Trenching and excavation
Planning and protection will help workers stay safe
On April 29, 2022, two brothers died when the 10-foot-deep trench they were working in collapsed. The cave-in was discovered only after the homeowner arrived to check the progress of a barn construction project near Grand Rapids, MI.
Emergency responders needed several hours to recover the bodies of the two men, both of whom worked for their family’s company.
The two deaths were among the 39 caused by full/partial trench or excavation cave-ins in 2022, according to OSHA, and they marked a sobering increase from the 15 recorded in 2021.
The spike spurred the agency to launch enhanced enforcement initiatives.
“Every one of these tragedies could have been prevented had employers complied with OSHA standards,” agency administrator Doug Parker announced in a July 14 press release. “There simply is no excuse for ignoring safety requirements to prevent trench collapses and cave-ins, and leaving families, friends and co-workers to grieve when the solutions are so well-understood.”
The hazards of trenching and excavation
The hazards of trenching and excavation are well-established. One is the sheer weight of soil. A cubic yard can weigh about 3,000 pounds. That’s as much as a car.
“The weight of soil is so heavy that it will crush you,” says a hazard alert from CPWR – The Center for Construction Research and Training. “You could die in minutes from a trench collapse, even if your head and arms are above the dirt.”
Another danger? The volatile nature of a trench or excavation. For example, water accumulation – from weather or from underground – can weaken the soil and lead to a cave-in.
“A change can happen at a moment’s notice,” said Mike Kassman, director of OSHA and disaster response training at CPWR. “It’s going to happen faster than you can react.
“A lot of folks, maybe young workers, think they can get out faster than they actually can.”
Hazards can also stem from:
- Construction equipment and machinery
- Buried electrical or gas lines
- Gases and fumes
Among the trenching and excavation deaths in OSHA’s Accident Search for 2022 were an electrocution, a worker who died of severe heat stroke, another who was struck by a falling concrete pipe and one who fell into a trench.
Is it a trench or an excavation?
OSHA defines an excavation as “any man-made cut, cavity, trench or depression in an earth surface that is formed by earth removal.” A trench, meanwhile, is “a narrow excavation (in relation to its length) made below the surface of the ground.”
Typically, a trench is deeper than it is wide, but that width when measured from the bottom is no greater than 15 feet.
“Every trench is an excavation, but not every excavation is a trench,” said Kenneth Koroll, a safety and occupational health specialist in OSHA’s Office of Construction Services.
Trenching and excavation protections
OSHA’s excavation standards are covered in 1926 Subpart P, which includes 1926.650-652 and Appendixes A-F.
Casey Perkins, assistant regional administrator of enforcement programs for OSHA Region 6, and Ralph DiNapoli, director of safety for construction company Columbia in North Reading, MA, both emphasized that OSHA standards are minimum compliance. Employers should aim to go beyond the minimum requirements – especially when it comes to trenching and excavation.
OSHA requires protective systems for excavations 5 feet or deeper, unless the excavation is composed entirely of stable rock. For excavations shallower than 5 feet, a protective system is required if a “competent person” finds any indication of a potential cave-in.
The main protective systems are:
Sloping: Cutting back the trench wall at an angle that’s inclined away from the excavation.
Benching: Forming one or a series of horizontal levels or steps into the sides of an excavation, usually with vertical or near-vertical surfaces between levels.
Shoring: Installing aluminum hydraulic or other types of supports to prevent soil movement and cave-ins.
Shielding: Using trench boxes or other supports to prevent cave-ins.
CPWR cautions that workers should never enter a trench unless it has been properly inspected. Once they’re in it, they should stay inside the protected areas only.
“Some types of soil are stable and some are not,” OSHA says. “When digging a trench, it’s important to know the type of soil you’re working with so you know how to properly slope, bench or shore the trench.”
Appendix A in 1926 Subpart P outlines the types of soils: stable rock and types A, B and C. The competent person has the responsibility of classifying the soil type.
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