For all whistleblower statutes enforced by OSHA, the investigative standard is whether there is reasonable cause to believe that a violation occurred. This standard applies to each element of a violation.
Under the reasonable cause standard, OSHA must believe, after evaluating all of the evidence gathered in the investigation from the respondent, the complainant, and other witnesses or sources, that a reasonable judge could rule in favor of the complainant. The threshold OSHA must meet to find reasonable cause that a complaint has merit requires evidence in support of each element of a violation and consideration of the evidence provided by both sides or otherwise gathered during the investigation, but does not generally require as much evidence as would be required at trial. Because OSHA makes its reasonable cause determination prior to a hearing, the reasonable cause standard is somewhat lower than the preponderance of the evidence standard that applies following a hearing. Accordingly, OSHA’s investigation must reach an objective conclusion – after consideration of the relevant law and facts – that a reasonable judge could believe a violation occurred.
View the manual in the link provided below.
https://www.osha.gov/OshDoc/Directive_pdf/CPL_02-03-007.pdf