I based the “flammable gas in the cooling tower” idea on the reports of a very large report and house-shaking pressure wave out to a distance of miles from the site.
I don’t see how a turbine explosion could release that kind of pressure wave.
Even a flat-out boiler explosion would dissipate much of it’s energy against the walls of the plant.
But flammable gas inside the volume of one of those cooling towers could really release a hell of a pressure wave.
Be a cool thing to try, anyway. I mean, if anyone’s got a spare hyperbolic cooling tower laying around.
I've been inside those type natural draft water cooling towers. It is hard to imagine anything in there being the source of the explosion.
The hot water is sprayed in about 1/3 of the way up from the bottom. The spray continues down across a multitude of plates, dishes and other material designed to give the splashing water a convoluted path falling back to the bottom.
The splashing, spraying water warms the air, giving up heat from the water. The natural rising of the heated air draws in more air from the open bottom. The curving shape creates a speed up to the rising air drawing in air faster and giving more cooling.
In short, that is a big open concrete tube with a bunch of sprinklers in the bottom third. There is no containment vessel or sources of ignition inside it. There is one heck of a draft and an incredible amount of "fog".
That picture doesn't look like a stain to me, it looks like a place where water is seeping out from the inside spray.