Drug testing has nothing to do with safety just liability protection.

Drug testing is merely a function of risk abatement, specifically driven by the insurance industry. A company that has a testing program in place can get lower property and casualty insurance rates. Secondly there are some protections from civil and criminal cases offered by a testing program. A side benefit of a testing program is that it causes a self selection of sorts. People that routinely use drugs will not apply or want to work in an environment where they think they will get “outed’ there are exceptions and also a class of people that enjoy beating a system. So there is a net effect of a safer environment.