Standards and regulations may change, but the danger associated with arc flash hazards remains. Analyzing potential incident energy correctly and understanding what personal protection equipment is required can help workers stay safe and avoid painful, or even life-threatening, injuries.
The Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA) have both established new requirements for protecting workers from the hazard of electric arc flash. Many people have difficulty interpreting these new rules, however. Some people will read through the Federal Register and/or NFPA 70E: “Standard for Electrical Safety in the Workplace” and come away with a good understanding of the new requirements. Others will skim over the material in hopes of picking out the “important” parts, while many people will not even try to read the documents.
People in the first group probably don’t need to go any further; if you’re the type of person to read through the Federal Register or a standard, you’ve probably already got the information you need. This article is for the other two groups, who probably make up 80% of the workforce that needs the information but either doesn’t have time to read things in detail or doesn’t have the patience to slog through the information.
One thing to remember is that NFPA 70E and OSHA regulations are minimum acceptable requirements, not best work practices. Workers are expected to meet or exceed the requirements set forth in NFPA 70E and OSHA 1910.269, 1910.331 through 1910.335, and 1926 Subpart V. Those of us who try to avoid visits to the emergency room regularly exceed those minimum requirements.
New OSHA Requirements
There used to be significant differences between OSHA’s 1910.269 and 1926 Subpart V regulations. However, OSHA determined that the hazards and risks covered by the two regulations were very similar, so consistency was needed between them to reduce confusion and simplify their use.
1910.269 covers electric power generation, transmission, and distribution, while 1926 Subpart V covers construction activities on overhead power lines. Changes made to 1910.269 apply to 1926 Subpart V and vice versa. Users of the 1910.269 regulation will find mostly minor changes, except for portions covering information transfer, protecting employees from arc flash hazards, and fall protection. This article looks at the new requirements for protecting workers from the arc flash hazard.
One of the new requirements—1910.269(l)(8)(iii)—is that employers must ensure workers who are exposed to an arc flash hazard do not wear clothing that could melt into their skin if they are exposed to an electrical arc. This requirement was effective immediately upon release, although OSHA stated that the existing requirements in 1910.269 would be acceptable until April 1, 2015. (By the way, the old regulation required pretty much the same thing.)
Companies covered by these regulations were required by January 1, 2015, to assess the workplace to identify employees exposed to the hazard of electric arcs and make a “reasonable” estimate of incident energy to which their employees may be exposed. If you read the preamble and supporting material, OSHA went to great lengths to explain what “reasonable” meant. It compared four methods of estimating incident energy and indicated where these methods could or could not be used. Note 1 in 1910.269(l)(8)(ii) directs the user to Appendix E (Table 1) for more guidance on assessing arc flash hazards, and selecting arc-rated clothing and personal protective equipment (PPE).
|Table 1. Selecting a reasonable incident-energy calculation method. This table is from 1910.269 Occupational Safety and Health Standards Appendix E. Source: Occupational Safety and Health Administration (OSHA)
Note that some methods are considered reasonable for under 600-V exposures, some are reasonable for up to 15-kV exposures, but only one method—Arc Pro—was found by OSHA to provide reasonable estimates when the voltage is above 15 kV. For OSHA to specify a commercial product is very unusual, but the other available methods were never intended for use above 15 kV, except for Ralph Lee’s equations, but he had limited resources to develop them, and OSHA considers his equations to be too conservative. The Lee method and the Doughty, Neal, and Floyd methods are not generally used, as the Institute of Electrical and Electronics Engineers (IEEE) standard 1584 superseded them.
There is another software-based model available called “Flux.exe,” which uses equations developed by Duke Energy. This is an older program that does not run in newer versions of Windows, but was designed to calculate the incident energy (heat flux) generated by a single-phase overhead power line, much like Arc Pro does. OSHA states that it is willing to consider other methods companies may want to use for calculating incident energy, if the estimates are reasonable. According to OSHA, each task does not have to be analyzed, and companies can make broad estimates, but I think any company desiring to use a different methodology should get OSHA approval first.
The first new requirement—1910.269(l)(8)(vi)—that went into effect on April 1, 2015, is that the outermost layer of clothing must be arc-rated if any of the following four conditions are met:
■ The employee could contact energized conductors or circuit parts rated greater than 600 V.
■ An electric arc could ignite flammable material in the work area that could also ignite the worker’s clothing.
■ Molten metal from an electric arc could ignite the employee’s clothing.
■ The incident energy exceeds 2.0 cal/cm2.
