There is an article in the Houston Chronicle: Explosions reported at flooded Crosby chemical plant.
Company representatives and public officials are being very vague about the hazards.
Quote:
Authorities cautioned nearby residents to stay inside, turn off their air conditioning and close their windows and doors.
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Yet, they didn't clarify the extent of adverse health effects on residents who breathe in the fumes. Harris County Sheriff Ed Gonzalez likened it to a burning campfire. Moments later, Assistant Chief Bob Royall with the Harris County Fire Marshall referenced Gonzalez's comparison, then backtracked and did not confirm that the smoke was as harmless as a campfire. Instead, he called it "smoke, with carbon particles in it." "You don't want to stand in smoke, do you?" Royall said. Rennard called the health effects relative. "They're noxious, certainly," Rennard said. "If you breathe in the smoke, it's going to irritate your lungs."

Another article in WaPo: Chemicals ignite at flooded plant in Texas as Harvey’s devastation lingers.
WaPo article has a bit more detail on the potential danger.
Quote:
A variety of federal agencies have warned about the dangers of organic peroxides the Crosby plant produces. The Occupational Safety and Health Administration warns that “contact of organic peroxides with the eyes should be avoided. Some organic peroxides will cause serious injury to the cornea, even after brief contact, or will be corrosive to the skin.”  It added that “many organic peroxides also burn vigorously.” An earlier study done for the EPA found that organic peroxides are skin and eye irritants and could also cause liver damage.

Last night on MSNBC Rachel Maddow said that Texas law was changed in 2015, since then the company does not have to publicly release either it's safety plan or any details about what is actually on site at the plant. The company claims that they planned for a worst case scenario, but was overwhelmed by Harvey. However, one of her guests said that there was a way that the company could have mixed in another chemical which would deactivate the organic peroxides so they wouldn't explode, but that would have meant losing some feedstock. The guest also said that keeping a supply of those deactivating chemicals on site is SOP at some plants.

As is often the case in these situations, it is hard to know who or what to believe.
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"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz