The Joint Monitoring Committee (JMC) constituted by the National Green Tribunal (NGT) to inquire into the leakage of styrene monomer vapour from a storage tank in LG Polymers, a chemical plant owned by South Korea-based LG Chem, located at R.R. Venkatapuram village here has noticed many lacunae in the functioning of the plant.
Styrene vapour leaked in the early hours of May 7. Twelve persons had died and 580 were hospitalised in the incident.
The JMC, led by former High Court judge B. Seshasayana Reddy and comprising Ch.V. Rama Chandra Murthy, former Principal of Andhra Medical College, P. Jagannadha Rao, professor of chemical engineering in Andhra University, K.V. George, Scientist at NEERI-Nagpur, and Shaik Basha, Scientist and Head of CSIR-NEERI, Hyderabad, has found at least five glaring lapses in the plant.
‘TBC stock insufficient’
The committee has reported that tertiary butyl catechol (TBC), which is used as polymerisation inhibitor and to lower the temperature in tank, was in insufficient quantity at the time of the accident.
“Styrene monomer is a Class B petroleum product and it needs to be stored at a temperature ranging between 15° and 18° Celsius. At no point should the temperature exceed 25° degree Celsius,” said Prof. Jagannadha Rao.
“To achieve it, apart from using the refrigeration technique, TBC is added. Since TBC stock was insufficient, styrene monomer could possibly have reacted inside the tank, triggering polymerisation, which in turn resulted in formation of vapour. The vapour, then in thick viscous form, leaked out of the tank, ” he said.
The JMC also pointed out that there was no system to monitor the dissolved oxygen in the vapour space, which might have fallen down to below 6%.
“Oxygen falling below 6% is a clear indication of self-polymerisation, and there is no mechanism to notice it. The plant was under lockdown for over 45 days, and the reaction could have started at least one week or 10 days ahead of the incident,” he observed.
‘No apparatus to monitor temperature’
The tank was an old one and did not have temperature monitoring apparatus in the middle and top levels. It had a monitoring system in the lower level. But the second tank, which was said to be a new one, had the apparatus at all the levels.
The reading at the bottom level showed 17° Celsius at the time of the incident, but the temperature might have soared in the upper part, the report said.
“To keep the temperature of styrene under control, it needs to be in circulation. But due to the lockdown, it was stagnant, which probably led to the Deils-Alder type reaction, resulting in self- polymerisation. Since there was no apparatus to record the change in temperature in the upper part of the tank, styrene reached its onset temperature, which is 66° C over a period of time. And once it touches the onset temperature, it takes 15 to 20 minutes to reach its boiling temperature, which is 145° C. As per our findings, this probably was how the vapour formed and leaked,” Prof. Jagannadha Rao said.
As per the experts, the refrigeration for styrene storage should run 24/7. But, as per the NGT report, the system was not operated for 24 hours prior to the incident.
The report also attributed the incident to gross human failure and negligence of the person in-charge of the plant and maintenance personnel of the storage tank.
Published - May 30, 2020 12:16 am IST
