1. CFR (Code of Federal Regulations). (2022a). Exposure limits for airborne contaminants [CFR Title 30, Chapter I, Subchapter K, Part 56, Subpart D, 56.5001]. U.S. Government Printing Office. https://www.ecfr.gov/current/title-30/chapter-I/subchapter-K/part-56
2. CFR (Code of Federal Regulations). (2022b). Exposure limits for airborne contaminants [CFR Title 30, Chapter I, Subchapter K, Part 57, Subpart D, 57.5001]. U.S. Government Printing Office. https://www.ecfr.gov/current/title-30/chapter-I/subchapter-K/part-57