We’ve written plenty about the dangers of digging into buried infrastructure but digging can be hazardous even when there is no buried infrastructure: holes in the ground have an unfortunate tendency to collapse, often onto the people who have been digging them, unless proper precautions are taken.
OHS Canada, the country’s occupational health and safety magazine, recently published a lengthy and sobering article on the topic.
It contains some salutary warnings from Mike Chappell, provincial coordinator of the construction health and safety program at the Labour Ministry in Toronto. "The popular belief is that if you are buried in a trench, your co-workers can jump in and somehow dig you out in time. That is not the reality,” he says.
"Soil is so heavy that when it collapses, it pushes all of the air out of the lungs of a worker. One cubic [metre] of soil can weigh as much as a car and the pressure on the chest can make it impossible for a worker to breathe, even if his or her head is above the level of the collapsed soil. You only have four, perhaps five minutes realistically to rescue a worker, and if you are covered by three or four feet of soil and try to dig that out, it’s not going to happen.”
Another useful lesson from the article is the statistic that most trench and excavation fatalities occur on small, short-duration jobs and involve companies with fewer than 10 employees. These companies typically provide little or no training and supervision of workers and, says Chappell, recommended shoring or sloping protection for trenches is often not in place.
“Some companies take the risk that the shallow holes, which are generally two to two-and-a-half metres deep, will not collapse in the day or two during which the job is being done.” He says that collapse is inevitable and likely to be sudden. It is just a question of when.
These warnings are reinforced by Safe Work Australia’s Excavation Work Code of Practice, which we reported on last week. “Ground collapse can occur quickly and without warning, giving a worker virtually no time to escape, especially if the collapse is extensive,” it says. “A buried worker is likely to die from suffocation before help arrives.” It specifies that no worker should be in the trench 1.5m deep unless support has been installed, and provides detailed specification on various support options.
Compliance with the code is mandatory and it applies to any excavation that is more than 1.5 metres deep.
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