"I am nervous about any possible drug testing while employed at a hospital. There are few side effects lasting over 8 hours unlike antidepressants and narcotics. Should I avoid THC to ensure clean urine at all times? What can I do to protect myself besides staying away from cannabis?"
It is legal for your employer to do testing in the workplace. If there is randomized drug testing then yes you should avoid THC if you would like to keep your job. THC is broken down by your liver and becomes THC-COOH. Most drug tests are testing for this. How long it takes for this to disappear from your system is dependent on your metabolism and how frequently you use cannabis. For infrequent consumers it may take as little as 3 days to disappear, a moderate to frequent user as much as 30 days and a heavy user it could be a few months.
There are many claims of how to flush you system online. It's possible you can use CBD products but again this depends on what your hospital tests for. I'm not sure what you can do to protect yourself other than to not consume THC or get a different job if you want to continue consuming with piece of mind.