OSHA currently has two standards in which the PEL is adjusted based on the length of the work shift, both of which are lead standards:

29 CFR 1910.1025
29 CFR 1926.62

All other PELs are based upon 8-hour time weighted average (TWA), a short term exposure limit (STEL), or a ceiling limit (C).

The lead PEL of 50 micrograms per [...]