Quantitative risk assessment of anhydrous ammonia leakage and on site emergency plan at Bintulu industrial park / Nur Syamimi Mustapa

Nur Syamimi, Mustapa (2018) Quantitative risk assessment of anhydrous ammonia leakage and on site emergency plan at Bintulu industrial park / Nur Syamimi Mustapa. Masters thesis, University of Malaya.

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Abstract

Anhydrous ammonia is a pure form of ammonia and has strong affinity towards water that when a person is exposed to ammonia vapor, the vapor will cause chemical burn of skin and respiratory tract when inhaled. Objectives of this study is to quantify the risks associated with hazards of leakage of anhydrous ammonia from storage tank and to design on site emergency plans that can prevent and contain accidental leakage of anhydrous ammonia as well as minimize the impact on the workers and community at Bintulu Industrial Park. Exposure to high level of ammonia concentration of more than 300 ppm will cause death to a person. ALOHA is computer aided software that helps in predicting and estimating the impact of anhydrous ammonia leakage. This study was based on one spherical tank with storage capacity of 1000MT. The leakage was due to rupture of inlet vale with diameter of 30cm. The diameter of the tank was 14m and the location of the rupture was 7m from the ground. The tank was 85% full when the leak occurred. Anhydrous ammonia was stored as pressurized liquid at ambient temperature. During the incident, the ambient temperature was 27˚C with relative humidity of 82%. The windspeed was at 3 m/s from 10m above ground and was blowing from the West. ALOHA predicted the threat zone for dispersion of ammonia vapor cloud, flammable area of ammonia vapor cloud, blast force due to overpressure of ammonia vapor cloud explosion, jet fire and fireball due to BLEVE. The threat zone was calculated based on the LOC which hazards proved to be detrimental towards safety and health of person and also caused damage to the properties. The red zone represented the most hazardous area whereas the yellow zone represented the least hazardous area. For dispersion of ammonia vapor cloud with airborne concentration of 1100 ppm at Bintulu Industrial Park, the ammonia vapor cloud was dispersed to a distance of 9km away from the source within 60 minutes. The flammable area of ammonia vapor cloud with 60% LEL was 822m. The blast force due to overpressure of vapor cloud explosion only caused glass to shatter at 1.0 psi within an area of 555m from the source. Thermal radiations were radiated from jet fire and fireball due to BLEVE. For jet fire, the thermal radiation energy of 10.0 kW/(sq/m) radiated to an area of 53m from the source whereas for fireball due to BLEVE, the thermal radiation energy of 10.0 kW/(sq/m) radiated to an area of 660m from the source. Ammonia jet fire burned for more than one hour but fireball from BLEVE occurred only for 26 seconds. Exposure to thermal radiation energy of 10.0 kW/(sq/m) can cause death due to chemical burn of skin and respiratory tract. From the hazards identified and the risks calculated, on site emergency plan which includes the mitigation method to contain and prevent the widespread of the ammonia released into the environment. Some of the mitigation methods that can be adopted were installing water fogging equipment and carbon dioxide system to be sprayed over the ammonia vapor cloud to prevent dispersion of ammonia vapor cloud to wider area. Besides that, citric acid can be used to neutralize ammonia water run-off and soil can be used to contain the spillage or run-off liquids.

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