The Coast Guard said ammonia that leaked from a vessel forced the closure of the Houston Ship Channel and nearby bridges while sending four workers to a hospital.
Coast Guard officials said in a release that the tanker Sombeke was docked at the Houston Ammonia Terminal on Friday evening when a gasket blew and anhydrous ammonia leaked.
The tugboat Trigger was refueling the Sombeke when the leak occurred, and four of its crewmembers were exposed and required hospitalization.
The closure of the channel as well as the Interstate 610 and Beltway 8 bridges lasted about 90 minutes.
Authorities had alerted nearby residents to remain in their homes.
A hazardous materials team determined the leak was "minor."
Anhydrous ammonia is a pungent gas that's used as a fertilizer.