The NIOSH Recommended Exposure Limit (REL) for lead is a Time Weighted Average of 50 micrograms per cubic meter of air (µg/m3) over 8-hours.
The required (OSHA) Permissible Exposure Limit (PEL) for lead is also no greater than 50 µg/m3 averaged over an 8-hour period. The PEL is reduced for shifts longer than 8 hours by the equation PEL = 400/hours worked.
The required (OSHA) Permissible Exposure Limit (PEL) action level for lead in general industry and the construction industry is a Time Weighted Average of 30 µg/m3 over 8-hours.
1 NIOSH Adult Blood Lead Epidemiology and Surveillance (ABLES) https://www.cdc.gov/niosh/topics/ABLES/description.html
2 Council of State and Territorial Epidemiologists (CSTE) 2009 Position statement: Public health reporting national notification for elevated blood lead levels [ http://c.ymcdn.com/sites/www.cste.org/resource/resmgr/PS/09-OH-02.pdfpdf iconexternal icon (PDF 99 KB, 11 pages)]