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.
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.
1. Soil Composition
OSHA defines different soil types and gives the unconfined compressive strength for each type. Unconfined compressive strength — how much compression the soil can take before it fails — is determined by field or laboratory testing.
The four types of soil include:
Soil types
- 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.
2. Surface Debris
All potentially hazardous objects should be identified and removed before work begins.
3. Traffic
The amount of vehicle traffic on and near an excavation site should be assessed. Vibrations from vehicles on a nearby frequently traveled roadway can increase the risk of a cave-in.
4. Underground Utility Lines
All telephone, electric, sewer, fuel, and water lines should be located. Determine which utility agencies need to be contacted for a shutoff until the work is finished.
5. Water Accumulation
Determine if there’s potential for a high water table, heavy rains, or nearby bodies of water to cause water to accumulate in the excavation. Identify a solution to eliminate or alleviate the risk, such as dewatering or proper drainage.
6. Stability Of Neighboring Structures
Know if any structures neighboring the excavation site, such as buildings and walls, could become unstable during excavation. Such structures will need to be adequately supported prior to digging.
7. Atmosphere Hazards And Low Oxygen Levels
Determine if there’s a potential for exposure to hazardous atmospheres or low oxygen. If so, plan how they will be controlled and what rescue equipment must 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 who is trained in protection methods, excavation requirements, and soil analysis since they will be directly responsible for classifying soil, performing 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. For industry safety resources and trends, see Excavation Safety and Job Growth.
Contractors and employers should also understand insurance considerations related to digging and grading; more information is available at Understanding Excavation & Grading Insurance.
Frequently Asked Questions
What is the biggest hazard in excavation work?
Cave-ins are the primary hazard and the leading cause of death and injury at excavation sites due to the weight and force of collapsing soil.
Who must inspect an excavation site?
A trained, competent person must examine the excavation site daily and after any event that could increase risk, such as heavy rain or vibrations from nearby traffic.
How can employers control hazardous atmospheres in excavations?
Employers should test the atmosphere, provide ventilation or respiratory protection as needed, and have rescue equipment and procedures in place.