Scope[ edit ] The process industry sector includes many types of manufacturing processes, such as refineries, petrochemical, chemical, pharmaceutical, pulp and paper, and power. The process sector standard does not cover nuclear power facilities or nuclear reactors. IEC covers the application of electrical, electronic and programmable electronic equipment. While IEC does apply to equipment using pneumatic or hydraulic systems to manipulate final elements, the standard does not cover the design and implementation of pneumatic or hydraulic logic solvers.
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Important functional safety standard for automation in the computer age Fast Forward Functional safety for process has always been a priority, and, as automation has moved into the computer age, new safety issues have arisen. The need for improved understanding and harmonization of risk reduction approaches became evident from such major catastrophes as Seveso Italy , Bhopal India , Flixborough U.
The International Society of Automation ISA recognized the need for an improved approach in handling process sector functional safety issues and developed ISA as an important functional safety standard for automation in the computer age.
By William Johnson, Richard R. Dunn, and Victor J. Maggioli Introduction This overview outlines key elements of the ISA84 committee on process sector functional safety, including scope, purpose, history, and technical issues. Background Functional safety within the process sector has always been a priority. As the process sector moved into the computer age, new issues arose as manufacturing plants converted to computer control to replace electrical, pneumatic, and electronic controls.
The process sector developed a variety of tools to address these problems, but safety performance did not always meet expectations. The need for improved understanding and harmonization of risk reduction approaches became evident with the occurrence of such major catastrophes as Seveso Italy , Bhopal India , Flixborough U. These regulations helped define areas that must be addressed in order to achieve a mandated level of functional safety performance in industry.
The International Society of Automation ISA, formerly Instrument Society of America recognized the need for an improved approach in handling process sector functional safety issues.
During the late s, more than sixty experts from diverse backgrounds including end users in the chemical petroleum industries, integrators, equipment manufacturers, consultants, and safety regulators joined ISA84 to bring together their expertise in addressing process sector functional safety.
Contributions from each of these organizations and others played significant roles in this effort. Establish criteria for, and means of assessing, reliability and availability in practical applications. Provide general specification guidelines that facilitate understanding. Provide guidelines for process safety applications requiring high reliability.
This work does not apply to nuclear power safety-related systems. Safety life cycle The ISA84 committee set out to define the boundaries of its work by developing a safety instrumented system SIS safety life cycle see Figure 1 , which illustrated the activities involved when addressing process sector functional safety.
ISA84 then selected those activities to be addressed in its proposed standard i. Concurrent with the work to develop ISA At about that time, the HSE of the U. While this approach was already in use in parts of the U. For example, IEC planned to develop a standards committee to address process sector functional safety i. ISA84 began pursuing these goals after publication of U. The impact of IEC on the safety life cycle is reflected in Figure 2.
Note that IEC functional safety standards have an expanded scope that addresses all life cycle phases i. Terminology for this effort required a strong commitment by ISA84 to introduce technical terms that would be globally accepted. The standards development required the integration of both quantitative and qualitative measures to ensure SIS designs had the ability to achieve their projected performance. This TR served two essential purposes: It illustrated various quantitative and qualitative tools to validating application designs.
It demonstrated how TR development was beneficial and key in developing consensus among ISA84 members. ISA84 reviewed this standard throughout its development and accepted it as a U. The only modification to IEC for adoption as a U. Today Cost: For new projects, compliance with the IEC safety life cycle typically has minimal impact on total project costs.
It requires project and operations leaders to follow the safety life cycle phases through the design, installation, and operation of the SIS. For existing SIS, the costs to comply will consist of engineering cost and, in most cases, hardware cost. If the PHA has established a tolerable risk for the events under review and determined the target risk reduction for the SIF, little additional engineering is required beyond normal instrument and control design.
If the existing PHA has not adequately defined the need for risk reduction e. The target SIL for the SIF will then be determined to obtain the risk reduction required to obtain the tolerable risk for the event.
Design impact example: If a site chooses to increase the test frequency to meet the target SIL, online testing may be required to avoid frequent process shutdowns. In many cases, at older sites, additional design and equipment will be required to allow online testing.
The increased cost to allow online testing may be offset with the reduced need for future plant shutdowns. In addition, the ability to test the SIFs online removes the need for instrument mechanics on overtime during the plant shutdowns, since testing can be scheduled independent from shutdowns. IEC 1st edition:.
ISA84 approves IEC 61511