Process control and safety systems are usually merged under one system, called 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.

Types of industrial safety systems

There are three main types of industrial safety systems in process industry

• Process Safety System or Process Shutdown System, (PSS).
• Safety Shutdown System (SSS): This includes Emergency Shutdown-(ESD) and Emergency Depressurization-(EDP) Systems.
• Fire and Gas System (FGS).

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" and is

SSS

The safety shutdown system shall shutdown the facilities to a safe state in case of an emergency situation, thus protecting personnel, the environment and the asset. Safety Shutdown System shall manage all inputs and outputs relative to Emergency Shut Down (ESD) functions (environment & personnel protection). This system might also be fed by signals from the main fire and gas system.

FGS

The main objectives of the fire and gas system are to protect personnel, environment, and plant (including equipment and structures). The FGS shall achieve these objectives by:

• Detecting at an early stage, the presence of flammable gas,
• Detecting at an early stage, the liquid spill (LPG and LNG),
• Detecting incipient fire and the presence of fire,
• Providing automatic and/or facilities for manual activation of the fire protection system as required,
• Initiating signals, both audible and visible as required, to warn of the detected hazards,
• Initiating automatic shutdown of equipment and ventilation if 2 out of 2 or 2 out of 3 detectors
• Initiating the exhausting system.

ESD

Emergency Shutdown-(ESD) systems are aimed at isolating (closing) any hazardous valves in a process due to abnormal conditions.

EDP

Due to closing ESD valves in a process, there may be some trapped flammablefluids, and these must be released in order to avoid any undesired consequences (such as pressure increase in vessels and piping). For this, emergency depressurization (EDP) systems are used in conjunction with the ESD systems to release (to a safe location and in a safe manner) such trapped fluids.

PSV

Pressure safety valves or PSVs are mechanical devices and are usually used as a final safety solution when all previous systems fail to prevent any further pressure accumulation and protect vessels from rupture due to overpressure.