The requirement applies to rainwear, parkas, jackets, safety vests, fall-arrest harnesses, or any other clothing worn as the outer layer. Arc-rated clothing is not designed or rated to resist heat for substantial periods of time. Although the incident energy from an arc flash can be very high, the time of exposure is short—usually less than six cycles (0.10 second). Meltable, or ignitable, clothing or materials worn on top of arc-rated clothing can cause it to fail.
The worker must wear arc-rated clothing when the incident energy exposure is estimated to be above 2.0 cal/cm2. The arc-rated clothing and PPE selected must have a rating equal to or greater than the estimated incident energy. This arc-rated clothing and PPE must cover all parts of the worker’s body, except for hands and feet, which have their own requirements (covered later in this article).
A 2-cal/cm2 exposure on bare skin would cause a more serious injury than one at 1.2 cal/cm2, but the latter is still within the lesser second-degree burn injury category. As a point of reference, 5.0 cal/cm2 produces wide-area second-degree burns, while approximately 8 cal/cm2 results in a third-degree burn (all at six cycles or 0.10 second). OSHA notes in Appendix E that it expects cotton clothing to reduce the heat received to the body to 1.2 cal/cm2 or less when incident energy is 2 cal/cm2.
Conversely, the 70E committee rejected using cotton clothing as a form of arc-protective clothing, as cotton will ignite and burn vigorously at some value of incident energy. Given the fact that arcs in field conditions are somewhat unpredictable, we felt it was the proper thing to do. (I served on this panel.) Even though the 2.0 cal/cm2 threshold seems reasonable at first glance, the end result of an arc flash event may not necessarily be the 2.0 cal/cm2 that was estimated.
All calculations of this type, regardless of methodology or software package, are estimates based on fixed values. Most people associated with the electric power industry know that the power system is not static, and there are a host of variables that cannot always be accounted for. At least in industrial facilities being fed by a power transformer, its impedance will help dampen surges and transients somewhat, along with the capacitor banks that are often installed.
I advise workers covered by 1910.269 and 1926 Subpart V to consider the consequences of receiving a second-degree burn versus the onset of a second-degree burn. It may seem like a small difference, but with the onset of a second-degree burn, the skin is not uniformly blistered, and chances of infection are relatively small. As incident energy increases above the onset of second-degree burn threshold, the blistered area will be larger. Blistering from burns greatly increase the risk of infection, and with antibiotic-resistant germs cropping up in some medical facilities, survival chances are not nearly as good.
A worker’s hands must be protected from an electrical arc, and OSHA notes that wearing rubber insulating gloves and leather protectors is adequate protection. If the worker is wearing heavy-duty leather gloves, they are considered adequate up to about 14-cal/cm2 incident-energy exposure.
W.H. Salisbury & Co., now Salisbury by Honeywell, conducted an arc study on rubber insulating gloves and leather protectors. It found that the combination provided a very good level of protection from the heat of an electric arc. At a recent American Society for Testing and Materials (ASTM) F18 committee meeting, several utilities stated that they had never had a worker’s hands injured from an electric arc when wearing rubber insulating gloves and leather protectors. If the worker is wearing heavy-duty leather work shoes, no additional arc flash protection is needed for the feet.
The section of the regulation addressing head and face protection almost reads like something out of The Twilight Zone series—it just needs Rod Serling to narrate. 1910.269(l)(8)(C) states that arc-rated protection is not needed for the head for single-phase open-air arcs up to 9 cal/cm2 (5 cal/cm2 for multi-phase) if the worker is wearing head protection meeting 1910.135 requirements, which includes the use of a voltage-rated hard hat if the worker could contact energized conductors or circuit parts.
A minimum 8-cal/cm2 arc-rated face shield is required to protect the face with a hard hat up to an incident-energy exposure of 13-cal/cm2 single-phase open-air, or 9-cal/cm2 for multi-phase, exposures. OSHA goes on to state that for single-phase exposures in open air, the arc rating of the clothing and PPE can be 4 cal/cm2 less than what is estimated. Table 2 is from 1910.269 Appendix E and provides a summary of the requirements for arc-rated face protection. OSHA regulations (and NFPA 70E) are minimum requirements and, as stated earlier, workers should strive to exceed them.
|Table 2. Arc-rated head and face protection. This table is from 1910.269 Occupational Safety and Health Standards Appendix E. Source: OSHA
I’m not the sharpest pencil in the box, but these numbers just don’t seem to be reasonable. It is widely known that 8 cal/cm2 received on bare skin for 0.1 second results in a third-degree burn. I can’t understand why OSHA, or the utility industry, would believe it is acceptable for workers to be at risk of a third-degree burn. I realize utilities use a lot of current-limiting fuses, reducing fault-clearing time. I also realize that incident energy dissipates more rapidly in open air than in an enclosure. However, incident energy is calculated to the face and chest area, and 9 cal/cm2 incident-energy exposure is still 9 cal/cm2 incident-energy exposure—I don’t care if it is industrial electricity or utility electricity. If anything occurs that increases fault-clearing time even a smidge, a worker could receive disabling, and possibly life-threatening, injuries. Maybe the utility industry got its way on this, but it did its employees who are at risk a disservice, in my opinion. I advise anyone who is exposed to the risk of an electric arc flash to wear protective equipment rated for the estimated incident energy calculated.
