Frequently Asked Questions
How can equipment design impact arc flash hazards?
The incident energy exposure caused by an arc flash can be affected by the system configuration, system fault levels, and exposure time. System fault levels can be reduced by changing the system configuration to reduce available fault current, and by using current limiting devices in certain stiuations such as fuses or SST trip devices.
Using faster acting relays and trip devices can reduce arcing time or exposure time. A protective device coordination study should also be conducted to ensure proper device settings. Instantaneous settings could also improve clearing times, limiting the arc exposure time.
Fuse ratings and characteristics should also be evaluated to determine if a smaller and/or faster fuse could be used to help reduce the exposure time.
Why should I have a short circuit and protective device coordination study performed prior to the arc flash hazard analysis?
Arc flash calculations completed in conjunction with short circuit calculations and protective device coordination help ensure that the most accurate arc flash hazard results are achieved. Arc flash hazard boundaries are based on voltage, available short-circuit current and predicted fault duration derived from these analyses.
What data is required to be on Arc Flash Warning Labels?
NFPA 70E 2015 states that compliant arc flash labels shall be field-marked with a label containing all the following information:
- Nominal system voltage
- Arc flash boundary
- At least one of the following:
- Available incident energy and the corresponding working distance, or the arc flash PPE Category, but not both
- Minimum arc rating of clothing
- Site specific level of PPE
Which method of determining flash protection boundary is the best?
All of the known methods have some limitations. The tables provided by NFPA may be easy to use but they are based on typical equipment and systems and are only approximations. They also require information from an up to date short circuit study.
Detailed analysis yields the best results. Therefore, whatever method you use, it is necessary to understand its limitations. Years of industry application experience have resulted in the IEEE1584 standard referenced in NFPA 70E as being the preferred method for a comprehensive arc flash analysis.
How do I determine the flash protection boundary?
The arc flash boundary is based on voltage, available short-circuit current and predicted fault duration. The arc flash boundary can be determined through an arc flash risk assessment that calculates the incident energy level or by using Table 130.7 (C )(16) in NFPA 70E.
What is the Hazard Risk Category?
The hazard/risk category or “HRC” has been changed in NFPA 70E 2015 to “PPE Category.” The categories now range from 1 to 4 where category 1 represents little to no risk and category 4 signifies the greatest risk. PPE categories are not to be used if an arc flash risk assessment has been used to determine the incident energy level. If an arc flash risk assessment has been used to determine the incident energy level, table H3(b) should be used to determine the proper PPE.
What is the difference between NFPA 70E and IEEE 1584 calculations?
NFPA 70E method estimates incident energy based on a theoretical maximum value of power dissipated by arcing faults. This is believed to be generally conservative but is not based on actual test conditions.
In contrast, IEEE 1584 estimates incident energy with empirical equations developed from statistical analysis of measurements taken from numerous laboratory tests.
What data is required for a Short Circuit Analysis?
Typical data that is required for a short circuit analysis includes the equipment type, voltage, AIC rating, available MVA/KVA, impedance, X/R ratio, and multiple electrical properties in the system.
What data is required for an Arc Flash Study?
Depending on the method of calculation, you will need to determine the type of enclosure, gap between exposed conductors, grounding type, available short circuit fault current, electrical properties and working distance.
What is an Arc Flash Study/Analysis?
An engineering study that quantifies the risk of arc flash at each electrical device. Arc Flash Study is used to calculate the incident energy level, which is an indication of how severe an arc flash/blast would be within the device. Once the analysis is complete these values appear on the warning labels placed on the equipment. The labels are then to be used as guide for determining the proper PPE.
What is “incident energy”?
Incident energy is defined in NFPA 70E as, “the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”
How do you determine what PPE is required?
In order to select the proper PPE, incident energy must be known at every point where workers may be required to perform work on energized equipment. These calculations must be performed by a qualified person.
All parts of the body that may become exposed to the arc flash covered by the appropriate type and rating of PPE. Proper PPE can include arc rated clothing, hardhat, hood, face shield, safety glasses, gloves, shoes, etc. depending upon the magnitude of the arc energy.
When is it okay to work on “energized” or “live” equipment?
It is always preferable to work on de-energized equipment. However, OSHA regulations state in 1910.333 (a) that workers should not work on live equipment (greater than 50 volts) except for one of two reasons:
- De-energizing introduces additional or increased hazards such as cutting ventilation to hazardous location, or,
- Infeasible due to equipment design or operational limitations such as when voltage testing is required for diagnostics. When it is necessary to work on energized equipment you should follow safe work practices including assessing the risks, wearing proper PPE, and using the proper tools.
Who enforces these new standards?
