SINGAPORE - Residents were startled by a loud bang after 45kg of chlorine powder was poured into the public sewers by a swimming school.
A maintenance keeper at the site in Jurong East had discarded it without realising it would cause a reaction.
The Happy Fish Swim School worker acted at about 8.30pm on Friday (March 5), after noticing a strong smell from the chlorine drum, which had been in contact with moist air. No injuries or damage were reported.
School founder Tan Jian Yong said the maintenance keeper "took the initiative to discard the chlorine powder into the sewage without knowing that it will cause issues".
He wrote on Facebook: "Chlorine is very reactive to germs, bacteria and other chemical compounds which can be found in general sewers. As a result, it inevitably caused a chemical reaction. A loud sound alarmed neighbouring residents."
Mr Tan said the school's operations were unaffected and classes would run safely as normal. He added that the maintenance keeper was taken to hospital for a check- up.
The Singapore Civil Defence Force said it received a call for assistance at about 8.35pm.
Firefighters used a water jet to mitigate the presence of gas produced by the chemical reaction.
A spokesman for national water agency PUB said a "large amount" of calcium hypochlorite had been discharged into the sewers. The chlorine compound is commonly used as a disinfectant or bleaching agent.
The spokesman said the mishap had not affected the sewerage system or quality of used water, which flows to reclamation plants for treatment.
"PUB is investigating the incident and continues to monitor the situation closely," he added.