CHELSEA, MASS. (WHDH) - Dozens of Firefighters and hazmat crews responded Tuesday morning to an MWRA sewage treatment facility in Chelsea after readings in the building tested positive for hydrogen cyanide and hydrogen sulfide.
Officials rushed to the facility on Marginal Street after an alarm went off around 4 a.m. Hydrogen cyanide is a colorless, extremely poisonous and flammable chemical compound.
Crews shut down power in the building, which is under construction. At least 28 construction workers were evacuated and the building was left to air out.
It’s not clear where the chemicals came from, but officials said the sewage flow may have played a role.
Remote monitors were installed in the building to allow workers back inside. Safety crews will remain at the building as precaution.
No injuries were reported. The incident is under investigation.
(Copyright (c) 2026 Sunbeam Television. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)