Proceedings of CUChE Alumni Symposium 2022
On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”
CUChEAA ISBN: 978-81-954649-1-3
December 2022 P a g e | 32 Volume 2, Issue 1
Societal Risk Assessment of Styrene Release Scenario – A case study
Diptendu Das* and Ramdas Bhattacharya**
*Atomic Energy Regulatory Board (AERB), Mumbai
**Former Director and Vice Chairman, AERB
Email: diptendudas@aerb.gov.in, dir.ipsd@gmail.com
Abstract
A societal risk assessment study has been carried out to validate the consequence effect distance and to estimate worst case
scenario effect of styrene gas release recently from a polymer chemical plant near Visakhapatnam, India. Significant
quantities (about 820 MT out of 1842 MT) of styrene stored in a tank (tank capacity 3090.96 KL/ 2250 MT) leaked into
the environment. Considering the toxic nature of styrene vapour, a study has been carried out on different leak scenarios
including worst case scenario and its subsequent dispersion (heavy gas dispersion) to find out the effect distances.
The styrene vapour release scenario is simulated using Areal Location of Hazardous Atmospheres (ALOHA) Software.
Various Scenarios of releases are assumed, and different wind speeds and stability classes are considered to simulate the
scenarios. Based on the site map of the incident spot (point source of release) threat zones are generated. The effect
distance and postulated exposures on population and inhabitants around the vicinity of the site of release is studied. The
emergency preparedness and disaster mitigation measures to handle such emergency are assessed from the above study.
Study reveals that as the temperatures of the styrene gas increases from 20
o
C to 149
o
C due to polymerisation runaway
reaction the effect distance increases. It is estimated that at the worst-case scenario, a radius of 7km distance can get
affected at this temperature of release and population and other living beings and environment can get affected, if proper
mitigation measures were not in place.
It is worth mentioning that maintaining styrene below 20
o
C and preventing polymerization reaction is essential failing
which such accident can take place. In this case, cooling was not efficient, resulting in polymerization of styrene which is
exothermic in nature and runaway reaction took place causing the accident. This accident resulted in 11 fatalities and
thousands other got affected.
The worst case scenario considered in this study would help the plant authorities as well as the regulators for putting
adequate emergency planning and disaster management in place depending on this consequence effect distance and risk
assessment study.
Keywords: Societal Risk, Chemical Disaster, Styrene Vapor Leak, Wind Stability
1. Introduction
Styrene vapour release occurred in the early morning of
7th May 2020, from a polymer chemical plant near
Visakhapatnam, India. This Styrene vapour uncontrolled
release occurred from one of the Styrene storage-tanks
(M6 Tank). 11 fatalities were reported subsequent to the
release and inhalation of the toxic gas and around 600
people got affected due to styrene exposure. As per the
Manufacture, Storage and Import of Hazardous
Chemical Rules (MSIHC) Rules, 1989 this accident falls
under the category of major accident. This accident is
analyzed and various scenario are simulated to find out
effect distances for same accident as well as for other
probable conditions.
Release of any stored chemical can be of two types:
a) A common type of leakage due to faulty valves
or due to small hole in the cylinder.
b) A major release due to bursting or rupture of a
cylinder (tank), which is commonly termed as
catastrophic failure and the most unlikely event.
It is therefore necessary to estimate the distances where
the effect of toxic chemicals pose detrimental effect to
the health of the exposed individuals due to toxicity.
Continuous leakages (plume) may be treated by using
conventional atmospheric dispersion model with