The following techniques can improve your success with online searching, whether you're searching a catalog for books or a database for articles:
Use these resources to explore working populations (i.e. "construction workers", "retail workers", "truck drivers, etc.) and the occupational health issues they encounter.
Where to find it?
Professional Organization Websites (Does your working group have a professional organization? A union? Do they have anything to say about work-related injuries? A policy paper, newsletter article, fact sheet, training manual, etc. can be considered grey literature.)
Government Websites (Almost everything from the government is grey literature! Think about resources from the CDC/NIOSH, DOL, laws, data from the Census, etc.)
It's always a good idea to run your grey literature resource by your professor.