What is an arc flash?

An arc flash is a sudden release of electrical energy that occurs when a fault or short circuit causes an arc between two conductors or a conductor and a ground. An arc flash can generate intense heat, light, sound, and pressure that can harm anyone nearby.

How hot can an arc flash get?

An arc flash can reach temperatures of up to 35,000 degrees Fahrenheit, which is hotter than the surface of the sun. This extreme heat can ignite clothing, melt metal, and cause severe burns to the skin and eyes.

The heat from an arc flash can pose a serious risk to a human, even if they are not directly exposed to the arc. The radiant heat can cause second- or third-degree burns to any exposed skin within several feet of the arc. The heat can also ignite flammable materials, such as clothing, hair, or paper, and cause more severe injuries. Furthermore, the intense heat can damage the respiratory system and cause inhalation injuries, especially if there is smoke or toxic gases present. Therefore, it is essential to wear appropriate personal protective equipment (PPE) and avoid working near energized electrical equipment whenever possible.

What is the blast force of an arc flash?

An arc flash can also create a powerful blast wave that can knock workers off their feet, hurl objects across the room, and damage equipment and structures. The blast force can range from a few pounds per square inch (psi) to several thousand psi, depending on the voltage, current, and distance from the arc.

What is the risk to a human from an arc flash?

An arc flash can cause serious injuries and fatalities to workers who are exposed to it. Some of the common effects of an arc flash are:

• Thermal burns: The intense heat from an arc flash can cause deep and painful burns that can damage the skin, muscles, nerves, and organs. Burns can also lead to infections, scarring, and disfigurement.
• Eye injuries: The bright light from an arc flash can cause temporary or permanent blindness, as well as damage to the retina, cornea, and lens. Eye injuries can also impair vision, cause sensitivity to light, and increase the risk of cataracts and glaucoma.
• Hearing loss: The loud noise from an arc flash can rupture the eardrums, damage the inner ear, and cause temporary or permanent hearing loss. Hearing loss can also affect balance, communication, and quality of life.
• Respiratory problems: The smoke and gases from an arc flash can irritate the lungs, throat, and nose, and cause coughing, wheezing, shortness of breath, and asthma. Some of the gases, such as carbon monoxide, can also be toxic and cause poisoning, brain damage, and death.
• Cardiac arrest: The electric shock from an arc flash can stop the heart, cause irregular heartbeat, and damage the heart muscle. Cardiac arrest can also result in brain damage, coma, and death.
• Psychological trauma: The experience of an arc flash can cause post-traumatic stress disorder (PTSD), anxiety, depression, and flashbacks. Psychological trauma can also affect memory, concentration, sleep, and relationships.
• Lung collapse: The blast force from an arc flash can create a shock wave that travels faster than the speed of sound. This shock wave can compress the air in the lungs and cause them to rupture or collapse. This condition is known as pneumothorax. Lung collapse can cause severe breathing difficulties, chest pain, low blood pressure, and cyanosis (bluish skin). Lung collapse can also be life-threatening and require emergency treatment with a chest tube or surgery.

What are calorie limits and why are they important?

A calorie limit is a measure of the amount of heat energy that can cause a second-degree burn on human skin. It is expressed in calories per square centimeter (cal/cm²). A second-degree burn is a burn that damages the outer and inner layers of the skin, causing blisters, pain, and swelling.

Calorie limits are important because they help determine the level of protection that workers need to wear when working near electrical equipment that can cause an arc flash. The level of protection is also known as the arc flash protection boundary (AFPB) or the arc flash hazard boundary (AFHB).

The AFPB or AFHB is the distance from the arc source where the incident energy is equal to or less than a certain calorie limit. The lower the calorie limit, the closer the boundary, and the higher the level of protection required. The higher the calorie limit, the farther the boundary, and the lower the level of protection required.

One of the most widely used calorie limits is 1.2 cal/cm^2, which is based on the National Fire Protection Association (NFPA) 70E standard for electrical safety in the workplace. The NFPA 70E states that workers must wear arc-rated clothing and personal protective equipment (PPE) that can withstand at least 1.2 cal/cm^2 of incident energy when working within the AFPB or AFHB.

How to label electrical equipment for arc flash hazards?

One of the best ways to prevent arc flash injuries and fatalities is to label electrical equipment with information about the arc flash hazards and the required level of protection. Labeling electrical equipment can help workers identify the potential risks, follow the safe work practices, and wear the appropriate PPE.

According to the NFPA 70E, arc flash labels must include the following information:

• Nominal system voltage
• Arc flash boundary
• At least one of the following:
• Available incident energy and the corresponding working distance
• Minimum arc rating of clothing
• Required level of PPE
• Highest hazard/risk category (HRC) for the equipment

Arc flash labels can be created using software, calculators, or tables that estimate the arc flash parameters based on the electrical system characteristics, such as voltage, current, fault clearing time, and equipment configuration. Arc flash labels can also be customized with additional information, such as date, location, and warning signs.

