It should be noted that OSHA when originally formed took all the chemical PEL-TWA limits from ACGIH to start the OSHA regulations. Of course as a government arm OSHA has been burdened with political influence and is basically hand tied with respect to industry. ACGIH is not a government arm and is made up of scientists, toxicologists, and medical physicians whose purpose is to protect people.
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIO
Quoting from OSHA:
"The U.S. Court of Appeals, Eleventh Circuit, vacated the 1989 Permissible Exposure Limits (PEL) listed in the "Final Rules" columns of Table Z-1-A of OSHA's Air Contaminants Standard, 29 CFR 1910.1000. Accordingly, no OSHA PEL exists for [substance]. However, in OSHA's opinion a potentially serious health hazard exists if employee exposures are not adequately controlled.OSHA therefore recommends that your employees exposures should be controlled to the more protective level of either the National Institute of Occupational Safety and Health (NIOSH) Recommended Exposure Levels (REL) of [level] or the American Conference of Government Industrial Hygienist(ACGIH) Threshold Limit Values (TLV) of [level]."