Say the worker refuses that order and their boss says "okay, you're fired". Would we also give that worker legal protection? Would we also hold accountable the higher ups who gave that order and set the policies for how trains are to be run? If not, then you now understand why the accident happened.
Yes I believe that's exactly what is to happen. See this explicitly spelled out https://www.osha.gov/laws-regs/mou/2012-07-16 .
I've worked in goods transport in interstate navigable waterways and we had the same thing, literally anyone can "stop work" for unaddressed imminent dangerous conditions and are protected against retaliation. Even if the protection fails it is better my own family starve to death than to poison an entire city; just following orders isn't an excuse (and in any case, such a company of such character company would fire you after the wreck).
note: not legal advice
Note: this is not individualized advice and I am not a lawyer.