You can find treatises on Occupational Safety and Health Law on Westlaw, Bloomberg, and Lexis. Do not be confused that two different treatises have the same name.
Occupational Safety and Health Law, 4th ed., Mark A. Rothstein, editor. (Last updated April 2020).
Occupational Health and Safety Law, 4th ed., Gregory N. Dale & P. Matthew Tracey, editors. (Last updated 2018).
N. Peter Lareau, Labor and Employment Law, Part VII (last updated 2021).
Arthur Larson and Lex K. Larson, Larson's Workers' Compensation Law, (last updated 2017).
CCH, a division of the publisher Wolters Kluwer, produces several resources that you may encounter in a career in OSHA law. Two of their most important titles are employment Safety and Health Guide, and Occupational Safety and Health Decisions.