NFPA 70E Table Method
In the 2015 edition of NFPA 70E, the table method received its first real makeover since the 2000 edition. Each prior cycle, proposals were submitted stating that the table method did not adequately protect workers who used it. Even though the 70E committee did not receive a validated example of a serious injury if a worker followed all of the table method requirements, there was cause for concern.
The old table method would reduce the hazard/risk category (HRC) number by 1, 2, or 3 numbers based solely on the perceived risk of a task. The potential was there for someone wearing a reduced HRC PPE to be involved in an arc flash and receive serious burns. Another problem was that many people just did not understand it. They found the table method cumbersome and complex.
To the 70E committee, the problem was much like taking an ugly date to the prom; once you’re there, you’re pretty much stuck with your choice. The 70E committee fielded numerous proposals to make changes over several cycles, but there were no good alternatives—that is, until the 2015 cycle.
As we were once again discussing the pros and cons of the table method, David Wallis, former director of OSHA’s Office of Engineering Safety and primary author of many OSHA electrical standards, including 1910.269 and 1926 Subpart V, said, “Why don’t you do it the way OSHA looks at whether an arc flash hazard exists?” David laid out a methodology that first determined if an arc flash hazard existed and then what to wear for PPE.
I have to admit, I was not a fan at first, but it did seem to work, and it corrected the shortcomings of the table method that everyone loved to hate. The 70E committee was unwilling to state that no arc flash hazard existed, but members eventually agreed on the wording “No Arc Flash PPE Required.” Personally, I would have preferred that it read “No Arc Flash PPE Mandated,” because it may be required, but the standard just can’t make that judgment call.
Is PPE Required?
Table 3 shows a portion of Table 130.7(C)(15)(A)(a) from NFPA 70E. Referring to the table is the first step when using the new table method. If all the conditions in the table are met, no arc-rated clothing or PPE is required in many cases. However, if any of the conditions are not met, arc-rated clothing and PPE are required. Some tasks, such as voltage testing or racking of circuit breakers, always require arc-rated clothing and PPE, but the new table method gives the worker some flexibility.
I chose the example task in Table 3 because it was one that created a lot of discussion among committee members. A small group did not like the new table method. One person stated, “It was like going back to the 1950s.” The crux of the disagreement was whether NFPA 70E provided minimum work practice requirements or best work practice requirements. The majority of committee members believe the standard presents the minimum acceptable requirements and encourages workers to exceed those minimum requirements.
As such, NFPA 70E should provide guidance but should not be used as a “crystal ball” for every possible circumstance or situation. To this end, we added a note at the bottom of Table 130.7(C)(15)(A)(a), which states, “The assessment of the likelihood of occurrence contained in this table does not cover every possible condition or situation.” We can’t see what workers see, so workers must make a judgment call as to the applicability of the table to their current situation and circumstances.
An example is the task of normal operation of a circuit breaker. At less than 600 V, if all of the conditions are met in Table 130.7(C)(15)(A)(a) and its continuous current rating is less than 600 A, I’d agree that no arc-rated clothing or PPE is mandated. However, for circuit breakers that have a larger continuous current rating, medium-voltage circuit breakers or switches, or if I get a gut feeling that something is not right, even though I can’t put my finger on it, I would wear at least PPE category 2 arc-rated clothing and gear.
The note also states, “Where this table indicates that arc flash PPE is not required, an arc flash is not likely to occur.” The phrase “not likely” doesn’t mean “not ever,” “not possible,” or “won’t.” It does mean that, if all conditions noted in the table are met, the chances of an arc flash are pretty small. “Pretty small” does not equal zero. Workers must use their best judgment when using the table method and be certain to understand the condition of maintenance of the equipment they are about to work on. The OSHA regulations include a similar table (Table 4) for use in evaluating tasks.
|Table 4. Example assessments for various tasks. Note the similarities between this partial table from 1910.269 Appendix E Table 1 and the partial table from NFPA 70E Table 130.7(C)(15)(A)(a), shown in Table 3. Source: OSHA
The second step in the table method is to refer to Table 130.7(C)(15)(A)(b) (Table 5) and choose the type of equipment about to be worked on. Each category of equipment has limits for the available short circuit current and the fault-clearing time. As an example, the equipment category “Panelboards or other equipment rated >240 V and up to 600 V” has limits of 25 kA available short circuit current and 0.03 second (2 cycles) fault-clearing time. If either of these two limits is exceeded, an incident-energy analysis must be performed.
