This is typical of the profit minded fast growth mentality [chap chap] espoused by that cabal in Beijing. Certainly, any objective person has to question the role that corruption [and cutting corners] plays in EIA processes in places like Tianjin and in China as a whole.
For example, where is the wisdom of building a storage facility or warehouse for hazardous materials so close to a residential area? Well, I guess, only in China. In the U.S. community groups -- those "pesky" civil society folks -- would be up in arms quoting zoning ordinance a, b, and c, and would ensure its demise.
I can't count the number of times when in Seoul or across the Sea of Japan, I find myself breathing polluted air PM2.5 courtesy of the maendeleo chap chap Chinese.
I highly doubt it; China is actually a very tough place for any would-be terrorist.
My guess: an industrial mishap. In many places in China, the drive to minimize production costs, make money (for owners of factories), and keep China as the "world's manufacturer" (for the government) mean that corners are being cut all over the place. There are not-too-infrequent "small disasters", with many more waiting to happen. The government knows this, but generally finds it "helpful" to look aside.