Simulation of atmospheric dispersion of Styrene Gas leak accident at LG Polymers Visakhapatnam using Buoyancy modified FLEXPART-WRF model

The FLEXPART-WRF model is modified for buoyant gases and used in the Chemical Emergency Response System (CERS) for chemical impact and consequence assessment for decision support in the event of accidental releases at industrial sites. In this work we validate this modified dispersion model by simulating the Styrene gas leak accident at Visakhapatnam, India. We configure the domain with 1km grid resolution and 6-hourly NCEP-FNL data at 0.25°. Data of local meteorological condition, release rate, concentration levels, threat zone etc. are available from High-Power Committee Report (HPCR) of Andhra Pradesh Government. Simulation shows agreement with estimates by HPCR in terms of prevailing wind direction towards North-Northeast, prevailing Pasquill-Gifford stability category of E and F during the initial accident hours. Simulated temperature and humidity also show good agreement with local station data and radiosonde data. The simulated concentration levels with buoyancy corrected model, corresponding to Acute Exposure Guideline Level-3 (> 1500 ppm) and Level-2 (100-1000ppm) is distributed within ~ 430m and ~ 1100m from the release location. These identified distances from the simulation agree reasonably well with HPCR estimates of ~ 398m and ~ 1144m using USEPA’s ALOHA gas dispersion model. The study also finds excellent agreement with concentration time-trend as measured at two locations in north-east and north-west direction from release location during the accident. The present study hence enhances confidence in using the modified FLEXPART-WRF model for buoyant dispersion events.