On basis of the FSL report, the Makarpura police on Wednesday registered an FIR against plant in-charge Jaswant Singh Tailor under sections 287 and 304-A of IPC for `causing death due to negligence'.

Samples of various materials collected from the mishap site had been sent to FSL. FSL scientists reported that thickness of the vaporiser no. 4 had decreased due to continuous corrosion from sulphur dioxide and lead coating of the vessel was also incomplete.

``While the vaporiser had weakened because of corrosion and partial lead coating, the pressure inside it remained the same, which lead to the blast,'' the report stated.

The FSL scientists also found that impurity in sulphur dioxide obtained from outside and excessive moisture content in it was also responsible for increased pressure in the vessel, thus causing explosion.

A report submitted by the Factories Inspectorate in the last week of December had also stated that vessel had weakened because of corrosion and needed to be replaced. ``Had the vessel been replaced after proper checking, the tragedy would have been averted,'' the report stated.

Though no one has been arrested so far, Police Inspector G J Sindhi said investigation was on.