Excavations are commonplace on construction sites. They are dug in order to build foundations and to accommodate various types of installations. Although having employees working in an excavation may seem like just another part of the job, that doesn’t mean that excavations don’t present some very real dangers.
The most frequent cause of injury/death associated with this particular work environment is the cave-in. One cubic yard of soil weighs about 3,000 pounds. If workers are buried, they’ll suffocate in less than three minutes. If they somehow manage to survive, the weight of the soil will probably have caused serious internal injuries.
However, cave-ins aren’t the only hazard in excavation work. Lack of oxygen, toxic fumes, explosive gases, and buried power lines may also present serious safety risks. The best way to avoid exposing your employees to these risks is to develop a site-specific safety plan prior to beginning any work.
There are several factors to consider when examining the site where an excavation is to be dug:
- Surface debris- Identify any objects near the site that may create a hazard and be sure they are removed before digging begins.
- Soil composition- There are four types of soil composition as defined by OSHA:
- Stable rock- This is natural solid mineral matter that can be excavated and that remains intact while exposed.
- Type A soil- This is cohesive soil that has an unconfined compressive strength of 1.5 tons per square foot or more. Unconfined compressive strength means the load at which soil will fail when it’s compressed. The unconfined compressive strength can be determined by laboratory or field-testing.
- Type B soil- This is defined as cohesive soil that has an unconfined compressive strength of between 0.5 and 1.5 tons per square foot.
- Type C soil- This soil has an unconfined compressive strength of 0.5 tons per square foot or less.
- Underground utility lines- Where are the sewer, telephone, fuel, electric, and water lines located? What agencies need to be contacted to turn off the utilities until work is completed?
- Vehicle traffic- Is the excavation near a high-traffic road? This is a significant factor because frequent vibrations caused by moving vehicles could cause a cave-in.
- Stability of adjacent structures- Are there buildings, walls, or other structures that the excavation could render unstable? If so they will have to be properly supported before any digging begins.
- Water accumulation- Could water accumulate in the excavation from nearby streams, heavy rains, or a high water table? If this is a problem, how will it be alleviated?
- Atmospheric hazards- Could workers be exposed to atmospheric hazards or low oxygen levels? How will these hazards be controlled before work begins and what rescue equipment must be available in the event of an incident?
Although identifying hazards is the responsibility of all on-site employees, OSHA requires that a “competent person,” that is, someone who has been trained in soil analysis, protection methods, and excavation requirements, examine every excavation site. This person is responsible for classifying soil, determining the best method to protect workers from cave-ins, and testing for atmospheric hazards. The competent person must inspect the site and the protective system at least once a day for instability, damage, or other hazards.
