A sample of the walls of a housing project tank that caved in on Saturday morning, killing three labourers, will be sent for tests to find out the exact mix of cement and sand.

Police said the test results will strengthen the grounds for the arrest of those responsible for constructing the tank at the city?s biggest residential project, on Prince Anwar Shah Road, in south Calcutta.

Sanjay Choudhury, CEO of the project, while wondering what there was to ?write about a mere incident?, claimed that efforts were on to ensure that the victims were provided with compensation in keeping with the existing laws.

A preliminary probe suggests that the walls could not bear the water pressure and collapsed. A case of ?death due to negligence? has been registered against Ahluwalia Contracts (India) Ltd, engaged by the project promoters for carrying out the civil construction work.

?Measures will be taken under the section in which the case has been filed. We need some time to sort out the nitty-gritty,? said S.N. Gupta, superintendent of police, South 24-Parganas.

While the police are taking steps that would lead to an arrest, representatives of Citu, DYFI and Nagarik Committee of ward 93 met CEO Sanjay Choudhury, and demanded a probe into the crash by an independent body, preferably by experts from the civil engineering department of Jadavpur University.

?Besides, we?ve sought a detailed report on steps being taken by the promoters and the construction company concerned to ensure safety and security of the workers. No list of the number of people employed at the site is available, not to speak of an insurance policy. We?ve asked them to provide the details and also clean up a stretch of Prince Anwar Shah Road affected by construction activity,? said Rana Mitra, a local CPM leader.

Delegation members said they were assured of an answer within the next 48 hours.

Water tanks have been constructed at the project site for the labourers to bathe in.