Power Line Hazard Identification and Safety Procedures Flashcards

A crane operator is working near an overhead power line whose voltage cannot be determined by the employer. Under OSHA 1926.1408, what minimum approach distance (MAD) must be applied?

Answer: 20 feet, because unknown voltage must be treated as exceeding 350 kV

OSHA 1926.1408(a)(2) requires that when the voltage of a power line cannot be determined, it must be treated as if it exceeds 350 kV. Table A specifies a 20-foot MAD for lines in the 350 kV to 1000 kV range. Operations need not cease entirely — the conservative MAD allows work to continue safely.

While repositioning a lattice boom crane adjacent to an overhead transmission line, a proximity alarm activates. The operator halts movement. Under OSHA 1926.1408(c), which statement is TRUE about using a proximity alarm as an encroachment-prevention measure?

Answer: A proximity alarm must be used in conjunction with at least one other listed measure, such as a dedicated spotter or warning line

OSHA 1926.1408(c)(4) explicitly lists proximity alarms as a permissible measure but only when used in conjunction with at least one other measure from the list (e.g., dedicated spotter, elevated warning line, or insulating link). A proximity alarm alone does not satisfy the standard, regardless of its rating or voltage class.

A crane's load line contacts a 13.8 kV distribution line. A ground worker is standing approximately 8 feet away from the crane's outrigger pad. What phenomenon poses the greatest lethal risk to this ground worker, even though they are not touching the crane?

Answer: Step potential created by the voltage gradient radiating outward through the soil from the grounding point

When fault current enters the earth through the crane's outrigger or ground contact, it creates concentric rings of decreasing voltage radiating outward (ground gradient). The difference in voltage between a person's two feet — step potential — can drive lethal current through the body even with no direct contact with the crane. This is why workers must immediately shuffle away with feet together, never taking normal strides.

A crane is operating in a corridor where a 138 kV transmission line runs parallel to a de-energized and grounded 69 kV distribution line scheduled for maintenance. Which hazard specifically related to the de-energized line must the crew account for?

Answer: Induced voltage on the de-energized line from electromagnetic coupling with the energized 138 kV line

Parallel power lines can experience significant induced voltage on a de-energized conductor due to electromagnetic induction from the adjacent energized line. This induced voltage can reach dangerous levels even though the line is de-energized and nominally grounded — particularly over long parallel runs. Crane operators must treat adjacent de-energized lines as potentially energized and maintain MAD unless the utility confirms the induced voltage has been controlled.

Under OSHA 1926.1408, which scenario correctly describes when the 10-foot minimum approach distance for lines up to 50 kV may be reduced?

Answer: When the utility owner or operator has de-energized the line and it has been visibly grounded at the worksite

OSHA 1926.1408(c)(1) permits work inside the minimum approach distance ONLY when the utility owner or operator has de-energized the line AND it has been visibly grounded at the worksite. No combination of spotters, load-control devices, or engineering sign-offs substitutes for this requirement. The line must be physically rendered incapable of being re-energized during operations.

A mobile crane has just made accidental contact with an overhead power line. The boom cannot be immediately retracted. The operator is uninjured and in the cab. According to established electrical safety guidance, what is the CORRECT sequence of actions for the operator?

Answer: Remain in the cab unless fire is imminent; if egress is required, jump clear of the machine and shuffle away with feet together

The cab of a crane in contact with an energized line is actually the safest place to remain, because the rubber tires and/or structural isolation limit shock risk inside. If fire forces egress, the operator must jump — not step — clear of the machine to avoid bridging the cab-to-ground voltage gradient, then shuffle away with feet together to minimize step potential exposure. Normal dismount procedures create a lethal step-potential path between the crane and the ground.