Trenching and Excavation Safety

What are the two exceptions when a system to protect workers from cave-ins is not necessary?
When the excavation is in solid rock and therefore not a risk of caving in, and when an excavation is less than five feet deep AND a competent person has determined there is no risk of a cave-in.

What are the four primary types of soil seen when trenching and excavating, and what are their characteristics?
The four primary categories of soil are: solid rock, which is the most stable of all soils, and has almost no chance of caving in; Type A soil, which is the second-most stable soil type and is made of cohesive clay-like soil; Type B soil, which is less stable as Type A and poses a significant danger of cave-in; and Type C soil, which is the most unstable type of soil which is sandy and granular and comes apart easily.

What methods are used to protect against cave-ins caused by water?
Methods for protecting against water hazards include: special support or shield systems, water removal equipment, and us of a safety harness and lifeline.

Why is extra precaution necessary when excavating an area that has already been excavated in the past?
Pre-excavated earth has looser soil than that of undisturbed soil. This includes soil around buildings and around utility lines.

What is spoil, and how can you reduce the risk associated spoil piles?
Spoil is earth that is dug out of an excavation. To reduce risks associated with spoil piles, they must be either: kept at least two feet away from the edge of the trench, or held back by some type of retaining wall or device.

When should sloping requirements be applied to an excavation site?
When excavations are less than 20 feet deep. Anything deeper than 20 feet must be designed by a registered professional engineer.

What are some hazardous atmospheres commonly seen?
Hazardous atmospheres include: poisonous atmospheres, oxygen deficient atmospheres (less than 19.5% oxygen), combustible atmospheres, and any atmosphere that may cause death, illness, or injury to a person exposed to it.

What underground utilities must be located before digging can begin?
Electric, water, telephone, sewer, and gas lines should all be attempted to located by contacting the local utility owner.

What changes on a site would require it to be re-inspected?
They include but are not limited to: weather changes (rainstorms, thaws, earthquakes, and snowstorms), when fissures, cracks, sloughing, water seepage, or other changes are noticed, and if there is a change in the spoil pile location or size.