Approach Boundaries
As part of the risk assessment process, approach boundaries should be determined. There are two shock protection boundaries; the Limited Approach Boundary (LAB) and the Restricted Approach Boundary (RAB), and one Arc Flash Boundary (AFB) that must be established in order to provide a safe distance for personnel from exposed, energized electrical components.
The Limited Approach Boundary (LAB) is the approach distance to exposed, energized electrical components within which a shock hazard exists. It is the approach limit for unqualified persons. Unqualified persons may only cross this boundary if they are under the direct supervision of a qualified person, and wearing the appropriate personal protective equipment for the hazards involved. Working within the LAB is only acceptable if an Energized Electrical Work Assessment has been completed and approved, or if the work is specifically exempt per NFPA 70E-2021 130.2(B)(3).
The LAB is determined by selecting the voltage range and exposed conductor/circuit condition (i.e. either movable or fixed, column 2 or 3) in NFPA 70E-2021 Table 130.4(E)(a) for alternating current. Use NFPA 70E-2021 Table 130.4(E)(b) for direct current.
The Restricted Approach Boundary (RAB) is the approach limit for qualified persons to exposed, energized electrical components where there is an increased likelihood of electric shock due to electrical arc-over combined with inadvertent movement. Only qualified persons may cross this boundary. A qualified person required to cross the RAB must be protected from unexpected contact with exposed energized conductors or circuit parts. Working within the RAB is only acceptable if an Energized Electrical Work Assessment has been completed and approved, or if the work is specifically exempt per NFPA 70E-2021 130.2(B)(3).
The RAB is determined by selecting the voltage range in NFPA 70E-2021 Table 130.4(E)(a) for alternating current (column 4). Use NFPA 70E-2021 Table 130.4(E)(b) for direct current.
The Arc Flash Boundary (AFB) is the distance from exposed, energized electrical components within which a person could receive a second degree burn if an electrical arc flash were to occur. The AFB is determined either through calculation or through the use of the following tables. Personnel must be wearing the appropriate arc-rated protective equipment before crossing this boundary. Arc-rating is reported as either the Arc Thermal Performance Value (ATPV) or the Energy of Break-open Threshold (EBT).
In order to determine if there is a likelihood of an arc flash occurrence, and whether protective equipment is required/recommended for a given task, identify the task in NFPA 70E-2021 Table 130.5(C). If there is a likelihood of an arc flash event occurring, NFPA 70E-2021 Table 130.7(C)(15)(a) for alternating current or table (b) for direct current can be used to determine the arc flash personal protective equipment category and the arc flash boundary based on the equipment involved. The category of personal protective equipment required is defined and detailed in NFPA 70E-2021 Table 130.7(C)(15)(c).
Note: Tables and charts referenced here are provided to personnel during Electrical Qualified Person training, or by contacting Environmental Health & Safety for more information.
If work falls outside of the parameters noted in the tables and charts referenced in NFPA 70E and the incident energy must be calculated, it must be performed by an electrical engineer and Environmental Health & Safety should be consulted for review.