Mitigation vs. Prevention
Terminal and pipeline facilities in the oil and gas industry are often susceptible to arc flash hazards. Most of these projects in the U.S. still follow a mitigation strategy, says Tim Howd, a senior electrical and instrumentation engineer at Burns & McDonnell. The emphasis is on reducing the severity of arc flash incidents when they occur, and it often is considered only at the end of a project. By comparison, engineers in the U.K. focus on preventing arc flash incidents through the use of the hierarchy of controls.
Mitigation strategies in the U.S. are built around lower-order controls, like safe work practices and the use of personal protective equipment (PPE). Preventive strategies use higher-order controls, such as isolating people from the hazard, replacing the hazard with a less dangerous alternative or physically removing the hazard.
“For lower-order controls to work, individual supervisors and workers must implement them correctly and consistently. But humans are prone to making mistakes,” Howd says. “Higher-order controls are far better for reducing overall risk because they don’t require human intervention and they aim to prevent arc flash incidents entirely.”
Prevention by Design
To be most effective, arc flash prevention needs to be addressed and engineered during the design phase of every terminal and pipeline project.
“It’s not always the easiest thing to do, because you have to be intimately familiar with how different variables will impact the results before the incident energy calculations are made,” Howd says. “But an experienced electrical engineer can provide very accurate estimations by using sound judgement to determine ranges the variables are likely to fall within.”
Evaluating arc flash hazards early allows engineers to build in multiple layers of protection using the hierarchy of controls. Some layers are designed for mitigation. For example, in the event of an arc flash, arc-resistant equipment contains most of the energy and redirects it to a safe location.
Other layers — like active arc flash detection, neutral grounding resistors, arc quenching devices and even preventive maintenance — are more often overlooked, but are critical in preventing electrical system incidents.
Source: ANSI Z10: Occupational Health and Management
Shift to Higher-Order Controls
Safety management professionals have encouraged the application of higher-order controls to reduce electrical hazards since “ANSI Z10: Occupational Health and Safety Management Systems” was published in 2005. Adoption of this approach has been inconsistent. But with publication of the 2018 edition of “NFPA 70E: Standard for Electrical Safety in the Workplace,” which added sections referencing ANSI Z10 and the hierarchy of controls, this is beginning to change.
“As the focus shifts from mitigation to prevention, the application of higher-order controls — like engineering controls, substitution and elimination — will allow terminal and pipeline companies to optimize for safety,” Howd says. “The earlier these preventive concepts are introduced into the project life cycle, the more effective they will be from both a safety and cost perspective.”
To learn more about using the hierarchy of controls to prevent arc flash hazards, check out a recently completed white paper here.