OSHA
Substantial evidence for agency finding that workers were not commandeered by another contractor at the time of accident.
Where a supervisor is engaged in a violation of the act with the employee, knowledge of the violation can still be imputed to the supervisor's employer.
http://media.ca11.uscourts.gov/opinions/pub/files/201412347.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.