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Instilling process safety standards into a firm’s core values isn’t easy, says Rick Dunn, consultant and senior project engineer in DuPont’s engineering division in Wilmington, Del. “Companies exist to make money, but more are recognizing that safety can pay for itself, and that a lack of safety can make their profit and revenues vanish,” he says. “S84 has been implemented into DuPont’s internal standards because we recognize that process safety pays.”
Process safety technologies are evolving as rapidly as plant-floor applications and the standards that cover them.
Traditional process safety manufacturers, such as HIMA, Triconex and ICS Triplex, have been making redundant systems for many years. However, they’ve recently been joined by several dozen control system manufacturers, who report that safety and control devices can be more closely integrated, while their functions remain separate. Supporters of integrated SISs report that using multiple microprocessors gives their solutions enough computing power to do constant monitoring, test applications more frequently, conduct more internal diagnostics, trigger fewer nuisance trips and perform safe shutdown operations when needed.
“The old concept that a PLC can perform both BPCS and SIS has been repackaged by the vendors and given credibility by certification,” adds Summers. “This isn’t a new concept. The only thing that’s new is the ability to get it certified. This wasn’t allowed in previous process sector SIS standards, but is allowed in IEC 61508, since it covers other sectors, such as transportation, and medical, as well as manufacturing.”
Of course, any PLC with digital and analog I/O and appropriate algorithms can do both,” Summers continues. “The problem is that most process industry users don’t rigorously document, validate, control access to or manage changes to their control system. This is required when control systems and safety instrumented systems are combined.”
Dunn reports that users are implementing SISs in more new projects to see if they improve safety and integrate better with controls systems. “Certification helps, but there are many folks who don’t understand what this means,” says Dunn. “It’s still buyer beware out there. The end user is still responsible for the safety of his operation.”
Adler adds that, “Whatever SIS you pick, you must still look at the entire loop from the field to the control and back. You can install the best safety PLC ever, but if it’s applied improperly by relying on old transmitters and valves with bad measurements, then you haven’t accomplished anything.”
To-Do List for Safety
Despite the limitations of present standards and certifications and the variable applications where process safety is needed, there are some basic procedures that all must follow to implement it. Most versions of this laundry list are based on OSHA’s 1910.119 process safety management (PSM) of highly hazardous chemicals regulations (see sidebar), which tells users to perform a process hazard analysis (PHA).
To identify use and application trends of safety instrumented systems (SIS) among process automation professionals, Control conducted an electronic survey of 114 readers in February 2007. Key findings of the survey include:
U.S. Occupational Safety and Health Administration’s guidelines for complying with its 1910.119 process safety management (PSM) of highly hazardous chemicals regulations are the foundation for many individual PSM plans. Expanded versions of these rules are available online at www.osha.gov. In short, these guidelines instruct users to:
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