Concept
An industrial safety system is a countermeasure crucial in any hazardous plants such as oil and gas plants and nuclear plants. They are used to protect human, industrial plant, and the environment in case of the process going beyond the allowed control margins. As the name suggests, these systems are not intended for controlling the process itself but rather protection. Process control is performed by means of process control systems (PCS) and is interlocked by the safety systems so that immediate actions are taken should the process control systems fail. Process control and safety systems are usually merged under one system, called an integrated control and safety system (ICSS). Industrial safety systems typically use dedicated systems that are SIL 2 certified at minimum; whereas control systems can start with SIL 1. SIL applies to both hardware and software requirements such as cards, processors redundancy and voting functions. There are 2 main types of industrial safety systems in process industry: Process safety system (PSS) or process shutdown system (PSS). Safety shutdown system (SSS): This includes emergency shutdown (ESD) and emergency depressurization (EDP) systems. A third system also exists which acts as a barrier and contains the spray out of hot oil & gases from flanges, valves & pipe joints. These systems are popularly known as safety spray shields and flange guards. The use of spray guards is mandated by OSHA. These systems may also be redefined in terms of ESD/EDP levels as: ESD level 1: In charge of general plant area shutdown, can activate ESD level 2 if necessary. This level can only be activated from main control room in the process industrial plants. ESD level 2: This level shuts down and isolates individual ESD zones and activates if necessary EDP. ESD level 3: provides "liquid inventory containment". The safety shutdown system (SSS) shall shut down the facilities to a safe state in case of an emergency situation, thus protecting personnel, the environment and the asset.
