A Better Understanding of NFPA 70E: Conducting Risk Assessments for Electrical Safety Month
Rather than a blog on manufacturer's responsibility, this blog is about risk assessment. Once again it is May and National Electrical Safety Month, sponsored by Electrical Safety Foundation International (ESFI) to raise awareness of electrical hazards both on the job and at home, and this week I'm focusing on risk assessments.
Once a hazard is identified, it is necessary to determine if there is risk of injury. This process is called a risk assessment in NFPA 70E®, Standard for Electrical Safety in the Workplace®. Shock and arc-flash risk assessment procedures are required to be part of the documented electrical safety program. There are hundreds of valid methods of performing risk assessments for the thousands of tasks that could be conducted on the millions of pieces of equipment available. NFPA 70E is not a how-to manual for detailing a risk assessment procedure. However, what is necessary as part of an assessment is addressed. A risk assessment identifies hazards, estimates the likelihood of occurrence of injury, estimates the potential severity of injury, and determines if protective measures are required. This is the basis for any applied method of risk assessment.
Sections 110.1(H), 130.4 and 130.5 require that risk assessments be conducted before an employee begins a task. The person conducting the assessments is presented with many dilemmas. That person must identify the hazards and risks presented by different equipment, understand the training of employees, be knowledgeable of tasks to be performed, determine the operating condition of the equipment and protective devices, assess potential for human error, and verify proper equipment installation. There are many more issues, and each requires a decision. Equipment is required to be labeled with the highest voltage and incident energy or PPE category determined by the risk assessments. This protects the employee with the highest level of protection without regard for the task assigned. Without any additional criteria these are the hazards that any employee opening the enclosure must be protected from. However, a risk assessment could address other tasks performed within the equipment.
First, identify the the hazards associated with the task. A shock hazard typically exists if there is 50 volts or more. This voltage itself does not mean there is a shock hazard if the equipment is under normal operating conditions and there are no exposed energized parts. If the enclosure is opened for either justified energized work or to establish an electrically safe work condition, there might be exposure to shock hazards. There might be two separate sections within the enclosure; one with a power supply and another with control circuitry. If both sections are uncovered, the employee is exposed to the highest voltage and might be within a restricted approach boundary. But what if the power supply section is surrounded by grounded metal? Does the assessment method allow for this? Perhaps only the supply input terminals are finger-safe with a plastic cover and there are exposed 240-volt portions of the power supply. A 24-volt switching power supply might present a different hazard than a transformer supply. The task might only require access to the 24-volt control section. Capacitors and inductors in the control circuit could alter where a shock hazard exists.
Next determine the risks associated with the shock hazard. Parts operating above 50 volts may be exposed when the enclosure is opened. A cover over the supply may need to be removed to verify the absence of voltage. The interior covers may not require a tool for removal. The finger-safe plastic on the terminal may have an insulating value, or it may only be a guard. A guard should be properly spaced from energized parts and rigid enough to prevent deflection. Tools required for the assigned task might defeat the finger safe protection. The required tool might extend the shock boundary. Both the risk and hazards may be very different if the equipment is not properly maintained. The documented risk assessment procedure may not accept any less risk regardless of the task.
The arc-flash hazard and risk also need to be determined. Using the PPE category method, a piece of equipment will be marked with a minimum PPE Category 1. Using the incident energy analysis method an arc-flash hazard does not exist below 1.2 cal/cm2. Is the risk of a second-degree burn acceptable? The low incident energy might be based on a working distance of 18 inches. The hands could be nearer to the arc-flash source during performance of the task. Does an incident energy equate to an arc-flash hazard and what are the risks associated with an arc-flash capable incident energy? The control section could present a different arc-flash hazard than the supply section. Using the same equipment examples as in the previous paragraph, does an enclosure or cover remove the arc-flash hazard? Does the arc-flash hazard in the grounded metal covered supply section apply if a task is only performed within the control section? Does the arc-flash hazard exist if two specific supply points must be under a bolted fault and those two points are in separate, inaccessible sections?
Determining the maximum shock and arc-flash hazard present within an enclosure is relatively easy. These worst-case conditions are required to be on the label. The next part is why the qualification and knowledge of the person conducting a task specific risk assessment matter. The worst case can be used for 100 percent of tasks associated with the equipment. Although providing the maximum level of protection is always permitted, what about tasks in Table 130.5(C)? For example, working on 24-volt control circuits is not likely to create an arc flash when no parts above 125 volts are exposed. If the assigned task only involves the second cabinet section does the maximum arc-flash hazard present in the unopened, high-power first cabinet section apply? The employer's risk tolerance could be zero. If the risk assessment procedure is predicated on poor equipment maintenance, untrained employees, inadequate procedures, and human error, a worst-case scenario may be required for all tasks. Some risk may be tolerated. An employer's risk assessment procedure might allow a situation where access to hazards within the equipment is controlled. Interior protective covers might only be removed by a special tool that is not available to employees. However, the person conducting the assessment might consider hazards behind those covers if willful negligence is considered.
When a risk assessment determines that electrical hazards exist and there is risk to the employee, the next step is to determine the necessary protective measures. To many this means specifying personal protective equipment (PPE) but that is incorrect. The hierarchy of risk controls must be applied to further mitigate the hazard or risk. If the assessment is being conducted before equipment selection or installation, elimination, substitution, and engineering controls might be possible. Awareness requires knowledge of and possible revision of employee qualifications and training for the specific task being assessed. A detailed procedure for the task and specific equipment needs to be developed under administrative controls to address remaining hazards and risks. Implementing any of these controls may necessitate another run through the assessment to determine their effectiveness. After this, it is possible to specify required PPE. Even this requires some decision by the person conducting the risk assessment. Does the employer accept the risk of using 6.3 cal/cm2 PPE for a calculated incident energy of 6.3 cal/cm2?
NFPA 70E does not detail any of this. An entire encyclopedia might not cover it all. For an employer following NFPA 70E and OSHA regulations, the task being assessed most often should be establishing an electrically safe work condition. Remember, the purpose of these assessments is to prevent injury or death of an employee. The employer develops the risk assessment procedures to use. Those procedures must identify hazards, estimate the likelihood of occurrence of injury, estimate the potential severity of injury, and determine the required protective measures. To do so, the person conducting the risk assessment must be competent.
Next time: An Employer's Responsibility.
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