Arc flash labels should be applied to all electrical equipment that is likely to require examination, adjustment, servicing, or maintenance while energized, such as switchboards, panelboards, control panels, meter sockets, and motor control centers. Arc flash labels should be clearly visible, durable, and updated as needed.

How to Calculate Arc Flash Hazards?

To perform an engineering calculation using ETAP or SKM, the following information needs to be collected in the field:

– The type, model, and rating of the electrical equipment and the circuit breakers

– The length, size, and material of the conductors

– The type and location of the transformers and their impedance values

– The source voltage and fault current at the service entrance

– The load characteristics and power factor of the connected devices

Using this information, the software can simulate the electrical system and calculate the incident energy, arc flash boundary, and working distance for each equipment. The software can also generate arc flash labels based on the calculated values.

The requirement to set proper coordination of the circuit breakers is to ensure that the protective devices operate selectively and isolate only the faulty part of the system while maintaining the continuity of service to the rest of the system. Coordination of the circuit breakers can be achieved by adjusting their trip settings, such as long-time, short-time, instantaneous, and ground-fault, according to their time-current curves.

The goal of reducing arc flash times by capturing the arc fault in the instantaneous trip region of the nearest circuit breaker is to minimize the exposure of the workers and the equipment to the hazardous effects of the arc flash, such as high temperature, pressure, sound, and light. Capturing the arc fault in the instantaneous trip region means that the circuit breaker will clear the fault as fast as possible without any intentional delay, thus reducing the duration and magnitude of the arc flash. This can be done by setting the instantaneous trip value of the circuit breaker below the expected arcing current of the equipment.

Another method for estimating the arc flash hazard is to use the tables provided by the NFPA 70E standard, which gives the arc flash boundary and the personal protective equipment (PPE) requirements for various types of electrical equipment based on their nominal voltage, fault current, and clearing time. The tables are intended to simplify the arc flash analysis and provide a conservative estimate of the hazard level.

– The equipment must be properly installed and maintained according to the manufacturer’s specifications and industry standards.

– The equipment must have a bolted fault current within the range specified in the table.

– The circuit breaker must have a total clearing time of 2 cycles or less for voltages below 1 kV, or 6 cycles or less for voltages between 1 kV and 15 kV.

– The circuit breaker must have an instantaneous trip function or an energy-reducing maintenance switching device.

– The equipment must not have any history of arcing faults or incidents.

If any of these conditions are not met, the tables should not be used and a detailed calculation should be done using the methods described in the IEEE 1584 standard. The IEEE 1584 standard provides equations and models to calculate the incident energy and arc flash boundary for different types of equipment, taking into account various factors such as the gap between conductors, the enclosure size, the working distance, and the electrode configuration.

The calculation methods in IEEE 1584 are more accurate and flexible than the tables in NFPA 70E, but they also require more data and expertise to perform. Therefore, it is recommended to use a qualified professional electrical engineer to conduct the arc flash analysis and to verify the results using appropriate software tools.

It is also important to note that both the tables and the calculations are based on assumptions and approximations that may not reflect the actual conditions of the electrical system at the time of an arc flash event. Therefore, the arc flash hazard assessment should be updated periodically (every 5 years at the latest), especially when there are changes in the system configuration, loading, or protection settings. The latest edition of the IEEE 1584 standard, published in 2018, incorporates new research and data on arc flash phenomena and provides revised equations and models to improve the accuracy and validity of the arc flash calculations. It is advisable to use the most current methods and standards to ensure the safety of the workers and the equipment from the arc flash hazards.

What if an arc flash injury has already occurred?

Despite taking all the necessary precautions and following the standards, there is still a possibility of an arc flash incident occurring due to unforeseen or unavoidable circumstances. In such cases, it is essential to act quickly and effectively to minimize the damage and injuries caused by the arc flash. The following steps should be taken if an arc flash injury has already occurred:

– Notify the appropriate authorities and personnel about the incident and cooperate with the investigation and reporting process. Follow the established procedures and protocols for reporting and documenting arc flash incidents in your workplace.

– Contact dreiym engineering as soon as possible for an expert electrical engineer to evaluate the cause and consequences of the arc flash incident, and to provide recommendations and solutions to prevent similar incidents from happening again. Dreiym Engineering is more than just a provider of arc flash analysis and consulting services. They are your trusted partner in ensuring the safety and reliability of your electrical system. With their team of qualified and experienced engineers, they can help you identify and eliminate the potential hazards and risks in your electrical system and provide you with the best practices and solutions to comply with the standards and regulations. Whether you need a comprehensive arc flash study, a detailed incident energy analysis, a customized training program, a forensic analysis of an arc flash event, or a reliable arc flash mitigation system, Dreiym Engineering can deliver the results you need.