Sodium hydroxide tanker explodes in Ohio

A tanker carrying sodium hydroxide exploded at the Royal Chemical plant Wednesday morning in Macedonia resulting in three reported injuries, according to Macedonia Fire Chief Brian Ripley.

Two of the three people injured were transported to Metro General Hospital in Cleveland, one of them with life-threatening burns and the other with non-life-threatening, but critical burns, Ripley said.

The third individual was evaluated on the scene.

Investigators are still unsure what caused the explosion, which Ripley said occurred around 11:40 a.m. He said when crews arrived, the tanker had been split in two due to the explosion with half of the tanker inside of the building and the other half outside of the building...

I'm genuinely surprised this happened, i.e. how does sodium hydroxide cause anything to explode? I predict two things - either the tanker was over-pressured (i.e. the loader decided to pump it in without a vent) and ruptured, or the tanker had water in it and sodium hydroxide fluid was pumped in and it got hot, boiled and then ruptured. Kind of strange.