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You’d probably agree that your most precious resource is your people. Protecting them should be of utmost importance in both procedure and practice. In the area of electrical systems, a safe workplace begins in the design phase and is maintained throughout implementation, installation, and execution.
Because of the high current and voltage levels associated with these systems, arcing faults release a tremendous amount of energy into the surrounding environment. Think of the resulting flash as an electrical explosion. Arc flashes result from inadvertent contact with energized parts, contamination, and/or equipment failure. The resulting heat and pressure wave cause significant injury, including severe burns and death; and damage equipment within which arcing faults occur.
In addition to having a tremendous impact on injured employees and their families, such events have severe financial consequences for employers and liability insurers. A single serious injury can cost $1 million or more.
Five to 10 arc flashes occur every day in the U.S. Increasing awareness of these dangers has brought more attention to safety standards. Years of research led to increasingly stringent regulations beginning in the late 1990s.
Most attention, however, focuses on system analysis and personal protective equipment (PPE), rather than on products or design solutions that reduce hazard levels or mitigate risk. Moreover, municipal water and wastewater operations don’t fall under OSHA enforcement, and only 27 states have OSHA-approved programs that exercise jurisdiction over public-sector employers and employees.
Ideally, employees shouldn’t work on energized electrical equipment. But because some diagnostic and repair tasks require it, employers must find and implement ways to reduce arc flash potential. Mitigation equipment and techniques can be applied, but they’re just one step to a safer workplace. Any mitigation solution must be informed by, and integral to, a facility’s work practices.
Don’t rely solely on PPE
While PPE, administrative controls, and warnings are required for every facility and make up essential parts of electrical safety policies and practices, they are the least effective mitigation solutions. PPE, in particular, is often mistakenly viewed as the solution to arc flash hazards. Some believe that if a worker wears a flash suit (adequately rated or not) he or she is equipped to work anywhere, anytime.
As the primary industry consensus standard, “Standard for Electrical Safety in the Workplace” (NFPA-70E02012), contains extensive information on safe work practices, analysis procedures, requirements for documentation and equipment labeling, and PPE selection principles. But even properly selected PPE doesn’t guarantee freedom from injury. The NFPA 70E standard only claims that injuries would be “reduced” and “survivable.”
That’s why effective safety programs also incorporate “safety by design” and other mitigation solutions.
Engineering less risk
Obviously, completely eliminating a hazard is most effective. When that’s not feasible, many facilities implement engineering controls that mitigate the hazard.
Although not as effective as substitution or elimination, engineering controls are more effective than PPE because they seek to reduce the degree of hazard. And because they don’t rely solely on the employee to follow safety policy and procedures, they’re also considered more effective than administrative controls and warnings.
Engineering controls can be broken into these categories:
1. Avoidance: Staying a safe distance away from the potential arc; protects employee but not equipment. Examples:
- viewing windows that allow thermal scanning of equipment without exposing live parts;
- remote monitoring and control solutions that communicate a device’s state without employees entering the electrical room;
- insulated bus (including the bus joints) for shock protection.
2. Passive containment: Arc-resistant equipment is designed to withstand the effects of an internal arcing fault and to redirect gasses and particles away from employees close by. Instead of reducing duration or energy, it contains energy via doors and covers before redirecting and safely venting.
Employees are unprotected during maintenance or any time the doors are open or covers removed. Due to installation and venting requirements, retrofitting usually isn’t an option.
3. Passive protective devices: Devices, schemes, and settings are selected so that their response to arcing fault currents, while no different than to other faults, is fast enough to satisfactorily reduce energy levels.
4. Active protective devices: Techniques that clear (or quench) faults very quickly, typically in less than a few cycles, using sensing techniques that differentiate between arc flash and other fault types.
5. Interactive protection: Employee initiates protective device clearing.
The use of any one of these controls, or a combination of two or more, depends on the number of application-specific situations unique to each circumstance.