Introduction
The first instrument invented for testing electrical systems was the Megger megohmmeter patented in 1905 for evaluating insulation, arguably the most important component in an electrical system. The problem is that a megohmmeter is only effective in evaluating insulation condition in a deenergized state. Therefore, it often cannot detect conditions that can cause insulation to deteriorate or fail prematurely. Some 70 years later, thermal scanning of electrical systems was capable of testing electrical systems and equipment in an energized, operating condition and detect hot spots and identify areas that require corrective action to prevent failures. Although it’s an advantage to evaluate systems while energized, the disadvantage is the potential exposure to the two primary electrical hazards – shock and arc flash.
Shock and arc flash are the electrical hazards addressed by the NFPA 70E electrical safety standard in the workplace and relevant OSHA regulations. Among the safety considerations when performing thermography on electrical equipment are approach boundaries applicable to these hazards and the precautions necessary for the safety of both qualified and unqualified personnel.
A thermographer must know:
· How to identify these boundaries and when they apply,
· the qualifications required if it is necessary to cross them,
· the requirements for performing thermography in the presence of these hazards, and
· the applicable PPE (Personal Protective Equipment) that may be required in the presence of both existing and potential shock and arc flash hazards.
Perform Your Risk Assessment
Along with maintaining a safe working distance, it also is imperative to perform a thorough risk assessment to evaluate all recognized hazards, minimize the risk to an acceptable level, and include all hazards, not just the electrical hazards. Refer to NFPA 70E 130.4, 130.5 and Informative Annex F, and OSHA 1910.132.
Things that elevate the risk factor:
- The site has a poor safety record,
- The maintenance program is inadequate,
- Equipment is in poor condition, or
- Equipment is exhibiting symptoms of impending failure.
These elements may also cause you to determine a task is an unacceptable risk. If you determine the risk is unacceptable, either take steps to lower that risk to an acceptable level or make an informed decision not to perform the inspection at all.
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Two Distinct Electrical Hazards
Among the safety considerations when performing thermography on electrical equipment are the shock and arc flash approach boundaries applicable to both qualified and unqualified personnel.
Shock hazard boundaries are determined by voltage and do not vary. The nominal voltage varies slightly, but it is consistent. Shock is both a persistent and potential hazard. It is present whenever a circuit is energized and present if a circuit becomes energized. It requires touching or coming close enough to be touched by it.
Arc flash hazard boundaries are determined by calculation and vary according to energy level, and several electrical and physical characteristics. Energy varies according to conditions. Arc flash is only a potential hazard. Arc flash and blast are a function of the discharge of incident energy from an electrical fault. It is only present when an event occurs that triggers the release of energy. It will always come to you!
Although much different, the two have some common characteristics. Electric shock injury is determined by distance, voltage and current magnitude, exposure time, pathway and PPE voltage rating. Arc flash (and blast) injury is determined by distance, energy magnitude, exposure time, exposure area and PPE calorie rating. Distance is a key element common to both hazards.
Shock Boundaries
The shock boundaries are contained in Tables 130.4(E)(a) and (b) in the NFPA 70E. They are also usually found on an arc flash label. They are based upon nominal phase-to-phase voltage (or three phase equivalent) of the energized equipment.
The limited approach distance applies to movable and fixed conductors. Movable conductor distance almost always applies to overhead distribution and transmission lines.
Restricted approach distance applies to fixed conductors and movable conductors under a person’s control. Wiring in industrial switchgear, panels and other types of electrical equipment are considered fixed conductors even though the conductors may be flexible because they are unable to move freely. With specific exceptions, you must be a qualified electrical worker to cross either shock protection boundary.
If an unqualified worker needs to cross the limited approach boundary, a qualified worker must advise them of the possible hazards and continuously escort them while inside the limited approach boundary. Only a qualified worker can cross the restricted approach boundary. An unqualified worker is not permitted to cross the restricted approach boundary under any circumstances.
Arc Flash Boundary
The arc flash boundary is found on the arc flash label affixed to equipment or by using tables contained in the NFPA 70E although almost all facilities these days have had an arc flash study completed. Each arc flash boundary is calculated based upon several variables specific to each circuit or piece of equipment. Magnitude of the arc flash measured in calories per square centimeter per second (cal/cm2). The standard time period in physics is one second for all measurements and is understood.
It is difficult to establish a point of no injury, but it is possible to measure injury at a specific distance and energy level. A study by Dr. Alice Stoll and Dr. Maria Chianta in the 1960’s created the Stoll Curve which established the amount of energy necessary to create the onset of a second degree burn. The arc flash boundary is a distance where arc flash intensity is 1.2 cal/cm2 – the onset of a second degree burn on unprotected skin. This injury is considered a “recoverable injury” in that it will heal with no marks or scars. Arc flash PPE is required to cross this boundary. Since arc blast intensity cannot be accurately calculated, only the heat intensity is specified.
