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October 05, 2019
There are additional steps companies can take to mitigate arc flash hazards and remove workers from harm’s way
An arc flash is defined as a hazardous explosion of energy from an electrical circuit, or a type of discharge that results 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 Fahrenheit, arc flash incidents can also damage equipment and interrupt business operations, leading to significant 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 Protection 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 policy, conduct an arc flash risk assessment to evaluate the likelihood of occurrence and severity of arc flash hazards, follow strategies to mitigate and control arc flash hazards, conduct regularly scheduled safety training and audits for all electrical workers, maintain electrical distribution system components and ensure adequate 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 amount of arc flash energy reduction will be determined 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 design” approach into switchgear, even if the system is decades old. For example, digital relays with overcurrent 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 detecting 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 challenging 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, maintenance, 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 construction like exhaust plenums?
The answers to these questions will shape the system design.
Consider these recommendations while selecting arc flash mitigation techniques: reduce AFIE (Arc Fault Incident Energy) level, or PPE, as much as possible, improve service continuity, reduce exposure to live parts, simplify commissioning and usage to reduce human risk factor, optimize cost for Capex and Opex and save space with the minimum footprint and less construction.
Within electrical equipment, the arc flash risk can vary dramatically, and this typically results in a maximum “zone” of risk associated with the line-side of the main circuit breaker. Another zone of risk, typically an order of magnitude less, exists on the load side of the main circuit breaker. The question is, what is the sufficient isolation in between line side and load side of an electrical enclosure?
A risk assessment should include evaluating the incident energy in each of these zones and creating an understanding of proximity risk, that is, what is the chance that an arc, created downstream of the main circuit breaker, could transfer to the line-side of the main circuit breaker? Serious consequences would result if this were to happen and the worker was wearing PPE appropriate only for the load side risk or vice versa.
An arc flash is defined as a hazardous explosion of energy from an electrical circuit, or a type of discharge that results 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 Fahrenheit, arc flash incidents can also damage equipment and interrupt business operations, leading to significant 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 Protection 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 policy, conduct an arc flash risk assessment to evaluate the likelihood of occurrence and severity of arc flash hazards, follow strategies to mitigate and control arc flash hazards, conduct regularly scheduled safety training and audits for all electrical workers, maintain electrical distribution system components and ensure adequate 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.
Safety by Design
The amount of arc flash energy reduction will be determined 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 design” approach into switchgear, even if the system is decades old. For example, digital relays with overcurrent 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 detecting 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 challenging 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, maintenance, 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 construction like exhaust plenums?
The answers to these questions will shape the system design.
Consider these recommendations while selecting arc flash mitigation techniques: reduce AFIE (Arc Fault Incident Energy) level, or PPE, as much as possible, improve service continuity, reduce exposure to live parts, simplify commissioning and usage to reduce human risk factor, optimize cost for Capex and Opex and save space with the minimum footprint and less construction.
Arc Flash Assessments
Within electrical equipment, the arc flash risk can vary dramatically, and this typically results in a maximum “zone” of risk associated with the line-side of the main circuit breaker. Another zone of risk, typically an order of magnitude less, exists on the load side of the main circuit breaker. The question is, what is the sufficient isolation in between line side and load side of an electrical enclosure?
A risk assessment should include evaluating the incident energy in each of these zones and creating an understanding of proximity risk, that is, what is the chance that an arc, created downstream of the main circuit breaker, could transfer to the line-side of the main circuit breaker? Serious consequences would result if this were to happen and the worker was wearing PPE appropriate only for the load side risk or vice versa.
SOURCE:
https://ohsonline.com/Articles/2019/10/01/Protecting-Against-Arc-Flash-with-Safety-by-Design.aspx?Page=1
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