“…The chemical was methyl mercaptan, which is used to give natural gas its rotten-egg smell.

The chemical can cause severe respiratory, skin and eye irritation. It can also cause headaches, dizziness, nausea, vomiting, coma and even death. Exposure in poorly ventilated, enclosed, or low-lying areas can result in asphyxiation, according to the Agency for Toxic Substances and Disease Registry.

Discharges, spills or accidental releases of 100 pounds or more of methyl mercaptan must be reported to the Environmental Protection Agency.”chron.com