2.7 Confined Space & General Electrical Safety

OSHA 1910.146 — Permit-Required Confined Spaces

OSHA 29 CFR 1910.146, Permit-Required Confined Spaces for General Industry, defines a confined space as a space that (1) is large enough to bodily enter, (2) has limited or restricted means of entry/exit, and (3) is not designed for continuous occupancy. A permit-required confined space (permit space) is a confined space that also has one or more of: a hazardous atmosphere, a material that can engulf the entrant, an inward-converging taper, or any other recognized serious safety hazard.

For NETA technicians, the typical permit-required confined spaces are:

• Manholes — underground cable junctions and splice points; hazards include oxygen deficiency, methane/sewer gas, flooding, and energized cables.
• Electrical vaults — transformer and switchgear vaults; hazards include arc-flash, confined energized parts, and heat stress.
• Switchgear compartments and large enclosures — when bodily entry is required for testing or maintenance; arc-flash and shock are the dominant hazards.
• Cable tunnels and utility tunnels — long, narrow, with limited escape routes and the potential for energized cable faults.

Atmospheric Testing — The Required Order

Before an entrant may enter a permit space, the atmosphere must be tested in a specific order, because each test depends on the previous one being safe:

1. Oxygen — Acceptable range is 19.5% to 23.5%. Below 19.5% is oxygen-deficient (asphyxiation risk); above 23.5% is oxygen-enriched (greatly increased flammability). Test first because an oxygen-deficient atmosphere can prevent the flammable sensor from reading accurately, and an oxygen-enriched atmosphere can cause a flammable reading to be misleading.
2. Flammables — The lower explosive limit (LEL) must be below 10% (some employers use 0% as the action level). Test with a combustible gas indicator. Test second because the combustible sensor needs oxygen to operate.
3. Toxics — Test for the specific toxic gases likely to be present. In electrical vaults and manholes, the common toxics are carbon monoxide (CO) and hydrogen sulfide (H₂S) from decaying organic matter, and in battery rooms, hydrogen gas (flammable and explosive at 4% LEL). Test third because the toxic sensors also need a safe oxygen level to operate.

The testing is done with a calibrated, direct-reading gas monitor. The monitor is bump-tested against a known concentration each day before use and calibrated per the manufacturer's schedule. The atmosphere is tested before entry and continuously while the entrant is inside, because conditions can change (a gas leak, a flood, a cable fault can all alter the atmosphere).

Attendants and Rescue Plans

A permit-required confined space entry requires three roles:

• Entrant — the person who enters the space. There may be more than one, but at least one attendant is always outside.
• Attendant — stays outside the space at all times, maintains communication with the entrant(s), monitors the atmosphere, and initiates rescue. The attendant never enters the space to attempt rescue — that is a leading cause of confined-space multiple fatalities.
• Entry supervisor — authorizes the entry, verifies the permit, and cancels the permit when the work is done.

The rescue plan must be in place before entry. It may be a non-entry rescue (a retrieval line and a mechanical device to pull the entrant out) or an entry rescue by a trained rescue team. Self-rescue is always the first option — the entrant exits immediately if symptoms or monitor alarms occur. Non-entry rescue with a tripod and retrieval line is the standard for manhole work.

Exam trap: "Enter alone to save time" and "rely on ventilation from nearby fans only" are common wrong answers. The entrant never enters alone, and ventilation alone does not eliminate the need for atmospheric testing and a permit.

Approach-Distance Sources for MV Work

A NETA technician working at medium voltage must know the authoritative sources for minimum approach distances:

• OSHA 1910.269 Table R-6 through R-9 — Minimum approach distances for electric power generation, transmission, and distribution work, by voltage range and by whether the work is phase-to-ground or phase-to-phase.
• NFPA 70E Table 130.4(E) — Approach boundaries for general-industry electrical work, by voltage and by movable-conductor vs fixed-circuit-part.

Both sources define the Limited Approach Boundary (the distance an unqualified person may not cross) and the Restricted Approach Boundary (the distance a qualified person may not cross without energized-work controls). For a common 480 V live bus, the Limited Approach Boundary is 3 ft 6 in per NFPA 70E; for 15.1-36 kV, it is 10 ft for movable conductors and 6 ft for fixed circuit parts. The two standards are not always numerically identical — use the one that applies to the work you are doing.

General Housekeeping and Electrical Safety

General housekeeping is part of electrical safety and is graded on NETA exams:

• Walkways clear — test leads, tools, and debris must not create trip hazards or block escape routes.
• Cables labeled — de-energized and energized conductors must be clearly identified; misidentification is a leading cause of electrical accidents.
• Test area controlled — barriers, signs, and an attendant control access to the test area.
• Tools inspected — insulated tools must be visually inspected before each use and dielectrically tested periodically.
• Lighting adequate — work in dim light leads to contact errors and missed hazards; temporary lighting in confined spaces must be rated for the atmosphere.
• Documentation — as-found and as-left conditions are recorded per NETA work practice; a clean work area is part of a professional test report.

Housekeeping is not a soft skill — it is a recognized element of NFPA 70E and OSHA compliance, and a NETA ETT Level 2 candidate is expected to know it.