In the United States alone, hundreds of construction workers die each and every year due to accidents on the job. In most cases, these incidents are foreseeable and could have been avoided altogether had proper OSHA safety rules been followed by employers and their involved workers before and throughout their projects. In the embedded video (below), you’ll notice that around forty workers lose their lives each and every year just due to incidents associated with trenching projects. In this article, we cover the basic risks associated with trenching, as well as OSHA rules and regulations for safe employer oversight of trenching projects.
Just recently OSHA has issued a second citation to a company known as Pan Oceanic. The Chicago-based engineering company failed to protect workers from multiple trenching hazards on the job site. In November 2013, Pan Oceanic was cited by OSHA for failing to protect workers from trench cave-ins while installing water and sewer lines. However, they have been cited again this year for similar violations regarding trenching hazards at a job site in the city. According to the most recent press release, this company has since been placed on OSHA’s Severe Violator Enforcement Program. The plain and simple fact is that appropriate precautions need to be taken during each and every trenching activity. It is never okay to put the lives of employees in jeopardy to save time or money by cutting corners on acceptable trenching procedures.
Excavations in Construction/Trenching
Trenching is used in a number of construction projects, though primarily to lay down piping and other underground systems. Worker fatalities involving trenching are usually the result of a trench collapsing and crushing or suffocating workers that are trapped inside. When these incidents occur, time for escape is generally minimal and the chance of excavating trapped workers before they suffocate when held within dense soil is generally slim. Soil can be extremely heavy (weighing as much as much as 3,000 pounds per cubic meter, according OSHA’s video!), especially when damp, making it difficult to move once it has settled again. So, how can we go about preventing really, really heavy soil from posing problems to trench workers?
Trenching Safety Inspection
Before work begins, between shifts, and after any conditions (weather, etc.) changes which might affect the work being done, an inspection needs to be made by a qualified individual. A “qualified” individual is not only knowledgeable about the risks associated with trenching work and loose soil, but who also has the authority to stop or pause work when a danger is spotted. Usually, this will be a safety manager or work foreman. Inspectors should be able to recognize things like…
The 4 types of soil: In trenching, different materials you might be digging in are divided up by their danger or risk of shifting and collapse. Any solid rock being dug into presents the least amount of risk, while type A, B, and C soils are progressively more dangerous. These ratings are based on the sediments likelihood to give way. Inspectors should be able to identify the different type of soil, or cases in which multiple types are in one dig site, and know which preventative measures to setup accordingly. At a minimum, both a visual AND a touch-test of the soil should be conducted by the inspector to assess its movement. Regardless of the material, some preventative measures will need to be taken, especially at increasing depths.
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Measures to prevent cave-ins need to be implemented in any trench deeper than five feet, unless it is comprised entirely of solid rock with no risk of collapse. It is worth noting, however, that even solid rock can only have wall angles of 90 degrees, so there should never be overhang (a trench base being wider than its opening at the top. Below are are a four different protective systems recommended by OHSA and how they can help protect employees from cave-ins or collapses.
Sloping: When digging trenches more than five but less than 20 feet deep, workers can protect themselves against the risk of cave-ins simply by sloping the side walls of their trench outward. For each level of soil, the required degree of the slope changes, as dictated by OSHA rules. This is to accommodate increased shifting expected of more dangerous soil types like B and C soils. Sloping should be fully completed before a worker ever enters the trench and should be re-done if shifting or additional depositing occur at any time.
Shoring Systems: Another common type of cave-in protection comes in the form of shoring systems. These are often hydraulic arms that can be extended to press against each side of a trench. Spaced at the recommended distances through a trench, these devices stop the walls from moving inward toward the workers. Sometimes these systems incorporate metal or wooden plates to help each hydraulic setup exert force on a greater surface area.
Trench Boxes: Trench boxes, also known trenching shields, work much like hydraulic systems but are generally created at a fixed size, or at least are set up at their desired size before being place into a trench, rather than being extended once in place like a hydraulic shoring system. Trench boxes generally consist of four legs in between large metal plates which, again, protect workers from dirt collapsing in on them. It’s important trench boxes adequately cover the entire height of the trench so that dirt cannot still fall in over the top of them. Sometimes this means stacking multiple systems. To prevent possible danger from individual box pieces moving, consider finding products that already interlock (or ensure that you have a method to prevent moving and slippage).
Benching: A fourth method, benching, involves cutting or digging the sides of trenches out like steps. This not only helps to prevent cave-ins, but can also make getting in and out of trenches without the use of a ladder much easier.
According to OSHA, however, trenching safety doesn’t just stop with initial inspection and cave-in prevention measures:
Additional hazards include working with heavy machinery; manual handling of materials; working in proximity to traffic; electrical hazards from overhead and underground power-lines; and underground utilities, such as natural gas. The following references aid in recognizing and controlling some of the hazards associated with trenching and excavation…
OSHA - Trenching Safety
For more of these specifics on OSHA’s rules and regulations, and to see expansions upon individual topics touched on both in the video and in this article, be sure to check out their official page for trenching safety rules. Also, make sure you check out Creative Safety Supply for all your safety needs.