Emergency Shut Down (ESD): Safety in Critical Situations

Prevent hazardous situations from causing unsafe incidents

A vital layer of protection, an emergency shutdown system is key for providing safe operations. If hazardous conditions occur, immediate action must be taken. Shutting down the facility to a safe state protects personnel, the environment, and the asset.

Emergency Shutdown (ESD) System?are specialized highly reliable control systems for high risk industries like Oil and Gas, Nuclear Power or other Environments with explosion risk (Ex.). Their purpose is to protect personnel, plant, and the environment in case the process goes beyond the control margins.

A critical condition for which immediate?shutdown?of the?gas turbine and compressor is required and delayed shutdown options are not acceptable because of the danger posed to the compressor station, human life or physical damage to the equipment.

Emergency Shutdown System (ESD)?is designed to minimize the consequences of emergency situations, related to typically uncontrolled flooding, escape of hydrocarbons, or outbreak of fire in hydrocarbon carrying areas or areas which may otherwise be hazardous.

There are several purposes of the ESD System which is:

• Protection of personnel
• Protection of the environment
• Minimize loss of production and damage to plant assets

Typically, the ESD System could fulfill the above objective by the following implementation:

• Monitoring of an operational or equipment condition
• Automatic action in case of process hazardous conditions is exist by de-energizing electrical equipment, shutting down and/or isolating process equipment and, isolating and depressurizing the installation.
• Enabling manual initiation of ESD actions through ESD push button all around the plant.
• Monitoring the Fire & Gas conditions (F&G) by the F&G System
• Automatic action in case of F&G hazardous conditions exist by providing audible and visual alarms for personnel.

Typical Actions from an Emergency Shutdown System

• Shutdown of part systems and equipment
• Isolate hydrocarbon inventories
• Isolate electrical equipment
• Prevent escalation of events
• Stop hydrocarbon flow
• Depressurize / Blowdown
• Emergency ventilation control
• Close watertight doors and fire doors
• Centralized Project Development for Both Safety and Process Needs

Emergency Shutdown system design considerations

The design of the Emergency Shutdown or ESD system shall take into account the needs resulting from normal operation and shall also fulfill the requirements that may arise during other possible (and likely to occur) abnormal or down-graded configurations. Depending on the type of operating plant and functions, ESD system design will vary.

However, the below-listed issues shall be adequately addressed when relevant:

• Tripping or stopping a unit or equipment does not necessarily eliminate all sources of hazards.
• Due to the loss of essential utilities like air, essential power, hydraulics, etc. new hazards can appear anytime. The emergency shut down system should be designed to identify and mitigate or alarm regarding the risk of such hazards.
• All operating configurations that the ESD system generates shall be stable, safe, and reversible.
• The ESD system shall be compatible with the re-start philosophy. The inevitable inhibitions of the control and safety systems during the re-start sequence shall be identified, and shall be limited in number, time, and duration.
• ESD system design shall provide specific attention to non-routine operating conditions, simultaneous operations, and down-graded situations.
• Particular operating conditions may require a different shutdown logic than that, or the combination of those, applicable under normal circumstances. For example, An installation normally operates under different conditions, e.g. high, medium, or low pressure. Each condition may require a different ESD logic, but the differences shall be limited to process shutdowns. Emergency shutdowns shall result in the same actions independent of the condition. Before switching over between different ESD logics, the proper line-up of equipment and the status of valves need to be verified.
• The Emergency Shutdown system shall be used to continuously monitor the safety parameters of the plant and shall take actions to maintain the safety of the plants on demand.
• The ESD system diagnostics shall show the following minimum fault / healthy state status but not limited to:
• Circuit breakers tripped
• Power feeders healthy
• Fuse Failure
• Power supply removed
• CPU fault
• Battery failure
• Power supply failure
• Communication Failure
• Input/ Output Module failure
• Input/ Output Module removed
• Each channel failure
• Panel internal temperature high
• Others as supplied by the manufacturer.

Working of Emergency Shutdown System

An emergency shutdown system works by monitoring the plant condition using field mounted sensors, valves, trip relays, and inputs to a control system as alarms. The control system performs a cause and effect analysis of the above parameters to determine plant health. The system will minimize the effects in case of abnormal behavior by reducing the number of plant items available or shutting down part of the systems. For example, In case of a fire hazard, a Fire Damper control system may override the existing controls to open or close vents as needed, and close fire doors.

Normally, for plants, a shutdown matrix is defined. Three to four shutdown levels based on decreasing criticality are decided and the complete plant is categorized. In the process control system, various safety loops and devices are organized as complementary barriers.