Residents were told to stay indoors and shut their windows as firefighters spent four hours dealing with a chlorine gas leak.
A member of the public heard the toxic gas hissing from a small disused cylinder on industrial wasteland in Denton, Gravesend,
Firefighters were alerted to the scene in Dering Way at 4.30pm yesterday and set up a 60-metre exclusion zone while the gas dissipated into the air.
Fire crews brought in a specialist gas detection unit and paramedics attended the scene as a precaution.
By 9pm, all the gas had escaped and residents could leave their homes again.
Danny Turner, watch manager at Thames-side Fire Station, said: "We allowed the chlorine gas to disperse safely, monitoring to make sure there was no danger to the surrounding area.
"We advised local residents to stay indoors, keep their windows shut and report any health difficulties.
"Luckily it was raining and that would have assisted in not allowing any airborne gas to form. We were constantly checking the air quality.
"The attitude of local residents was good, they were very co-operative and they took what we said in the spirit it was meant."
It is not known what caused the leak but the circumstances were not thought to be suspicious.