Ground Gradient Step Potential and PPE
For various reasons, ground gradient step potential hazards are not always considered or thought to be important. I recently received a call from a large investor-owned utility whose employees had differing opinions about using super dielectric overshoes or work boots when setting a pole in an energized line. Some people are of the opinion that if you cover up the lines with a nominal voltage-rated cover, there is no danger of an energized pole and therefore no chance of ground gradient step potential. The manufacturer’s usage suggestion for any cover is for incidental brush contact by a qualified worker, not a boom truck or pole. There is nothing in ASTM D1050, “Standard Specification for Rubber Insulating Line Hose,” stating that hoses can be used for any means or measures other than a qualified electrical worker’s personal protection from energized conductors.
Pole shields are another product believed by many to protect workers on the ground who make indirect contact with energized parts. But unless the company is an electric cooperative and lives by the required Rural Electric Safety Achievement Program, which is part of the annual compliance audit by the company that insures most electric cooperatives, the dielectric testing of Salcor line hoses does not happen. Everything, including pole shields, is rated safety equipment.
Some companies feel that rubber gloves and possibly sleeves are all they need to prevent contact. They ground their non-dielectric trucks and digger derricks, and some guard the truck for touch contact in case of accidental vehicle energization. These companies have the best intentions for their employees while also attempting to run a safety program that meets the minimum requirements of OSHA 29 CFR 1910.269(p), “Mechanical equipment.” Some have a dedicated observer, which is only required by the standard when a nonelectric boom is within the minimum approach distance, and if the operator may not be able to recognize a MAD violation.
Worth the Time Invested
I personally believe that most – if not all – of the above measures are worth the time and money invested to keep employees safe on the ground. The 1910.269(p) standard is very clear as to the minimum actions the employer must take to keep employees safe. In 1910.269(p)(4), “Operations near energized lines or equipment,” OSHA states the following.
“1910.269(p)(4)(i): Mechanical equipment shall be operated so that the minimum approach distances, established by the employer under paragraph (l)(3)(i) of this section, are maintained from exposed energized lines and equipment. However, the insulated portion of an aerial lift operated by a qualified employee in the lift is exempt from this requirement if the applicable minimum approach distance is maintained between the uninsulated portions of the aerial lift and exposed objects having a different electrical potential.
“1910.269(p)(4)(ii): A designated employee other than the equipment operator shall observe the approach distance to exposed lines and equipment and provide timely warnings before the minimum approach distance required by paragraph (p)(4)(i) of this section is reached, unless the employer can demonstrate that the operator can accurately determine that the minimum approach distance is being maintained.
“1910.269(p)(4)(iii): If, during operation of the mechanical equipment, that equipment could become energized, the operation also shall comply with at least one of paragraphs (p)(4)(iii)(A) through (p)(4)(iii)(C) of this section.
“1910.269(p)(4)(iii)(A): The energized lines or equipment exposed to contact shall be covered with insulating protective material that will withstand the type of contact that could be made during the operation.
“1910.269(p)(4)(iii)(B): The mechanical equipment shall be insulated for the voltage involved. The mechanical equipment shall be positioned so that its uninsulated portions cannot approach the energized lines or equipment any closer than the minimum approach distances, established by the employer under paragraph (l)(3)(i) of this section.
“1910.269(p)(4)(iii)(C): Each employee shall be protected from hazards that could arise from mechanical equipment contact with energized lines or equipment. The measures used shall ensure that employees will not be exposed to hazardous differences in electric potential. Unless the employer can demonstrate that the methods in use protect each employee from the hazards that could arise if the mechanical equipment contacts the energized line or equipment, the measures used shall include all of the following techniques:
“1910.269(p)(4)(iii)(C)(1): Using the best available ground to minimize the time the lines or electric equipment remain energized,
“1910.269(p)(4)(iii)(C)(2): Bonding mechanical equipment together to minimize potential differences,
“1910.269(p)(4)(iii)(C)(3): Providing ground mats to extend areas of equipotential, and
“1910.269(p)(4)(iii)(C)(4): Employing insulating protective equipment or barricades to guard against any remaining hazardous electrical potential differences.
“Note to paragraph (p)(4)(iii)(C): Appendix C to this section contains information on the hazards of step and touch potentials and on methods of protecting employees from hazards resulting from such potentials.”
Two Questions
Many of you reading this know how I think, and the two questions I’ve asked myself most about this regulation are:
- How do I get to the equipotential ground mat without a dedicated isolation path or insulating boots?
- How do I approach and access a mat without step potential hazards?
In my opinion, the best method is to not allow the boom to contact energized parts.
The company that employed me for over 40 years adopted a truck grounding program and a dielectric boot policy after an incident that claimed a lineman’s life in the early 1970s. A new equipment operator raised a boom and rotated it into a 115-kV transmission line, heating up the truck and creating a ground gradient step potential hazard. The lineman was standing approximately 40 feet from the truck, but he had his climbing tools on in preparation to climb a new pole that had just been set. He had two metal plates against the ground with his “leg irons” on. Other employees in the area who were closer to the truck were not affected by the step potential.
In the 2014 update to the OSHA 1910.269 standard, super dielectric boots, shoes and work boots were reclassified as secondary protection. At my former employer’s company, which has an annual average of over 1,000 employees in the field wearing super dielectric overshoes, there seems to be a pretty good track record of safety and safe secondary protection. The definition of “secondary protection” was introduced in stakeholder meetings prior to the 1910.269 update because the boots and shoes were rated with no method to retest them. I firmly believe that proper application, maintenance and replacement of boots if they’re worn out or damaged will help protect employees in most cases of abnormal electrical conditions that may cause ground gradient step potential hazards.
The Bottom Line
The bottom line is that whatever method a company chooses to use for worker protection from step potential hazards, the company must be able to defend itself if a worker is injured. I advise taking more than minimum measures to protect employees. Start with the PPE written certification requirement found in OSHA 1910.132(d), “Hazard assessment and equipment selection,” which reads as follows:
“1910.132(d)(1): The employer shall assess the workplace to determine if hazards are present, or are likely to be present, which necessitate the use of personal protective equipment (PPE). If such hazards are present, or likely to be present, the employer shall:
“1910.132(d)(1)(i): Select, and have each affected employee use, the types of PPE that will protect the affected employee from the hazards identified in the hazard assessment;
“1910.132(d)(1)(ii): Communicate selection decisions to each affected employee; and,
“1910.132(d)(1)(iii): Select PPE that properly fits each affected employee.”
Finally, please remember that the minimum OSHA regulations can always be enhanced by the employer if the employer is willing to enforce the additional measures.
About the Author: Danny Raines, CUSP, is an author, an OSHA-authorized trainer, and a transmission and distribution safety consultant who retired from Georgia Power after 40 years of service and operated Raines Utility Safety Solutions LLC for nearly 15 years.
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