(81bs) Quantitative Risk Assessment for Hydrofluoric Acid Handling Unit

The paper describes the Quantitative Risk Assessment (QRA) study conducted for Hydrofluoric acid (HF) handling unit of Linear Alkyl Benzene (LAB) plant.

The objective was to carry out QRA study of the HF system and build in-house capability to carry out such studies. Alkylation unit of Linear Alkyl Benzene (LAB) plant uses Hydrofluoric acid (HF) as the catalyst which is highly toxic and the high inventory of acid in the unit poses a significant hazard.

Though the unit handles both toxic and flammable substances, this study addresses toxic effects of HF release as impact potential is higher for a toxic release even in case of a minor release.

The study covers the following stages: Hazard Identification, Consequence Analysis, Frequency Analysis, Risk Analysis and Risk Assessment and Management. Hazard identification was carried out by Safety review and Dow's Chemical Exposure Index (CEI) method. Safety Review was conducted based on a checklist prepared against the requirements of API-751(Recommended Practices for Safe Operation of Hydrofluoric Acid Alkylation Units). Inventory calculations for the unit were carried out and CEI was calculated for screening of loss of containment scenarios. Based on the Safety Review, CEI rating and Incident history, scenarios were selected for consequence analysis. Based on onsite and offsite impact, frequency of loss of containment scenarios was considered. Risk was evaluated for the postulated loss of containment scenarios based on frequency and consequence of HF release incidents. Actual onsite and offsite population and meteorological data were gathered and suitable assumptions were taken to arrive at the risk values for each scenario.

The study revealed vulnerable areas for HF release in the unit e.g., acid unloading hose and small bore piping. Based on the risk analysis study recommendations were provided to bring down the risk level. The study findings have been useful in deciding additional safeguards, updating emergency response plan, standard operating/maintenance procedures, etc. as appropriate.

The study team comprised a multi-disciplinary team from the plant, assisted by the corporate QRA resources. The study resulted in development of in-house competency in QRA study and ability to translate such study findings into suitable risk reduction measures.