Prohibited Approach Boundary

By R.W. Hurst, Editor

prohibited approach boundary

The prohibited approach boundary (PAB) is critical in electrical safety, particularly when dealing with energized electrical equipment. It defines the closest distance a worker can approach an exposed energized component without risking serious injury. The National Fire Protection Association (NFPA) 70E standard outlines the guidelines for establishing and adhering to approach boundaries to ensure worker safety.

The Three Limits of Approach Boundaries

NFPA 70E defines three distinct approach boundaries for electrical work:

  1. Limited Approach Boundary: This is the outermost boundary beyond which a shock hazard exists. Unqualified personnel must not cross this boundary unless escorted by a qualified person.
  2. Restricted Approach Boundary: This boundary lies within the limited approach boundary and signifies an increased risk of shock due to potential arc-over and inadvertent movement. Only qualified workers may enter this zone, and they must be adequately insulated or guarded from live parts.
  3. Prohibited Approach Boundary: The innermost boundary, where work is equivalent to making direct contact with the live part. Only qualified personnel with specific training, an approved energized electrical work permit, and appropriate arc flash PPE can cross this boundary.


What are the Requirements for Working in the Prohibited Approach Boundary?

Working within the PAB requires strict adherence to safety protocols to prevent electrical shock and arc flash incidents. The requirements include:

  1. Qualified Person: Only qualified persons with specific training in avoiding electrical hazards can work within this boundary.

  2. Personal Protective Equipment (PPE): Workers must wear appropriate arc flash PPE and shock protection equipment. This includes insulated tools, rubber gloves, and flame-resistant clothing to protect against potential incident energy and arc flash boundary hazards.

  3. Work Permit: Before commencing any work, a detailed work permit outlining the scope of the work, the hazards involved, and the protective measures required must be issued.

  4. De-energization: The electrical system should be de-energized before work begins. If de-energization is not feasible, other protective measures, such as insulating barriers or guards, must be implemented.


How to Determine the PAB?

The PAB is determined based on the voltage of the exposed energized parts. NFPA 70E provides tables that specify the distance from an exposed piece of electrical equipment for various voltage levels. For example, for systems operating at 750V to 15kV, the PAB is typically calculated to ensure that any inadvertent movement does not result in contact with live parts.

The calculation considers the potential for electrical arcing and the need to prevent any degree burn or other injuries. Incident energy analysis is often conducted to determine the appropriate boundaries and necessary PPE for workers.


Barricades and the limited and restricted approach boundaries

Barricades can be placed to demarcate the limited approach boundary and prevent unauthorized personnel from entering the hazardous zone. However, they should not be placed closer than the limited approach protection boundary, as this would restrict the movement of qualified workers who need to access the equipment. The barricades should be clearly marked and visible to ensure everyone understands the safety restrictions.

Additional Considerations

Beyond the PAB, other safety measures are essential for electrical work. These include using insulated tools, maintaining proper clearances, and de-energizing equipment whenever possible. Regular training and refresher courses on electrical safety and NFPA 70E standards are crucial for both qualified and unqualified personnel.

Understanding and respecting the PAB is vital for ensuring the safety of workers in electrical environments. Adhering to NFPA 70E guidelines, conducting thorough risk assessments, and using appropriate PPE can minimize the risk of electrical shock and arc flash injuries. Electrical safety is a shared responsibility, and every worker plays a role in preventing accidents and promoting a safe work environment.