OSHA is an enforcer of safety practices in the workplace. OSHA 1910.132(d) and 1926.28(a) states that the employer is responsible to assess the hazards in the work place, select, have, and use the correct PPE, and document the assessment. Though OSHA does not, per se, enforce the NFPA 70E standard, OSHA considers the NFPA standard a recognized industry best practice.
The employer is required to conduct hazard assessment in accordance with 29CFR1910.132 (d) (1).
Employers who conduct the hazard/risk assessment, and select and require their employees to use PPE, as stated in the NFPA 70E standard, are deemed in compliance with the hazard.
Electrical inspectors across the country are now enforcing the new labeling requirements set forth in the 2002 National Electric Code (NEC).
Why are the standards for arc flash changing?
Arc Flash first became an industry concern in the early 1980’s with the publication by Ralph Lee titled, “The Other Electrical Hazard: Electric Arc Blast Burns.” Similar studies illustrated that too many people were suffering injuries as a result of arc flash incidents. Therefore, early adopters in the petrochemical industry took steps to establish the first set of practices designed to better protect employees and electrical contractors.
Soon other industries recognized the need for additional protection against arc flash hazards.These new industry standards developed by the NFPA and others were designed to protect electrical workers from the hazards of shock, electrocution, arc flash, and arc blast.
What standards regulate arc flash hazards?
There are four main regulations governing arc flash. They include:
- OSHA Standards 29-CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E.
- The National Fire Protection Association (NFPA) Standard 70 “The National Electrical Code” (NEC) contains requirements for warning labels
- NFPA 70E provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized.
- The Institute of Electronics and Electrical Engineers (IEEE) 1584 Guide to Performing Arc-Flash Hazard Calculations.
How does an effective preventive maintenance program reduce arc flash hazards?
A preventive maintenance program with respect to overcurrent protective devices is recommended as part of an effective electrical safety program. All arc flash calculations require the arc clearing time in order to determine incident energy and to establish the flash protection boundary. The clearing time is derived from the manufacturers’ time vs. current curves specific to their test standard.
If maintenance and testing is not performed it could result in extended clearing times, unintentional time delays, open or shunted current transformers, open coils or dirty contacts. These factors alone potentially lead to inaccuracy of hazard analysis results. This could also affect the recommendations for the proper PPE.
For this reason, it is recommended that facilities adopt NFPA 70B Recommended Practice for Electrical Equipment Maintenance.
What can I do to reduce my risk to arc flash exposure?
Always perform maintenance in a denergized condition.
Preventive maintenance, worker training, and an effective safety program can significantly reduce arc flash exposure.
As part of a preventive maintenance program, equipment should be thoroughly cleaned and routine inspections should be conducted by qualified personnel who are trained.
Verify that all relays and breakers are set and operate according to manufacturers’ standards.
What is my risk to being exposed to arc flash?
If performing a task involving exposed live equipment, an arc flash is possible.
What can happen if I am exposed to arc flash?
Exposure to an arc flash frequently results in a variety of serious injuries and in some cases death.
Worker injuries can include damaged hearing, eyesight, and severe burns requiring years of skin grafting and rehabilitation. The cost of treatment for the injured worker can exceed $1,000,000.00 per case.
This does not include work in progress loss or job layoffs as a result of the process interruption. These cumulative costs can exceed $10,000,000.
Significant litigation fees, insurance increases, fines, and accident investigation costs can occur.
What is an arcing fault?
An arcing fault is the flow of current through the air between phase conductors or phase conductors and neutral or ground. An arcing fault can release tremendous amounts of concentrated radiant energy at the point of the arcing in a small fraction of a second resulting in extremely high temperatures, a tremendous pressure blast, and shrapnel hurling at high velocity (in excess of 700 miles per hour).
What is a flash hazard?
A flash hazard is defined in NFPA 70E as a dangerous condition associated with the release of energy caused by an electric arc.
Are all arcs equal?
Arcs vary in intensity and duration. The intensity is measured in calories per centimeter squared per second and is dependent on fault current magnitude. The duration of the arc depends on how quickly the protective device interrupts the fault. Intensity and duration must be known to calculate the incident energy to which a worker could be exposed. From this information, the proper personal protective equipment (PPE) can be specified to reduce the exposure.
What causes an Electrical Arc?
Electrical arcs can be initiated by a variety of causes; usually when interacting with the equipment such as testing or when there is moving parts such as turning on a disconnect or starting a motor.
What is the definition of a “qualified” person?
A qualified person is one who has received documented training in the hazards of working on energized equipment in general, and has been trained in the hazards of the particular equipment to be serviced. Training must include the use and proper application of PPE.
What is an “electrically safe work condition”?
An electrically safe work condition is defined as a state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.