The DuPont chemical plant can be seen from the Fred Hartman Bridge east of Houston.
Methyl mercaptan is a colorless gas mixed with natural gas, pesticides, jet fuel and plastics, according to the Agency for Toxic Substances and Disease Registry.
The gas is an irritant that can cause death by asphyxiation if ingested in cramped quarters, in addition to nausea, headaches and vomiting.
DuPont’s La Porte facility employs 320 people at its 800-acre facility and produces primarily pesticides, fluorochemicals and polyvinyl alcohol resins, according to DuPont's website.