Four labourers lost their lives in quick succession after entering a sewage treatment plant at Virar West on Tuesday morning. According to the police, they drowned after losing consciousness due to the inhalation of poisonous gases.

The police said the first labourer, Nikhil Ghatale, 24, entered the plant to carry out a cleaning operation around 6 am. As he did not return after 15 minutes, his 27-year-old brother, Amol, also a labourer, was sent by the contractor to take a look. When neither returned, the contractor sent in Shubham Parkar, 28, around 6.20 am. Ten minutes later, when all three failed to surface, a fourth person, Sagar Tendulkar, 29, was tasked with seeing what had happened.