Site Hazards & Risk Assessment Flashcards

A crane operator is setting up near an energized 115 kV overhead transmission line. The minimum safe approach distance (SAD) per OSHA 1926.1408 for this voltage is 10 feet. During a lift, a gust causes the boom to encroach within 12 feet of the line. What is the CORRECT immediate action?

Answer: Stop all operations immediately, alert the crew, and do not resume until the encroachment zone is re-evaluated and cleared

Even though 12 feet exceeds the 10-foot SAD, the unplanned encroachment means the operation is no longer within a controlled safety envelope. OSHA 1926.1408 requires stopping all operations immediately when any unplanned encroachment occurs. The 10-foot SAD is a minimum under controlled, pre-planned conditions — an unplanned approach voids the prior risk assessment and requires a full re-evaluation before work resumes.

During a pre-lift site assessment, the crane inspector finds a subsurface utility map marked 'as-built – 1987.' Ground-penetrating radar (GPR) was not performed. The soil is saturated clay from recent rainfall, and the crane will operate within 15 feet of a marked gas main. What risk factor is MOST likely to be underestimated using only the 1987 map?

Answer: The current depth of the gas main due to decades of soil settlement and utility relocation

As-built drawings from 1987 may not reflect subsequent utility relocations, depth changes due to soil consolidation/heave, or additional installations. Saturated clay is particularly prone to settlement and lateral soil movement, which can shift buried utilities significantly from their mapped positions. The combination of an aged reference document and altered soil conditions makes the current depth and position of the gas main the most critically underestimated risk — GPR or vacuum excavation is required to confirm actual location.

A mobile crane is positioned on a freshly compacted gravel pad rated for 4,500 psf. The crane manufacturer's outrigger float specifications require a maximum ground bearing pressure (GBP) of 3,800 psf for the planned lift. An engineer approves the pad. Mid-lift, one outrigger float begins to slowly sink. What is the MOST likely root cause that a standard GBP calculation would have FAILED to account for?

Answer: Dynamic load amplification from sudden crane movement or load swing increasing instantaneous GBP beyond the static calculation

Static GBP calculations assume the load is perfectly still, but real lifts involve dynamic forces: boom slew, load swing, trolleying, and even wind-induced motion all create transient spikes in bearing pressure that can significantly exceed the static value — sometimes by 25–50% or more. If the pad was engineered only to the static GBP of 3,800 psf but dynamic amplification drove instantaneous pressure to 4,200 psf or higher, the rated capacity of the pad is exceeded even though the static numbers appeared safe. This is a common and dangerous gap in field site assessments.

A lift director is conducting a risk assessment for a pick-and-carry operation on a sloped paved surface. The crane manufacturer's load chart allows pick-and-carry on slopes up to 1% grade. The measured surface slope is 0.8%, which appears acceptable. What additional site hazard is MOST critical to assess before approving this operation that is frequently overlooked?

Answer: Whether the pavement has subsurface voids, delamination, or inadequate sub-base that could cause localized collapse under dynamic travel loads

Surface slope is a necessary but insufficient criterion for pick-and-carry risk assessment. Paved surfaces can appear sound while concealing subsurface voids (from utility trenches, erosion, or deteriorated sub-base) that can catastrophically collapse under the dynamic loads of a traveling crane — loads that are far higher than static parked loads. The 0.8% grade may be within spec, but if the sub-base fails, slope becomes irrelevant. ASME B30.5 and best practices require assessment of the pavement's structural integrity, not just its surface geometry.

A crane is operating inside a partially enclosed structure. During the lift plan, the wind speed at the site perimeter is measured at 18 mph and deemed acceptable per the manufacturer's limits of 20 mph. Once the crane is positioned inside the structure with openings on two opposing sides, what phenomenon can create a site hazard that the perimeter wind reading does NOT capture?

Answer: Venturi effect through the structural openings, which can accelerate local wind speeds significantly beyond the measured perimeter value

The Venturi effect occurs when wind passes through a restricted opening (such as two openings on opposite sides of a building), causing the air to accelerate as it is forced through the narrower channel. The local wind speed at the load and boom can be dramatically higher than the wind speed measured in the open perimeter — sometimes doubling it. At 18 mph perimeter wind, the actual wind on the load inside could exceed 30+ mph, far past the crane's operational limit. This is a well-documented site hazard that standard perimeter anemometer readings fail to capture.

During a multi-crane lift risk assessment, the appointed lift director establishes a communication protocol requiring all swing and boom movements to be called out on radio before execution. Partway through the lift, radio communication is temporarily lost on one crane. Per best practice and ASME B30.5 guidance, what is the CORRECT course of action?

Answer: All cranes must immediately halt and hold their position; the lift must not resume until full, redundant communication is restored across all cranes

In a multi-crane lift, each crane's movement directly affects the load path, hook angles, and load distribution on every other crane. Loss of communication with any single crane means the lift director cannot coordinate movements, making independent action by any crane extremely dangerous. ASME B30.5 and engineered multi-crane lift plans require that all operations STOP and HOLD when communication is lost — no movement by any crane is permitted until full communication is restored across all units. Independent lowering (Option D) is particularly dangerous because it would shift the load onto the remaining crane unpredictably.