(104bp) Quantitative Risk Assessment Study of Hydrogen Cyanide handling areas of Acrylonitrile Plant

The paper aims at describing the study, methodology and the findings of the Quantitative Risk Assessment (QRA) conducted for Hydrogen Cyanide (HCN) in Acrylonitrile Plant.

HCN, a highly toxic chemical, is produced as a by-product in the Acrylonitrile Reactor and the toxicity possesses significant hazard to the employees and community. Though HCN is both toxic and flammable, only toxicological property of HCN has been addressed in this report as the impact potential of toxicity is greater when compared to its flammability.

This study provides valuable insights into the safe handling features of the plant, highlighting those areas where a loss of containment may result in harm to plant, personnel at the facility, public, and the environment.

The study is a systematic approach of identifying and eliminating/ minimizing hazards posed by HCN. It includes the following stages: Selection of the unit for study, Data Collection, Hazard Identification, Analyzing Past Incidents and their Investigations, Selection and Node Segregation, Node Inventory Calculation, Scenario Identification, Consequence Analysis and its interpolation with windrose and Population Data, Risk Calculation and finally Recommendations for effective Risk Management.

The Study was conducted for areas handling HCN concentration > 6%. The Hazard Identification was done based on a Safety Review Checklist, Process Hazard Analysis (PHA), Past Incidents and Dow’s Chemical Exposure Index (CEI) method. Based on the Hazard Identification, scenarios were identified for Consequence Analysis (CA) and Dispersion Modeling which was done using Process Hazard Analysis Software Tool (PHAST) by M/S DNV. The Risk Rating was done based on the onsite and offsite impacts of the scenarios, the frequency of the occurrence of the scenarios and interpolating the windrose data and actual population data surrounding the plant with the Dispersion Models.

Fault Tree Analysis of the “Worst Case” scenario has been carried out to pinpoint the exact vulnerable area/ system and apply appropriate safeguards.

The study revealed vulnerable areas for HCN release in the plant. Based on the risk analysis study, suitable recommendations were made to lower the Risk.

The study was conducted by 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.

Competency development initiatives such as this were helpful in understanding of process hazards by the plant operating staff and helped in implementation of mitigating measures. Thus a robust safety management culture can be instituted.