Via the Houston Chronicle, this news:
A shelter-in-place for the city of Deer Park that stemmed from a release of hydrogen sulfide was lifted late Tuesday, authorities said.
About 6:50 p.m., the Deer Park Police Department posted on social media that the city was monitoring a Level 3 incident at Lubrizol Deer Park, a facility that manufactures specialty chemicals and additives. According to the company's website, its plant in Deer Park is the "the world's largest additives plant." A shelter-in-place was subsequently implemented for the city.
By 10 p.m., Deer Park authorities said Lubrizol had de-escalated the incident to Level 2 after confirming the released chemical was generated when phosphorus pentasulfide came into contact with water.
It's relatively rare there is pretty specific data about what chemical was released and why. A phosphorus pentasulfide/water reaction would do it!