Quantitative Risk Assessment for Accidental Release of Ammonia from Fertilizer Process Plant

Quantitative risk assessment is currently popular in the industrial sector over the past
fifteen years. The application of Quantitative Risk Analysis for this study is to achieve
several objectives that are, to determine the risk of an existing of an ammonia process
plant, to ascertain the effects of accidental release of ammonia at different concentration
and to propose risk reduction measure during design or operation stage. The subject of
this study is PETRONAS Fertilizer Kedah (PFK) that has experienced on accidental
release of ammonia. This study is focused on the toxicology and explosion aspects. The
methodology for this study was literature survey and using SAFETI (Software for
Assessment of Flammable, Explosive and Toxic Impacts) with real plant data. SAFETI is
the main tool and has wide function for risk/consequence/risk and consequence studies.
As for this study, the risk analysis was run through a combination of several data (plant
layout and location, ammonia and methane properties, and atmospheric parameter) and
manipulated with assists of SAFETI in achieving the objectives. After defining the
boundaries of the system to be analyzed, this study identifies the hazards, risk level and
suggest with mitigation action. Based on the frequency of accidental events, the model of
consequence will be analyzed. From Societal Risk FN Curve, the case is lies in the alert
region. Therefore, there is requirement of Quantitative Risk Analysis. The highest risk
level is IE-5 per year for 0.7 km distance from the hazard source and the lowest risk level
is lE-9 per year for 2.5 km distance from the hazard source. Generally, in dispersion
graphs of ammonia, as the downwind distance increases the centerline concentration are
decreases. For 2 inches and 3 inches leak diameter, there is unique trend where the
centerline concentration increases back after a several period due to vaporization of spill.
In probability of fatality graph of ammonia for four weather conditions, the probability of
fatality decreases with the increasing downwind distance. Weather I is the worst case
since the probability of fatality is the highest and reach the furthest distance than other
weather condition. For explosion, the dispersion graph of methane show similar trends as
ammonia dispersion graph. However the cloud radius only 16.3 m and the BLEVE radius
is 29.81 m. Mitigation actions are proposed to lessen the risk. By inherent safety, the mitigation actions are to use small amount of ammonia and methane, to produce and
consume the substance in-situ, and to reduce the process pressure and temperature to less
hazardous condition. By engineering design, the mitigation action is to locate a dike at
0.52 m from the hazard sources. By emergency response, the mitigation action is to
develop an emergency plan on how fast people should react. A few recommendations
can be made for this study which is, to study the alternative to use lower energy material,
to analyze the possibility of unusual wind condition, and to study the toxicology of long
term effects to the agriculture activities and products.