Critical instrument system

Rationale for critical instrument systems should be documented. 

All critical instruments/systems, alarms and performance indicators must be maintained in accordance with established preventative maintenance procedures. Consider specialized preventative procedures for activities within this band... 

Another Company—A Different Emphasis on Safety Critical Instrument Systems... 

The criteria by which the truly critical instrument system can be characterized as such, and distinguished from other important (but not critical) systems should be documented. 

Percentage of critical instrument systems found to be defective or miscalibrated... 

In the past, safety applications were called "critical instrument systems". Engineering rules, typical examples and best practices as well as test procedures were developed. 

List (if available) of critical alarms, trips, interlocks, critical corrective actions and other critical instrument systems to validate reliability... 

Another company - a different emphasis on safety critical instrument systems... 

It is also used for critical instrumentation systems. Fire losses can be minimized by keeping essential control circuitry operational during the early stages of a major fire and by minimizing shutdowns resulting from minor... 

Another critical instrument specification is the total extra-column dispersion. The subject of extra-column dispersion has already been discussed in chapter 9. It has been shown that the extra-column dispersion determines the minimum column radius and, thus, both the solvent consumption per analysis and the mass sensitivity of the overall chromatographic system. The overall extra-column variance, therefore, must be known and quantitatively specified. 

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. 

The distributed control system (DCS) hardware areas are often referred to as "process computer rooms." I/O Rooms contain the incoming and outgoing wiring, cables and data highway links, and often small transformers and other related electrical equipment. Often, additional space is needed for a master process engineering computer terminal/work station for process control system changes and for critical safety instrumented systems (SIS) for interlocks and emergency shutdowns. 

The integrity of safety instrumented systems is usually dependent on proof testing at specified intervals (often at a frequency between monthly and three-monthly). Safety management systemst2jsafety critical operating procedures such as described in (c) above are adhered to. 

A Critical instrument is a device and its accompanying system whose proper functioning is necessary to prevent a serious incident. The system that reads the signal, interprets it, and displays it is as critical as the device that generates the signal. 

A serious incident is one in which serious personal injury or serious health, environmental, or economic damage could occur. Some examples of critical instruments and instrument systems are ... 

Once a critical instrument loop is identified, a procedure for testing the entire loop must be written. The test procedure will influence the design of the new system, since, if possible, the test should be an actual performance test. For example, if a high temperature should close a valve, the ideal test would consist of raising the temperature to see if the value closes. Efforts should be made to avoid test procedures which require temporary wiring disconnects, valve closures, and so on, which might not be returned properly to operating condition. 

As described above, performance testing is an important consideration in the design of a critical instrument loop. Components of the system must be selected for ease of testing, as well as for their ruggedness and reliability. 

In computer systems, program logic is an important component of the critical instrument loop. Security precautions must be taken to prevent inadvertent changes in programming. In addition, manual overrides are discouraged. For example, if it is critical to shut down a pump during an emergency situation, a manual on switch may not be desirable. 

Process/system critical instrument—where failure may have a direct effect on process or system performance without affecting final product quality or safety. 

Calibration of critical instruments and system components must be controlled by a calibration schedule in order for call-off dates to be determined. The calibration periodicity should be determined by the process owner, its quality representative, and the maintenance engineer, taking into account the manufac-... 

Conditional on satisfactory on-site inspection, assembly, installation, SAT, critical instrument calibration, and design qualification, the computer system is available for the in situ qualification phases. 

The decommissioning procedure must address both operational and safety aspects of the computer system application and establish integrity and accuracy of system data until use of the system and/or process is terminated. For quality-related critical instrumentation, proof of calibration prior to disconnection is needed. 

Critical instruments assigned a Class 1 include those necessary to avoid a failure which may cause the perils listed above or instruments which fail to inform of upset conditions which may result in perils. Testing of these instrument systems may be mandated by regulatory agencies, in-house technical safety review committees, HAZOP studies, or designated as critical by operations supervisors. All of these shutdown systems and alarms must be prooftested in accordance with a proper schedule. [8]... 

Serious Consequences—Class 2. Equipment or the critical instruments serving equipment whose failure could possibly cause, or fail to warn of upset conditions, uncontrolled releases of dangerous materials, situations that could result in accidental fires and explosions. Furthermore these failures could result in serious conditions involving environmental releases, property or production losses, or other non-life-threatening situations. These particular pieces of equipment, the safety shutdown systems and the alarms that serve this equipment are given a slightly lower priority. However, they are also inspected, tested, or prooftested on a regular schedule, but may be allowed to have some leniency in compliance. 

Normal Consequence—Class 3. All other containment equipment or instrumentation serving the operation whose failure could result in minor environmental releases, property or production losses, or injury to personnel or reduced economic life. It may include less critical refrigeration systems, turbine overspeed trips, lubrication system alarms and similar important, but not crucial items. 

Alarms, process safety interlocks, and safety instrumented systems can be modified easily by aging or tampering and such critical safeguards are just too vital to neglect. Each organization must develop an effective way to ensure that process safety systems will properly function when the process demands protection. 

The Safety Instrumented Systems (SIS) and critical alarms assigned a Class 1 include those that have been mandated as such by state or federal agencies an in-house technical safety review committee HAZOP studies and specific alarms deemed critical by operations supervisors. All of these Safety Instrumented Systems and alarms are on a regular prooftesting schedule. 

Class 1 safety instrumentation loops include alarms and trips on storage tanks containing flammable or toxic liquids, devices to control high temperature and high pressure on exothermic-reaction vessels, and control mechanisms for low-flow, high-temperature fluids on fired heaters. Other Class 1 instruments include alarms that warn of flame failure on fired heaters, and vapor detectors for emergency valve isolation and sprinkler-system activation. All of these alarms, shutdown valves, and other critical instruments are regularly proof-tested to a well-defined schedule. 

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