Here's a few easy, basic safety fixes we offer to our commercial janitorial customers at no extra charge; you might want to consider working into your safety program any you've not addressed already:
1) Check the battery on the lighted EXIT sign over your front door. The battery should last for years; it's there to provide power to the light if the building power is off. And, if the building power is off, that's when you want to have a lighted EXIT sign.
2) Check exterior security lighting. Perhaps this is best done by the janitor, given that he is there after dark, which is when you can best see where you need security lighting.
3) Check the janitor closet for unlabeled bottles, like the window cleaner that your janitor uses. Technically, that squirt bottle is, per OSHA, an "unlabeled chemical container", subject to a fine. You might also look for, and properly dispose of, any outdated, or leaking, or uncorked bottles. Get rid of clutter, and that case of paper towels sitting on the water heater. Also, be sure that you have Material Safety Data Sheets on any and all chemicals in the facility, located so that your employees can find them easily. The OSHA regs, and fines, are there to "encourage" you to protect the safety of your people - it's considered a good idea to have the manufacturer's safety info on hand if you have to run somebody to the emergency room, because he mistook the window cleaner for sarsaparilla. That's why the fine goes to you, not the janitor service that left you the offending bottle.
4) Check your fire extinguishers. Most folks are aware that the extinguishers must be on site, within a prescribed distance from any employee work station, and that they need be inspected, and recharged if necessary, annually by a trained technician. Many are not aware that they must also be given a simple visual inspection monthly: you confirm that the extinguisher is in its proper place, that the little arrow is in the green field, that the lock-out ring is in place, and that no ugly chemical is oozing out of the crack in the bottom. Then, to verify, you date and initial the card that the tech put on at the last annual inspection. Simple (if you remember to do it), and probably a good idea that, if you are going to have yourself a fire extinguisher, you once in a while make sure that it is working. I really hate it when I try to put out a fire in the office, and the fire extinguisher doesn't work.
We do the above, for those clients who have requested us to take it over, during our regular monthly customer service inspection of the facility (except for the exterior safety lighting check - we monitor that nightly). Perhaps your janitor might as well?