This table also provides the estimated working distance and arc flash boundary. The working distance should always be considered when exposed to arc flash hazards. If the worker’s body position is closer than the given working distance, incident energy will be greater than what is estimated for the table method, and the chances of a burn increase. Incident energy increases rapidly as the distance decreases.
For example, using the IEEE-1584 spreadsheet to evaluate a 600 V-class molded-case circuit breaker operating at 480 V and 2 cycles (0.03 second) clearing time with a working distance of 24 inches and short circuit available current of 25 kA, the potential incident energy received by a worker on his chest and facial area would be 4.14 cal/cm2. If the distance is reduced to 18 inches (keeping all other conditions the same), the incident energy increases to 7.13 cal/cm2. That’s a big increase over a short distance! This is a fairly low-energy example, but the concept applies for all variations in distance.
If using the 70E Table Method and the working distance is not 18 inches, an incident-energy analysis is required. In the example shown in Table 5, PPE category 2 arc-rated clothing and gear is indicated, with an arc flash boundary of 3 feet. The arc flash boundaries were rounded up to the nearest foot, with the exception of PPE category 1, which was left in inches. This was to simplify the table as much as possible.
Are You Really Protected?
The last step in the table method is to refer to Table 130.7(C)(16). In the example in Table 5, PPE category 2 arc-rated clothing and gear are required. Table 130.7(C)(16) provides the arc-rated and non-arc-rated PPE required for each PPE category. Table 6 shows PPE category 2 requirements from Table 130.7(C)(16). All parts of the equipment listed must be worn as required by the manufacturer in order to provide the level of protection specified. Refer to NFPA 70E 130.7(C) for protective equipment clothing and PPE requirements.
|Table 6. PPE category 2 requirements. All parts of the equipment listed must be worn in accordance with the manufacturer’s instructions in order to provide the protection specified. Source: NFPA 70E
The new table method requires a qualified person to be able to make a determination of whether the equipment has been properly installed, properly maintained, and if there is evidence of impending failure.
Determining if equipment is “properly installed” is relatively easy. If the electrical equipment was installed in accordance with the manufacturer’s instructions, codes and standards, and inspected and approved by the authority having jurisdiction, normally the installation is considered to be properly installed. However, there may be defects that were not detected at the time of installation that could cause failure at a later date.
Whether equipment is “properly maintained” is more difficult to determine. Workers at a single job site should have a good understanding of the condition of maintenance, but technicians coming in as contractors may not. NFPA 70E references NFPA 70B “Recommended Practice for Electrical Equipment Maintenance” in several informational notes. NFPA 70B section 11.27 “Test or Calibration Decal System” provides a method for determining the condition of maintenance and is a system many InterNational Electrical Testing Association (NETA)-member companies use to assist their customers in tracking and maintaining their electrical equipment.
NFPA 70B 11.27 uses a three-decal classification system to denote condition of maintenance (Figure 1). Each decal has a test or maintenance date, the company that performed the tests, and one of three colors: white, yellow, or red. A white decal is attached to the device or equipment if it has passed all inspections and tests. A yellow decal indicates the device or equipment had a minor defect that does not affect its operation or safety. A red decal indicates the device or equipment has a more serious problem that should be corrected before reinstallation or as soon as possible. For more information on the test or calibration decal system, please refer to NFPA 70B 11.27.
|1. Test or calibration decals. Following a classification system outlined in NFPA 70B section 11.27, colored decals make maintenance condition more readily apparent. Courtesy: Shermco Industries Inc.
The decals only represent the condition of maintenance on the date the maintenance or testing was performed. As time passes, the condition of maintenance could, and probably will, change. NFPA 70B and American National Standards Institute (ANSI)/NETA maintenance testing specifications both generally recommend a three-year maintenance cycle, which could be extended or reduced, depending on several factors. Consult a NETA-member company in your area for specific recommendations for your power system.
Finally, “evidence of impending failure” requires a qualified person to have an understanding of the possible defects of electrical equipment and devices and their symptoms. Insulation that is failing may produce ozone, which has a peculiar and unique odor. If someone has not smelled ozone previously, they may not recognize it as a possible indication of impending failure. Bringing in an expert to evaluate equipment is one way to reduce the likelihood of problems going unnoticed until a failure results. ■
—James R. White ([email protected]) is training director for Shermco Industries Inc. and represented NETA as the principal member of NFPA Code Making Panel 13 of the National Electrical Code.