How to Design the Emergency Relief System

Process and/or safety engineers and managers need to clearly understand, plan and execute future emergency relief system design work for plant projects, such as Process Hazard Analyses (PHA), unit expansions, debottlenecking studies etc. This article focuses on the usefulness of Design of Emergency Relief Systems (DERS), Hazard and Operability (HAZOP) and Safety Integrity Level (SIL) tools.

Chemical industry in general, deals with varieties of flammables and toxic materials on day-to-day basis – wherein the risk of exposure of people to such chemicals is always present. Handling of such chemicals from safety point of view is a major challenge for key decision makers. On one hand the industry has pressure to deliver increased production – and on the other hand it needs to ensure the process safety. Any accidental event, which arises out of failure of safety measures, causes loss of production and affects plant personnel’s health. There are various ways to mitigate such incidents, for example, properly designed pressure relief systems can save operating equipment in the event of an emergency, avoiding both capital spending to replace damaged equipment and costly downtime.

Classification of Hazardous Chemicals

Chemicals are broadly defined into three categories as per Schedule I (Part I & Part II ) guidelines of Ministry of Environment and Forests:

Part I

• Toxic chemicals
• Flammable chemicals
• Explosives

Part II

There are about 429 chemicals defined as hazardous and toxic chemicals in Part II classifications. Some of them that are widely used are – acetone, acrylonitrile, ammonia, ammonium nitrate, aniline, benzene, butane, carbon monoxide, chlorine, liquefied petroleum gas, nitrobenzene and sulphuric acid.

Emergency Systems for Process Hazards

The key to implementation of effective process safety and risk management systems lies in developing a common framework, which includes all local regulatory requirements and all corporate standards. A proactive approach, coupled with properly planned and implemented process safety management system can help minimise loss of life, environmental impact, equipment damage, citations and litigation...