The High Power Committee (HPC) constituted by the State government to probe the styrene monomer vapour leak at the LG Polymers plant on May 7 that killed 12 persons and hospitalised over 585 people, in its report stated that the uncontrolled vapour release from the M6 tank qualifies as a major accident under MSIHC Rules, 1989.
The HPC observed that a number of factors were responsible for the increase in temperature in the tank that led to auto-polymerisation and finally runaway reactions, leading to the tragedy.
Thermal stratification
The committee concluded that one of the prime factors was change in the piping design within the tank carried out in December 2019, which not only disturbed the styrene recirculation system but also led to significant thermal stratification. In other words, the top level of the styrene monomers in the tank experienced much higher temperatures than the bottom.
Also, approval was not taken from either the Petroleum and Explosives Safety Organisation (PESO) nor any other statutory organisation . The committee noted that any modification of equipment or plant should be subjected to Hazard and Operability and Risk Assessment (HAZOP) Study.
The temperature measurement in M6 tank is restricted to the bottom zone, while the top and central zones had no measurement system. Such tanks as per industry specifications, should have the temperature monitoring system at five levels.
The committee noted that the tank had overshot its lifespan. It was not subjected to any mechanical integrity assessment study and the plant had never implemented any Life Extension Programme (LEP).
PESO had accorded licence for styrene storage in 1977. The tank was built in 1967, as earlier it was storing molasses and this takes the tank’s life to 53 years, observed HPC chairman Neerabh Kumar Prasad.
The committee in its 400-page report also observed that the styrene tanks and pipelines of the LG Polymers plant are made of mild steel, which is a serious non-conformance to the laid down standards and guidelines.
Contaminants
The HPC also pointed out that the maintenance of the tank was very poor. As per the report, the last time the tank was cleaned, as per records, was in 2015. Such tanks need cleaning, visual inspection and application of appropriate coating once in every two years.
The technical committee appointed by the HPC in its report observed the presence of contaminants such as iron oxide (rust), oxidising agents, metallic hydrides, iron chlorides and other solid compounds, which probably led to the auto polymerisation. But this aspects needs further forensic study, the HPC suggested.