Two railway conservancy workers died while cleaning a covered drain near Matunga railway station on Saturday.
Shriniwas Mudgerikar, chief spokesperson, Central Railway (CR) said that suffocation due to the toxic gases might have caused their death.
The railways have ordered an internal inquiry into the death of Shaikh Husain Mohammad (55) and Shashikant Sahani (53).
Both of them were railway employees.
Mohammad and Sahani, had entered the nullah to clean it. When they did not come out of the for a long time, people called the police and the fire brigade.
The fire officials said that by the time the bodies were fished out, they were already dead.
"This unfortunate incident has happened for the first time during the railway drain cleaning," he added.
The CR cleans drains as part of pre-monsoon preparation.
The CR has announced that both families would get compensation according to the railway rules. In a similar incident, two contract labourers died by inhaling toxic gases when they entered to clean a manhole for a Brihanmumbai Municipal Corporation contractor.
Senior police inspector Lata Donde of Shahu Nagar police, in whose jurisdiction the case falls, said that a case of accidental death has been registered.
On May 20, two conservancy workers died of asphyxia after they slipped and fell inside a drain that they were cleaning at Kalachowkie as part of the municipal corporation’s pre-monsoon preparation.