When I was an environmental, health and safety consultant, I worked for several firms and then did my own gig for a few years. One of my old clients, another E,H&S consulting firm has their Certified Industrial Hygienist out on maternity leave and turned to me to help them out as another CIH. I've been helping them out in the evenings and on weekends to design sampling programs, direct their staff on doing the actual work during the work week, I write/review reports, etc. Its sort of nice, exercising my brain a bit in ways that I haven't had to in a decade. $100/hr for me, they bill me out at $210/hr. I get no benefits, but I'm under their general liability and E&O insurance as a part-time employee. Made enough this month to buy a new Rolex Submariner, not that I need another one. But nice side money.