Minimum Approach Distances: What’s Required?
Let’s kick off this article with a definition of what “MAD” means in the utility sector – and it does not mean that we’re upset with you. The word is actually an acronym that stands for minimum approach distance, which is the calculated safe working distance that provides worker protection when working on or in the vicinity of energized lines and equipment.
As with other articles in this series, we must begin with the hazard. Remember, if you always begin by identifying the hazard, then the application of the OSHA standard becomes somewhat simplified. The hazard here is electricity that could result in electric shock or electrocution. Considering the consequences of the hazard, de-energization should remain the best safe work practice. When de-energization is not feasible, the hazard must be effectively controlled to provide a safe work environment. MAD has been developed to give workers a calculated safe working distance that will provide personal safety and operational security during energized line maintenance or while working in the vicinity of other energized lines. OSHA refers to MAD as “the closest distance a qualified employee may approach an energized conductor or object.”
OSHA MAD Requirements
In 2014, OSHA updated the 29 CFR 1910.269 and 1926 Subpart V standards with requirements for all employers to establish MADs. In a related move, OSHA added new information transfer requirements that obligate utilities to provide information regarding system voltage and conditions such as transient multipliers so that contract employers can calculate MAD tables for their employees. Often, utilities simply offer their own MAD calculations to the contractor. The employer is still responsible, but they can employ the MADs provided by the utility if those tables meet the requirements of the standard. OSHA provides alternative MAD tables but allows MAD to be calculated using standardized equations and engineering approaches appropriate for the workplace. Calculated MADs, especially at higher voltages, often are shorter distances than the alternative tables R-6 and R-7 in 1910.269(l). OSHA permits employers to calculate MAD for their systems because every electrical system may have different and unique factors that could affect the conditions at the work site. The employer has the responsibility to determine those factors and ensure MADs are appropriate for the actual work performed.
So, why the big changes in MAD? OSHA stated in the preamble that changes were reasonably necessary and appropriate to reduce a significant risk to workers. Data showed workers were injured by the dielectric failure of air (i.e., sparkover) between them or a conductive object they were handling and conductive objects at a different potential. Some incidents occurred when a worker or conductive object got too close to an energized part and electric current arced to the object or worker.
Understanding air as an insulator and the requirements for inadvertent movement are key to understanding how MAD plays an important role in worker safety. MAD consists of two components, an electrical component and an ergonomic component. The electrical component is the minimum air insulation distance, or MAID, required to prevent a sparkover at the work site. The ergonomic component is an “adder” used to compensate for inadvertent worker movement in relation to energized parts.
Why is air used to protect workers? Air is defined as an insulator in terms of its dielectric strength and capability to withstand electrical stresses. The dielectric strength of air is influenced by factors such as temperature, barometric pressure, altitude and relative humidity. High altitudes and hot, dry climates reduce the dielectric strength of air, requiring MADs to increase. Appendix B to 1910.269 and 1926 Subpart V, “Working on Exposed Energized Parts,” is an excellent resource to better understand MAD’s components and how they work.
IEEE 516-2009, “IEEE Guide for Maintenance Methods on Energized Power Lines,” provides engineering and technical considerations to determine MADs. The standard describes the insulation values of air along with the factors that affect those values. The standard also addresses minimum tool insulation distance, minimum approach distance for tools and minimum helicopter approach distance.
OSHA MAD Working Rules
MAD working rules must ensure that no worker approaches or takes any conductive object closer to exposed energized parts than the established MAD, unless one of the following occurs:
- The worker is insulated from the energized part.
- The energized part is insulated.
- Appropriate live-line barehand work is performed.
Workers performing work on electric power systems face two types of electrical exposures: phase-to-ground exposure and phase-to-phase exposure.
Phase-to-ground exposure exists with respect to an energized part when the employee is at ground potential, or with respect to ground when an employee is at the potential of the energized part during live-line barehand work.
Phase-to-phase exposure exists whenever a worker or the longest conductive object handled by the worker can breach the electrical component of the MAD’s live parts energized at different phase potentials. A multitude of factors should be taken into account when determining phase-to-phase exposures, including but not limited to the work performed; physical configurations; conductor spacing; proximity of grounded objects; worker approach; worker size; tools and equipment used; length of the conductive object; mechanical loads; and wind and ice that could cause the conductor to move or fail.
Phase-to-phase exposures involve not only an electric shock hazard but also arc flash and arc blast hazards. These hazards could occur from phase-to-phase contact of conductive objects when a conductive object is dropped onto or within the electrical component of the MAD’s live parts energized at different phase potentials.
MAD plays an extremely important safety role by providing workers with a safe distance when working on or in the vicinity of energized lines and equipment. Employers have a responsibility to ensure workers know MADs and can successfully demonstrate work practices to maintain them.
About the Authors: Pam Tompkins, CUSP, CSP, is president and CEO of SET Solutions LLC. She is a 40-year veteran of the electric utility industry, a founding member of the Utility Safety & Ops Leadership Network and presently serves on the USOLN executive board. Tompkins worked in the utility industry for over 20 years and has provided electric power safety consulting for the last 20 years. An OSHA-authorized instructor, she has supported utilities, contractors and other organizations operating electric power systems in designing and maintaining safety improvement methods and strategies for organizational excellence.
Matt Edmonds, CUSP, CIT, CHST, is vice president of SET Solutions LLC. A published author with over 15 years of safety management experience, he also is an OSHA-authorized instructor for general industry and construction standards. Edmonds provides specialty safety management services for electric power organizations throughout the U.S. He has been instrumental in the development of training courses designed for electric power organizations, including OSHA 10- and 30-hour courses and SET Solutions’ popular OSHA Electric Power Standards Simplified series.
About OSHA Electric Power Standards – Simplified: Topics in this series are derived from SET Solutions’ popular OSHA electric power course offered through the Incident Prevention Institute (https://ip-institute.com). The course is designed to help learners identify standard requirements and to offer practical ways to apply the standards.
Worksite Safety, Osha Articles