There’s a long history of this. That’s not important because it makes this event better in any way, but it is important know that it will happen again–the very next time there is a major leak, be it chemical or radioactive,
Corporate and government responses get determined by a set of PR principles and practices that the actors call “damage control.” But what they call “damage” is almost entirely the spread of information,. particularly the spread of information in the early stages of publicity, when a substantial percentage of the population may take an interest. Because of this, respondents and residents near impacted areas should be aware of a few things in advance and act accordingly, despite corporate and government announcements.
Responsible parties will act to minimize their culpability in court or by reduced sales or whatever. They will therefore exaggerate descriptions of response and control and deny danger wherever they can. The standard for this is consistent: it is personal and corporate deniability within the period of extensive media attention.
To be as clear and blunt as possible, authorities will say things are fine or that danger is not certain as long as they feel that they can later deny in court that they knew differently.
This plays out differently case by case. We now know, for example, that the government knowingly killed many thousands of Americans by testing nuclear warheads in the Western US. The poisoning was particularly extensive and cruel because people had very little knowledge of radiation poisoning, so that it was easy to imagine that there would be little or no retribution. Media coverage of the leaks at Three Mile Island by Harrisburg, Pennsylvania were not particularly honest and left out the very telltale pattern of leukema and cancers downwind and downstream of the site in years following the major leaks. But they did not deny danger to the same extreme extent because the population was sufficiently informed that possibilities of a class action lawsuit were a real concern.
These principles operate similarly with fracking accidents and gas leaks (Aliso Canyon, CA 10/15), oil leaks (BP, Exxon-Valdez), and leaks of very toxic chemicals (Bhopal).
Once the leak happens, there are a lot of motives to get far away.