Whether being done to accommodate an installation or build a foundation, excavations are common occurrences around a construction site. Just because excavations are so commonplace that they seem like just another task being accomplished by competent employees doesn’t mean that serious dangers aren’t present. Among excavation sites, cave-ins are the primary cause of death and injury. Soil can weigh upwards of 3,000 pounds per cubic yard, and can cause buried workers to suffer broken bones, concussions, internal injuries, or even suffocate within minutes. Of course, a cave-in isn’t the only danger associated with excavation work. Other hazards include: toxic fumes, buried power lines, a lack of oxygen, and explosive gases.
The best way an employer can avoid exposing their employees to the risks of excavation work is by developing a safety plan tailored to the specific site before starting any work. Start by considering the following seven areas as the site to be excavated is assessed.
- Soil Composition. OSHA defines the different types of soil composition and gives the unconfined compressive strength for each type. Unconfined compressive strength, which simply means how much compression the soil can take before it fails, is determined by either field or laboratory testing. The four types of soil include:
- Stable rock – natural solid mineral matter that remains intact as it’s exposed to excavation. An example would be sandstone.
- Type A soil – cohesive soils with an unconfined compressive strength of at least 1.5 tons per square foot. An example would be clay.
- Type B soil – cohesive soils with an unconfined compressive strength of 1.5 to 0.5 tons per square foot. An example would be angular gravel.
- Type C soil – cohesive soils with an unconfined compressive strength of 0.5 or fewer tons per square foot. An example would be sand.
- Surface Debris. All potentially hazardous objects should be identified and removed.
- Traffic. The amount of vehicle traffic on and near an excavation site should be assessed. The vibrations caused by vehicles moving across a nearby frequently traveled roadway could create a cave-in.
- Underground Utility Lines. All telephone, electric, sewer, fuel, and water lines should be located. Determine what utility agencies need to be contacted for a shutoff until the work is finished.
- Water Accumulation. It should be determined if there’s a potential for a high water table, rains, or nearby bodies of water to cause water to accumulate on the excavation site. A solution to eliminate or alleviate the risk should be identified.
- Stability Of Neighboring Structures. It’s important to know if any structures neighboring the excavation site, such as buildings and walls, could become unstable during the excavation. Such structures will need to be adequately supported prior to the excavation.
- Atmosphere Hazards And Low Oxygen levels. Determine if there’s a potential for exposure to either of these. If so, it should be determined how they will be controlled and what rescue equipment will need to be available to workers.
Hazard identification is a responsibility shared by all on-site employees. However, OSHA requires excavation sites be examined by a competent person. This examiner must be trained in areas like protection methods, excavation requirements, and soil analysis since they will be directly responsible for classifying soil, atmospheric testing, and determining how best to protect employees from cave-ins. The examiner must also inspect the protective system and excavation site for damage, instability, and hazards at least once per day.