That's when, according to the complaint, BP took a hydrogen compressor in the Ultracracker unit offline.
The compressor traps noxious chemicals. Instead of shutting down the entire unit while the compressor was out of commission, BP opted to send those gases to a flare to be burned off.
The lawsuit says that decision resulted in the release of more than half-a-million pounds of chemicals and compounds, including 17,000 pounds of benzene, a known carcinogen.
The lawsuit, filed on behalf of more than 2,200 people who work at or live near the refinery, is asking for 10 billion dollars in punitive damages.
A spokesperson with BP in Houston declined to comment on the lawsuit, saying it's company policy not to talk about pending litigation.