The victims identified as Phool Singh Sen (25), Titu Meena (25), Satpal Gurjar (40) and Madaram Gurjar (22) were cleaning the tank of a factory in Nimrana area when the incident occurred.
The body of Phool Singh was handed over to his family after postmortem.
The postmortem of remaining three labourers will be conducted tomorrow, police said, adding that the matter was being probed.