The problem with a major problem like a train wreck/poison gas spill is the major screwups that happen right afterward. IMHO, waiting to be told to get the hell out doesn't make much sense.

I was living in Las Vegas, NV, when the Pioneer Chlor Alkali facility in nearby Henderson started leaking from a faulty valve.

The employees thought they could control it, so they didn't call for help.

A passing motorist smelled the gas & saw the green cloud, called 911 & got laughed at by the dispatchers because what could that dumb broad know?

Someone else called 911 a little later, so someone was finally bright enough to figure out that there might be a problem.

Half an hour after the first call, the first alarm went out.

When the first firefighters arrived, still no alarm had been activated, & the employees had been overcome by the gas.

The protective clothing & SCBA units had been stored at the contaminated facility instead of someplace nearby where they could be reached & used.

Communications weren't set up to work between the different responding parties (shades of 9-11), as usual.

Over a period of several hours, 70 tons of chlorine gas escaped. Nearly 7,000 people were evacuated from the area (quite heavily residential -- good place for a chlorine factory), & about 200 were taken to hospitals.

The only group that was able to shelter in place was a nearby hospital, where they decided to set the air conditioning to recirculate only the interior air, as evacuating the patients would expose them to the gas.

IMHO, if there's a freight train derailment, just get the hell out. By the time the people "in control" figure out what's going on, you & your family might well be dead. Grab 'em & git! If nothing happens, call it a fire drill.

Sue