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VI.b Gas leakage on May 11, 2021: Accident occurred due to thionyl chloride gas leakage from reactor 0101 during manufacture of Vildagliptin.
 The unit was involved in the manufacture of Vildagliptin (consented product).
 On May 10, 2021 batch was completed and night shift incharge loaded mixed liquor generated during production of vildagliptin into GLR reactor 0101. Further the night shift incharge added caustic lye into reactor 0101 for neutralization.
VI.b.i Sequence of Events and Causes of Accident 10.05.2021 : Vildagliptin batch completed. Mother liquor or 21:00 hrs aqueous layer transferred to reactor GLR 0101 11.05.2021 : Caustic lye added to reactor 0101 for 5:15 hrs to 6:00 neutralization. Shift change at 6:00 AM.

hrs Transferring of neutralized Vildagliptin aqeous layer was still pending.

11.05.2021 : Workers were experiencing odour problem. 7:00 hrs Generally the employees are facing odour issues due to which the employees could not understand that gas leakage was taking place from reactor 0101.

11.05.2021 : Workers left to canteen to have breakfast. six 8:00 hrs workers stayed back in production block-II. Since the transfer pump was under repair, transfer of aqeous layer to ETP was not undertaken.

11.05.2021 : Sh. Shareefuddin, shift supervisor instructed Sh. 8:15 hrs Bellamkonda Srinu to transfer the partially neutralized 3200 liters of Vildagliptin aqeous layer to ETP under nitrogen pressure.

11:05.2021 : Other workers have entered production block-II 8:35 hrs by wearing safety masks and shifted the affected employees from production block-II to safe zone.

11:05.2021 : Reactor vent closed. There was severe odour 8:45 hrs nuisance but till this time, the gas was not identified.

11.05.2021 : Affected workers shifted to ambulance. Safety 9:00 hrs persons were called for and based on the smell & irritation caused to nose & throat, safety persons suspected that the accident has taken place due to thionyl chloride. Reported that previously also during Vildagliptin manufacture similar odour issue was experienced due to thionyl chloride gas leakage was experienced in the unit (especially during neutralization) based on which it was concluded that the accident is due thionyl chloride.