A shock hazard happens when a person is exposed to a source of electrical energy that can result in electrical shock or electrocution. This can occur through direct contact with live electrical parts or indirectly through tools, equipment, or conductive surfaces.
Key Arc Flash Protection Boundaries
NFPA 70E outlines several key boundaries designed to protect workers from electrical hazards, including shock and arc flash. These boundaries help determine the necessary level of personal protective equipment (PPE) and safe work practices.
- Limited Approach Boundary
- Definition: The Limited Approach Boundary is the distance from an exposed live part within which a shock hazard exists. Only qualified persons or those who are advised by qualified persons can cross this boundary.
- Purpose: To limit access to areas where there is a risk of electrical shock.
- Protection Requirements: Unqualified persons must stay outside this boundary unless they are under the direct supervision of a qualified person.
- Restricted Approach Boundary
- Definition: The Restricted Approach Boundary is the distance from an exposed live part within which there is an increased risk of electric shock due to close proximity. Only qualified persons with appropriate training and PPE can cross this boundary.
- Purpose: To ensure that only trained and equipped individuals work near live electrical parts.
- Protection Requirements: Qualified persons must use specific PPE, follow safe work practices, and have an approved work plan.
- Prohibited Approach Boundary (Note: This boundary has been removed in recent editions of NFPA 70E)
- Definition: Previously, the Prohibited Approach Boundary was the distance within which direct contact with live parts would be considered the same as making direct contact with the live part. This boundary required the highest level of protection.
- Purpose: To provide a final level of defense against electrical shock.
- Protection Requirements: Workers needed to have a detailed work plan, use the highest level of PPE, and have proper authorization.
- Arc Flash Boundary
- Definition: The Arc Flash Boundary is the distance from an arc source within which a person could receive a second-degree burn if an arc flash occurred. This boundary is determined by calculating the potential incident energy from an arc flash.
- Purpose: To protect workers from the thermal effects of an arc flash.
- Protection Requirements: Workers within this boundary must wear appropriate arc-rated PPE based on the incident energy level.
Establishing and Maintaining Boundaries
Before you can establish a boundary, you need to identify it. Here are the key steps to safe boundaries:
- Conduct a Risk Assessment Identify potential electrical hazards through an arc flash study to determine the appropriate boundaries as well as the PPE requirements.
- Use Warning Labels Clearly label equipment with the established boundaries and required PPE.
- Train Workers Make sure that all workers understand the significance of the boundaries and how to work safely within them.
- Implement Safe Work Practices Follow NFPA 70E guidelines and best practices for electrical safety. Make them a part of your workplace culture, so that safe practices become natural habits.
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