A person does not have to be a qualified electrical worker to cross the arc flash boundary, but they must be knowledgeable about arc flash hazards and proper PPE. To cross the boundary, the worker must wear PPE rated at or higher than the calories listed on the label or specified in the table. The working distance is from the static part of the body to the source of the energy discharge. The body must not be closer than the minimum working distance because the heat intensity will increase exponentially and will likely render the arc protection PPE inadequate to protect against arc flash injury.
Is Thermography Energized Work?
No, but some companies may require an Energized Electrical Work Permit (EEWP) as a safety precaution in order to open cabinets, remove covers, etc. or work in the vicinity of energized electrical equipment. This could be very cumbersome in performing a survey in a wide variety of locations. The good news is, there are exceptions!
An EEWP is required only when you will be crossing the restricted approach boundary to perform work on energized circuits using tools, making physical changes to the circuits or equipment, or if you interact with them in such a way that might present an increased likelihood of an arc flash event. Any work that does not cause a physical change in the equipment doesn’t require an EEWP.
An EEWP is not required to cross the limited approach boundary to perform thermography if a qualified person uses appropriate safe work practices and PPE per NFPA 70E and if the restricted approach boundary is not crossed. Again, the thermographer isn’t performing work on exposed, energized electrical equipment in the sense that they’re coming in contact with it, but they could get too close to it. Therefore, they must maintain their distance!
We do have to justify performing work on or in the vicinity of exposed energized circuits and in obtaining an exemption to the EEWP. Justification is pretty easy for thermographic surveys because to perform an effective survey, it is infeasible to do so unless the equipment is in operation which, of course, is energized. OSHA accepts infeasibility as a reason to grant an exception to EEWP requirements to perform thermography.
While no electrical protection is required outside of the restricted approach boundary, it is very likely that the arc flash boundary will be crossed. In addition to any general PPE that may be required, if the survey can’t be performed beyond the arc flash boundary or it isn’t possible to be beyond it (i.e., no clear space behind it), arc flash protection must be worn. However, by definition, an arc flash hazard requires a person to interact with the equipment or a condition to be present which increases the potential for an arc flash event to occur. If the person is not interacting with the equipment and a normal operating condition exists, arc flash protection isn’t required, but still may be worn as a “best practice” or because the authority having jurisdiction such as the owner or safety supervisor, for example, requires it.
Requirements for a Qualified Worker
The NFPA 70E requires a person to meet the definition of a qualified electrical worker to cross the limited approach boundary. To meet the requirements, the person must have demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations, and received safety training to identify hazards and reduce the associated risk.
So what does this mean? “Qualified” for the purposes of electrical safety is strictly safety-related and does not require a person to also be a qualified electrical craftsman! As always, required training must be sufficient to ensure the safety of the worker.
Although very convenient if the person is qualified, it isn’t required as long as the work is performed outside of the Limited Approach Boundary. As noted before, if the person isn’t qualified and needs to cross the LAB, they must have a qualified person escort them at all times. Whenever possible, the thermographer should use equipment with enough functional capability to eliminate the need to cross the LAB or complete appropriate training to allow them to cross the LAB unescorted.
The Best Solution
The real issue is distance. The farther away the thermographer is from shock and arc flash hazards, the safer they are. They should choose an instrument that, whenever possible, will give them the results they want at the safest distance from the hazard which is beyond the limited approach boundary (if there is exposure) and arc flash boundary.
In Summary
We now know that an EEWP is not required for some tasks inside the limited approach boundary provided that a qualified person uses appropriate safe work practices, doesn’t cross the restricted approach boundary and wears appropriate PPE to cross arc flash boundary. We know that if we comply with this, one of those allowable tasks is thermography.
If a person isn’t a qualified electrical worker, they can perform thermography inside the limited approach boundary if a qualified person escorts them, they use appropriate safe work practices, don’t cross the restricted approach boundary, and wear appropriate PPE to cross arc flash boundary, if applicable.
Regardless of the shock boundaries, if the thermographer is going to work inside the arc flash boundary, they must be able to choose and properly wear the applicable PPE, and determine when the arc flash hazard exceeds the ability of PPE to protect them. In other words, be able to determine when it is an unacceptable risk. If they will not interact with the equipment, then based upon their risk assessment, it will probably not be necessary to wear any arc flash PPE.
Electrical Safety Training
The NFPA 70E requires that a person has “training sufficient for their safety and the safety of others.” To that end, to eliminate the restrictions imposed by the qualified worker requirement, a person can take a course tailored to the specific needs of a thermographer. This would make them sufficiently qualified to cross the limited approach boundary whenever necessary and eliminate the requirement of an escort. The downside: they must take a refresher course every 3 years because the NFPA 70E is updated every 3 years..
The Thermographer’s Check List
> Determine authorization for access and if permits are required.
> Perform a risk assessment including the likelihood of occurrence.
> Identify the hazard boundaries and applicable arc flash PPE, if required.
> Maintain a safe working distance to minimize the likelihood of injury while at the same time, getting the job done safely, efficiently and in a timely manner.
Parting Safety Thought:
Distance can be your friend or your enemy.
Keep it friendly.
Keep your distance.
Written by Craig Nelson, CESW, CESCP
Senior Training Specialist
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