NFPA 70E: Key Terms Electricians Should Know, Part 3

In the requirements of NFPA 70E, you will find five types of boundaries. To work safely, you must understand what they mean and what you should do in regard to each one. That starts with understanding what a boundary is. It’s a real or imagined line between two areas where one ends and the other begins. It’s often referred to as an edge or limit.

Sometimes it’s clearly defined. For example, when you open the door from the admin building and step into the factory, you have just crossed a boundary. No guesswork there.

Sometimes it’s not clearly defined; it’s more of a blurry line that is open to interpretation and may differ from situation to situation. We often see this kind of boundary in personal relationships. For example, you’re training an apprentice. There’s a “soft boundary” that limits how much negative input you give this person. To find it, you need to be aware of this person’s facial expressions, posture, and tone of voice. One person might need more confidence-boosting while another needs more feedback on whatever mistakes he is making. Simply adhering to a five negative limit or some such could blow it with both persons. Each has different boundaries.

When safety is the concern, boundaries need to be clearly defined to the extent possible. It is better to be specific and err on the side of caution rather than to feel your way through it. For example, someone is coring in the cement floor to prepare for installing a bollard. You have to work in a panel that is about 15 feet away. To protect your lungs from the fibrosis that would result from silica inhalation, how do you define the boundary? Being 6 feet away or 10 feet away is irrelevant if you are downwind of the dust cloud. So the boundary would be established by noting where the dust is physically contained (e.g., in that building) or where the concentration, exposure, and spread are effectively controlled.

The five types of boundaries in NFPA 70E are in relation to arc flash and arc blast protection. Two of those definitions can readily expand into general safety:

1. Hearing protection boundary. NFPA 70E defines this as “worker distance at which a one percent probability of ear damage exists from a 20kPA shockwave.” General safety: If you must raise your voice to hear yourself carry on your side of a conversation, hearing protection is required. In many plants, hearing protection is required at all times you are in the plant because there are so few areas where it’s quiet enough to not have it.
2. Lung protection boundary. NFPA 70E defines this as “worker distance at which a one percent probability of lung damage exists from a 70kPA (10 PSI) shockwave.” General safety: Use the appropriate mitigation measures and PPE to prevent the breathing in of silica dust, metallic dust, and other particulates that you are likely to encounter; and to prevent the breathing in of harmful gases, harmful aerosols, pathogens that you are likely to encounter.

The other three types of boundary are:

1. Arc flash. When an arc flash hazard exists, this boundary is the approach limit from an arc source at which incident energy equals 1.2 cal/cm².
2. Limited approach. This boundary is a limit that’s a distance from an exposed energized conductor or circuit part within which an electrical shock hazard exists.
3. Restricted approach. It’s the same as the limited approach, except it’s not in reference to the existence of an electrical shock hazard. It’s in reference to an increased likelihood of electrical shock, due to electrical arcover combined with inadvertent movement.

There are other boundaries to respect as well, and these are not explicitly defined in NFPA 70E:

• The don’t be there line. What’s the single best way to prevent being killed by a load accidentally dropped from a crane? Be somewhere else while the crane is operating. This logic applies to all energy sources, noise sources, and operational activities such as line flushes.
• Yellow or red tape barriers. The yellow really means go around, but you can cross it if you have a need to do so, keep your presence brief, and stay vigilant. If you need to bend some EMT and your bender is now behind another crew’s yellow tape line, either wait or move the bender. Red tape means you need special and specific permission to cross it.
• The qualified person boundary. The definition of “qualified person” is in NFPA 70E Art. 100. In essence, this person has demonstrated the skills and knowledge to perform the task and has received the relevant safety training. A much more detailed picture of this emerges when you read Sec. 110.4(A)(1) and (2). If you aren’t qualified, there’s a boundary between you and the performance of that task.
• The concentration boundary. You might think it’s only friendly to say hi when passing another person who is working in an open enclosure or stop and ask how they are doing. Don’t cross that boundary. Let people concentrate on their work. Exception: If the other person is performing an unsafe act, the boundary is erased. Ask that person to stop. Wait until that person has stopped and then move to a safe place to discuss the safety problem (e.g., don’t have the conversation in front of the exposed, energized equipment).
• The sufficient working space boundary. If there’s not sufficient space in which to safely perform the work, that cramped area has a boundary between it and you. The minimums in the OSHA tables, and those same tables appear in the NEC. But those tables are just guides. “Sufficient space shall be provided and maintained about electrical equipment to permit ready and safe operation and maintenance of such equipment” [Sec. 110.32].