OSHA Chemical Database with PELs, CAS#, PPE, chemical properties,  and much more.

OSHA PDF - Preventing Mold-Related Problems in the Indoor Workspace

OSHA Technical Manual (OTM)
Section II: Chapter 1 for personal air sampling.

OSHA page on chemical hazards and toxic substances in the workplace.

OSHA booklet -  Indoor Air Quality in Commercial and Institutional Buildings

Link to 29 CFR 1910.1200 OSHA Hazard Communication Standard