Emergency Shutdown System

Emergency shutdown systems/valves not readily accessible. 

Emergency Shutdown Device A device that is designed to shutdown the system to a safe condition on command from the emergency shutdown system. 

Emergency Shutdown System The safety control system that overrides the action of the basic control system and shuts down the process when predetermined conditions are violated. 

Active—Using controls, safety interlocks, and emergency shutdown systems to detect and correct process deviations e.g., a pump that is shut off by a high level switch in the downstream tank when the tank is 90% full. These systems are commonly referred to as engineering controls. 

A pressure sensor giving a continuous indication which is displayed on the control panel and can be observed by the operator. The sensor has a high pressure safety interlock set at a predetermined pressure that activates an emergency shutdown system. 

The same system, but with an on-off pressure switch set to activate the emergency shutdown system if the pressure reaches the predetermined point. The pressure switch remains inactive as long as the pressure is below its trip point. 

Mitigating events or mitigating factors act to impede the accident sequence, resulting in less severe consequences. Examples include detection and activation of emergency shutdown systems, operator intervention, spill containment, equipment spacing, natural dispersion, and reducing the... 

Since the aggregate risks from Process Unit 2 are largely the result of single event—brittle fracture—the qualitative hazard assessment identified potential safeguards that could be put in place to prevent a brittle fracture occurrence. It was decided that the best option would be to install an emergency shutdown system in Process Unit 2 to prevent pressuring the nitrogen vapor vessel if a cold temperature situation was present. 

Figures 6.3 and 6.4 show the adjusted F-N curves. With this risk reduction, the company s aggregate risk criteria would be met Therefore, the emergency shutdown system was installed and no further action was required.

Consider again the alarm indicator and emergency shutdown system of Example 11-2. Draw a fault tree for this system. 

The top event is written at the top of the fault tree and is indicated as the top event (see Figure 11-14). Two events must occur for overpressuring failure of the alarm indicator and failure of the emergency shutdown system. These events must occur together so they must be connected by an AND function. The alarm indicator can fail by a failure of either pressure switch 1 or the alarm indicator light. These must be connected by OR functions. The emergency shutdown system can fail by a failure of either pressure switch 2 or the solenoid valve. These must also be connected by an OR function. The complete fault tree is shown in Figure 11-14. 

The concept of PFD is also used when designing emergency shutdown systems called safety instrumented functions (SIFs). A SIF achieves low PFD figures by... 

There are three safety integrity levels (SILs) that are generally accepted in the chemical process industry for emergency shutdown systems ... 

Each of these steps might be performed either by direct action of operations or emergency response personnel or by automatic systems. An example of the latter might be an array of toxic or flammable gas detectors that might trip an emergency shutdown system that closes remotely actuated block valves and vents off the process pressure to a flare if two adjacent sensors read above a predetermined vapor concentration. 

Introduction The chemical processing industry relies on many types of instrumented systems, e.g., the basic process control systems (BPCSs) and safety instrumented system (SIS). The BPCS controls the process on a continuous basis to maintain it within prescribed control limits. Operators supervise the process and, when necessary, take action on the process through the BPCS or other independent operator interface. The SIS detects the existence of unacceptable process conditions and takes action on the process to bring it to a safe state. In the past, these systems have also been called emergency shutdown systems, safety interlock systems, and safety critical systems. 

Active controls use engineering controls, safety interlocks and emergency shutdown systems to detect process deviations and take appropriate corrective or remedial action. Their effectiveness depends on proper selection, installation, testing, and maintenance. 

A hazard analysis may be performed to review reductions in the suggested separation distances. Increased risk can be mitigated by providing additional safeguards, such as fireproofing, automatic water-spray systems, emergency shutdown systems, or additional firefighting equipment. 

An automated, emergency shutdown system is strongly recommended to isolate and stop the loading or unloading operation in the event of overfilling, fail-... 

Where a loading system s emergency shutdown system closes a valve on gravity or pipeline fed transfer systems, care should be taken to ensure the line is protected against pressure surges or hydraulic hammers which may cause gasket blowout or line failure (NFPA 30). 

Final action taken in response to a N-E-L may be operator action or automatic action. Automatic control or emergency shutdown systems should exist when operator response cannot be completed before the parameter has reached a point exceeding the N-E-L. 

Active—Control or mitigate incidents using controls, safety interlocks, or emergency shutdown systems to detect hazardous conditions and take appropriate action to place the plant in a safe condition. 

Manual or automatic emergency shutdown systems to shut off one or more reactant feeds and then vent the contents to reduce reactor pressure ... 

Operations are also assigned independent prooftests (in addition to the split test above) which are functional trips or visual checks of controls and emergency shutdown systems. 

Type of document (e.g., instrument schedule, loop diagram, emergency shutdown system specification, temperature transmitter specification sheet)... 

The control of the nuclear and chemical reactivity in case of accidents is insured by the emergency shutdown systems. The safety function devoted to the thermal power extraction from the HYPP is directly linked to the control of the chemical reactivity because the kinetics of chemical reactions increases with the temperature. The HYPP must be cooled by emergency systems, water streaming on equipments, spraying systems, and so on. 

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