequate <br />ventilation and the reduction of indoor sources of the contaminants <br />Indoor Formaldehyde Concentrations Impact. In the California New Home Study <br />(CNHS) of 108 new homes in California (Offermann, 2009), 25 air contaminants were <br />measured, and formaldehyde was identified as the indoor air contaminant with the highest <br />cancer risk as determined by the California Proposition 65 Safe Harbor Levels (OEHHA, <br />2017a), No Significant Risk Levels (NSRL) for carcinogens. The NSRL is the daily intake <br />level calculated to result in one excess case of cancer in an exposed population of 100,000 <br />(i.e., ten in one million cancer risk) and for formaldehyde is 40 µg/day. The NSRL <br />concentration of formaldehyde that represents a daily dose of 40 µg is 2 µg/m3, assuming a <br />continuous 24-hour exposure, a total daily inhaled air volume of 20 m3, and 100% <br />absorption by the respiratory system. All of the CNHS homes exceeded this NSRL <br />concentration of 2 µg/m3. The median indoor formaldehyde concentration was 36 µg/m3, <br />and ranged from 4.8 to 136 µg/m3, which corresponds to a median exceedance of the 2 <br />µg/m3 NSRL concentration of 18 and a range of 2.3 to 68. <br />Therefore, the cancer risk of a resident living in a California home with the median indoor <br />formaldehyde concentration of 36 µg/m3, is 180 per million as a result of formaldehyde <br />alone. The CEQA significance threshold for airborne cancer risk is 10 per million, as <br />established by the South Coast Air Quality Management District (SCAQMD, 2015). <br />Besides being a human carcinogen, formaldehyde is also a potent eye and respiratory <br />irritant. In the CNHS, many homes exceeded the non -cancer reference exposure levels <br />(RELs) prescribed by California Office of Environmental Health Hazard Assessment <br />(OEHHA, 2017b). The percentage of homes exceeding the RELs ranged from 98% for the <br />Chronic REL of 9 µg/m3 to 28% for the Acute REL of 55 µg/m3. <br />The primary source of formaldehyde indoors is composite wood products manufactured <br />with urea -formaldehyde resins, such as plywood, medium density fiberboard, and <br />796117 <br />