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Contractormag 12462 Large Trench

Common Trenching and Excavation Safety Hazards

Feb. 15, 2019
No trench should cost someone their life. In this article, we will review both the risks associated with trenching and steps job sites can take to protect workers from harm.

By Amanda Lee

Every month in the US, two workers die on average from a trench cave-in. That’s 24 workers every single year—a number that doesn’t even account for the many others who are seriously injured by collapses. One of the most tragic aspects of these cases is that they were often preventable: excavation safety measures may have prevented the collapse, or at least protected the workers inside the trench.

No trench should cost someone their life. In this article, we will review both the risks associated with trenching and steps job sites can take to protect workers from harm.

The dangers of cave-ins

Cave-ins are the most significant risk to plumbers or other workers in a trench. Such an event can occur in trenches of all sizes and depths. Even relatively shallow trenches only a few feet deep are at risk for a trench collapse event.

Without protective measures to hold the soil in place, the soil and rocks on top of the walls of the trench can come down on the people inside of it, putting them in serious danger. The risk of a cave-in greatly increases when the trench is deeper than five feet or when the soil is moist from recent rain as well as when there is equipment or materials above the trench

Is five feet down really that dangerous?

A five-foot deep trench may not seem that deep. But, it’s often deep enough to kill. Soil—especially soil saturated with water—is extremely heavy. During a collapse, it comes cascading down. The sheer weight of the earth is often enough to knock a person flat, and then the pressure of a ton of dirt on top of them can crack bones.

If the buried worker survives being initially buried, they may be too disoriented (if not unconscious) or injured to dig themselves out. Then, it’s a race against time for rescue personnel and fellow workers to safely dig the individual out. In turn, the unstable trench may threaten rescuers trying to dig the worker out.

What other risks are associated with excavation work?

  • Underground utilities: Always know what’s below before you dig! Confirm that there are no electric, gas, phone or water lines below your excavation project.
  • Run tests: You’ll need to have the air inside the trench tested to confirm that it’s safe to breathe. This is especially true in deeper trenches, where toxic gases or fumes can become trapped, only to be inhaled by workers as they enter the trench.
  • Weather: If there has been any rain or moisture, your team will need to make sure the trench is safe to enter. Even a small amount of rain can saturate soil and dramatically change the nature of a pre-existing trench.

What human factors lead to trench collapses?

In a vast majority of cases, the people at the worksite are often the ones responsible for a cave-in disaster, typically by way of either ignoring, bypassing, or simply not knowing safe trenching protocol.

Workers in a hurry

Unsafe trenches are typically the result of shortcuts being taken to complete a job quickly or by a deadline. In many cases, trench cave-ins can be avoided by either sloping the sides of the trench or implementing safety measures, such as installing trench boxes. However, since both of these take time and planning, some workers and teams have instead gambled. When that happens, they’re putting their lives in the hands of factors they cannot control, such as soil stability and soil water saturation.

Lack of training

Inexperienced workers and excavators may think that if the walls of a trench look stable, they are stable. However, the appearance of such walls can be deceiving. Without the training to know this, however, workers and plumbers may not fully understand the dangers that await them inside the trench, or when they need to go about implementing safety measures. This is where an OSHA-required competent person needs to be involved to evaluate the safety of the trench.

How can those working in a trench stay safe?

There are four ways that those working in and around trenches can stay safe and get the job done right.

1.   Have an OSHA-required competent person assess the trench

This is a worker or supervisor on the project who has training in safe excavation work and has been given the authority to identify and immediately fix unsafe trench situations. This competent person should evaluate the safety of the trench in a project area on a routine basis and educate other workers on the importance of trench safety.

2.   Slope or bench the walls of the trench

This is a method often used to protect workers in shallow (between one and ten feet) trenches. By removing the trench wall, there’s a greatly reduced risk of a collapse. Think of a sloped trench as a shallow valley instead of a deep canyon.

Benching is another technique. Similar to sloping, the goal is to cut away the trench walls in such a way where they cannot collapse into the trench. With the benching technique, the team cuts “stairs” leading out of the trench. This add stability to the slope.

There are three issues with sloping and benching that often make trench shields and trench shoring devices a more attractive choice:

  • Time and expense: As mentioned earlier, adding sloping or benching to a trench can be time-consuming, which can increase project costs.
  • Precision: The type of soil influences the angle the slope needs to be cut at for this method. The aforementioned competent person will need to evaluate if the slope is angled correctly for safe entry into the trench.
  • Depth: The deeper a trench, the more dirt will need to be removed to slope or bench it. In such cases, trench shoring may be more appropriate.

3.   Trench boxes

Also known as “trench shields,” these are steel walls that line the trench on either side. They are held apart by spreaders.

Often, trench shields and trench shoring are talked about as if they’re synonymous. Here’s the difference: trench shields will ultimately not prevent every trench collapse but will help protect the workers in the trench from harm. Trench shoring, on the other hand, can prevent collapses altogether. Typically, the supports within a trench shoring system are hydraulic, and are able to support the enormous weight of collapsing earth from pouring into the trench.

The OSHA-required competent person on the job will measure soil, weather, and other factors to determine what level of protection is needed for the site.

4.   Speak up

Never enter an unprotected trench under any circumstances. Make it known to coworkers and supervisors that an unprotected trench is unsafe and that others should not enter. If there are others on your team without excavation safety training who are working in trenches, encourage them to get training and become aware of the dangers.

Become an advocate for excavation safety

By helping enforce safety standards at your worksite, you can help prevent deaths and injuries associated with trench collapse. To learn more about trench safety, visit the OSHA website.

Amanda Lee is the senior editor and communications specialist at King Heating, Cooling and Plumbing, a professional HVAC & plumbing company based in Oak Forest, IL. Besides plumbing topics, she also enjoys writing about plumber’s safety and common trenching safety hazards. Amanda has a Bachelor’s degree in construction management and has been within the industry for almost 10 years

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