Page 50 - Occupational Health & Safety, October 2019

ELECTRICAL SAFETY
Protecting Against Arc Flash with “Safety by Design”
There are additional steps companies can take to mitigate arc flash hazards and remove workers from harm’s way. BY ERHAN COKAL
An arc flash is defined as a hazardous ex- plosion of energy from an electrical circuit, or a type of discharge that re- sults from a low-impedance connection through air to ground or to another voltage phase in an electrical system.
In the United States, arc flashes occur as often as five to 10 times per day. Many of these incidents result in injuries, and some are even deadly.
Creating a heat blast of up to 35,000 degrees Fahr- enheit, arc flash incidents can also damage equipment and interrupt business operations, leading to signifi- cant economic losses. The cause can be as simple as a rodent, a misplaced tool, humidity issues, or another element in the breaker area that compromises the electrical “spacing” between energized components. Essentially all electrical systems of voltages 200V or greater are susceptible to arc flash incidents.
To protect electrical systems from these disastrous effects, electrical professionals must comply with OSHA enforced electrical safety standards in their state and local jurisdiction. The National Fire Protec- tion Association’s NFPA 70E1, Standard for Electrical Safety in the Workplace, outlines a six-step process for the proper design and installation of electrical systems: develop and audit electrical safe work practices poli- cy, conduct an arc flash risk assessment to evaluate the likelihood of occurrence and severity of arc flash haz- ards, follow strategies to mitigate and control arc flash hazards, conduct regularly scheduled safety training and audits for all electrical workers, maintain electri- cal distribution system components and ensure ad- equate supply of personal protective equipment (PPE) and proper tools that act as the “last line of defense” for exposed workers.
However, there are additional steps companies can take. Incorporating a “safety by design” approach through the engineering controls helps mitigate arc flash hazards by significantly reducing the arc flash energy levels and removing workers from harm’s way.
The Figure 1 illustrates the six types of risk control methods arranged in order of effectiveness. At the top of the list is “Elimination”—in other words, discon- necting the circuit from the source, LOTO, and veri- fying the absence of voltage.
The Engineering Controls option reduces risk without worker involvement (for example, GFCI pro- tection, or barriers). The Elimination, Substitution and Engineering Controls are usually applied at the source and are less likely to be affected by human er-
ror. The line side isolation solution has focused engi- neering controls in conjunction with other methods to lower the overall risk level. The final line of defense is PPE (Personal Protection Equipment). It needs to be properly rated for the hazard, whether it is shock or arc flash or both.
Figure 1. Risk Control Methods
Safety by Design
The amount of arc flash energy reduction will be deter- mined by an engineering analyses, which will always be a function of the upstream circuit breaker or fuse. This is because arcing time is the key determining factor for arc flash energy. Since incident energy is proportional to arcing time, the use of a faster-acting devices is key. As a result, proper selection of overcurrent protective devices and systems—in particular, selecting control devices that will quickly clear arcing faults from the power system—is a powerful mitigation strategy.
There are choices for retrofitting a “safety by de- sign” approach into switchgear, even if the system is decades old. For example, digital relays with overcur- rent sensing can now be added to the low-voltage side of a service transformer designed to trip an existing upstream device. Or, light sensors capable of detect- ing arcs in just a millisecond can be installed within switchgear compartments. A comprehensive look at the system through a safety lens can identify the right options for almost any installation.
Selecting an arc flash mitigation method is a chal- lenging task for many facilities. A simple, reliable and affordable design is expected. In order to achieve this challenging task, here are a few critical questions to ask in the early stage of the system design:
1. How can I reduce the hazard risk?
2. What is my PPE goal?
3. Which operations do I need a PPE, mainte-
nance, troubleshooting?
4. Is service continuity or equipment damage a
concern for my system and process?
5. What is my budget to achieve the goal?
6. What is the restriction for additional construc-
tion like exhaust plenums?
46 Occupational Health & Safety | OCTOBER 2019
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