Report on LG Polymer styrene gas leak, R. R. Venkatapuram village, Visakhapatnam, Andhra Pradesh, 28/05/2020
Report dated May 28, 2020 of the Joint Monitoring Committee constituted by the National Green Tribunal in the matter of Original Application No. 73/2020 regarding gas leak of styrene at LG Polymers Chemical Plant in R. R. Venkatapuram village, Visakhapatnam in Andhra Pradesh in compliance of NGT order of May 8, 2020.
The committee appointed to look into the matter visited the gas leakage site along with Andhra Pradesh Pollution Control Board officials and interacted with the industry officials.
On May 12, 2020, the NGT committee conducted a public consultation meeting with NGOs, residents from affected villages and industrialists. Justice B. Seshasayana Reddy, former judge, Andhra Pradesh High Court visited the site along with the committee members and APPCB officials and prepared an interim report to NGT on May 17, 2020 and a consolidated report on 28 May, 2020.
Sequence of Events
The unit was closed on March 24, 2020 and started preparations for its proposed resumption of operation on May 7, 2020, On the early hours of May 7, 2020 at about 3.00 am the tank with 1830 tons of storage had developed the leak of the styrene vapours from the top of the tank and spread beyond the factory boundary towards the west side due to wind direction and affected the residents of five nearby areas namely Venkatapuram, Venkatadri Nagar, Nandamuri Nagar, Pydimamba Colony and BC & SC Colony.
It appears from an examination of nearby damaged trees that the gas plume moved at a height of about 0-20 feet from the ground towards the nearby settlements, Causes of failure and authorities responsible The industrial unit has been closed since March 24, 2020 due to COVID-19 lockdown. As on the day of lockdown, the raw material, Styrene was available in 4 storage tanks in the factory with the inventory of 1830 tons, 2725.9 tons, 242.6 tons, 242.5 tons. The unit was permitted for daily maintenance activities during the lockdown period with 15 persons per each shift with a total of 45 personnel working every day. On the early hours of May 7, 2020 the tank with 1830 tons of storage had developed the leak of the styrene vapours from the top of the affected tank, Tank M6.
The leaked tank was old and did not have temperature sensors at middle and top surface of the tank except only provisions to measure the temperature at the bottom of the tank where refrigeration was provided. Due to lockdown, the storage tank was stand still. The styrene polymerises to polystyrene even at ambient temperature, in the absence of inhibitor, which itself is an exothermic reaction with very slow reaction rates. Although the reaction rates are slower, it will cause major operation issues, because of heat liberation and blockages in the tank. As the temperature rises, styrene starts vaporizing. The pressure in the storage tank will progressively increase, and the safety valve released the styrene vapour into the atmosphere.
The increase in temperature and pressure was not observed by the industry. Had the safety valve failed, the whole tank would have been exploded and a still bigger catastrophe would have happened. The leaked tank did not have any provision for measuring the vapour space temperature and due to this, building up of temperatures in top surface was not noticed by the industry. This was negligence on the part of the industry.
Root cause analysis showed that the problem possibly began on April 20, 2020 when the polymer concentration in Tank M6, which was idled at full capacity since March 25 post lockdown. It is known that styrene monomer can exhibit reaction runaways because of their exothermic and auto-accelerating nature even at adiabatic conditions. Mitigation of the impact could have been more effective had the chillers servicing Tank M6 been running. It was switched off at 5 pm earlier that evening as per routine site practice as ambient night temperatures required little or no chilling. There was also no automated sprinkler arrangement for vapour loss as this had never been anticipated the fire water sprinklers had to be manually activated. Another reason for the accident, TBC (inhibitor of the polymerization reaction) was not effective after liquid styrene temperature in storage rises above 52°C. Under these conditions, a short-stopper chemical should be added. But,LG Polymers did not consider this possibility. Also, no TBC was topped up in the affected tank M6 since April 1, as there was no stock at site and the tested TBC level of the contents was apparently in range.
The report said that the TBC level was not a good indicator of safety margins, the polymer content is a better measure for early alert. It takes considerable amount of idle time to have polymerization inside tank if effective inhibition and chilling is maintained.
The root cause thus appears to be the lack of experience of LG Polymers India and their Korean principal, LG Chem in monitoring and maintaining full tanks of styrene that were idled for a long period of several weeks without operation. Further, 6 was an old tank in design terms and this possibly contributed to the problem.