Revised Functional Safety Starts Now

Wednesday, January 25, 2012 @ 04:01 PM gHale


By Nicholas Sheble
“Sixty six percent of your safety systems are between 11- and 30-years-old. Indeed, many are from the days of the DCS (distributed control system) and relay-based control systems,” said ABB’s Luis Durán.

Durán, a certified functional safety engineer and is product-marketing manager — safety for BU Control Technologies for ABB, Inc., conducted a webinar Tuesday entitled “Is Your Safety System Compliant? Find Out and Plan Your Next Steps.”

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Durán also said a new edition of IEC 61508 takes effect this month. IEC 61508 is “Functional Safety of Electrical/Electronic/Programmable Electronic (E/E/PE) Safety-related Systems.”

The standard is applicable to all kinds of industries defining functional safety as “part of the overall safety relating to the EUC (Equipment under Control) and the EUC control system which depends on the correct functioning of the E/E/PE safety-related systems, other technology safety-related systems, and external risk reduction facilities.”

Functional safety relies on active systems. For instance:
• The detection of smoke by sensors and the ensuing intelligent activation of a fire suppression system is an example of an active system and functional safety.
• As well, the activation of a level switch in a tank containing a flammable liquid, when a potentially dangerous level has been reached, which causes a valve to close to prevent further liquid entering the tank and thereby preventing the liquid in the tank from overflowing is another example.

Safety achieved by measures that rely on passive systems is not functional safety.

Durán said safety automation infrastructure might very well have gone into service while today’s safety standards including IEC 61508 and IEC 61511/ISA 84 were still in development.

“Some of these safety systems, particularly the ones installed between the late 1980’s and early 2000, are either general-purpose PLCs, or are not designed as a safety system according to the IEC 61508 standard,” Durán said.

Other systems might not satisfy current requirements with IEC 61508 and overall they don’t comply with IEC 61511, which is the standard that sets out practices in the engineering of systems that ensure the safety of an industrial process using instrumentation – Safety Instrumented Systems (SIS).

The standard is “Functional safety – Safety instrumented systems for the process industry sector” and it is fully incorporated in ISA84 and applicable to manufacturing processes like refineries, petrochemical, chemical, pharmaceutical, pulp and paper, and power.

Durán didn’t cover all the changes to 61508 but did note the new approach to the management of functional safety, which provides for more comprehensive normative requirements:
• Appointment of one or more persons by an organization with responsibility for one or more phases necessary for the achievement of functional safety of an E/E/PE safety-related system;
• Identification of all persons undertaking defined activities relevant to the achievement of functional safety of an E/E/PE safety-related system;
• All those persons undertaking defined activities relevant to the achievement of functional safety of an E/E/PE safety-related system shall be competent for the duties they have to perform.

To see all the changes in IEC 61508 click on this International Electrotechnical Commission link.

Nicholas Sheble (nsheble@isssource.com) is an engineering writer and technical editor in Raleigh, NC.



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