What “deadly” errors have occurred so far?
Trains would run on time (which was the original reason the Standard Time Zones were established in the first place).
The various astronomers and even watchmakers were very keen on their ability of determine the exact moment of noon, the point of zenith of the sun, by “shooting the sun”. Trouble is, the astronomical definition of “noon” could vary only a few miles east or west of the point of observation. So it is obvious that trains that set fort at one time, would be far wrong on time only a few miles down the track, and the further the train traveled, the greater the error. Greenwich Mean Time IS included in the routing of aircraft across the world.
Also in a lot of electronic transmissions.
Daylight Saving Time probably has not yet cause “deadly” errors but it sure causes a lot of deaths: trafic accidents rate surges at each change that shortens sleep time by 1 hour.
My old parents always have horrible time coping with it, it’s a misery for them for weeks, twice a year. Just for it, I hate my guts DST, one of the stupidest idea invented by bureaucrats and the Malthusian peak-oil ideologues. It’s as if the unique and real purpose is sadistic: to butthurt people.
But DST is not the same thing as timezone, which is useful.