Using the proper-size trench shield for the width and depth of your excavation is vital to protectecting workers form cave-ins. On this job, two shields have been stacked and locked together to match the excavation's depth. Using the proper-size trench shield for the width and depth of your excavation is vital to protecting workers from cave-ins. On this job, two shields were stacked and locked together to match the requirements for the excavation’s depth.

Sizing an Trench Shield

Correctly sizing a trench shield is a critical step toward maximizing the safety of your workers. You must address several questions:

    • What is the excavation’s depth?
      The answer to this question will determine the height of the needed trench shield. It is possible to stack multiple shields in deeper excavations. For example, two 8′ high trench shields can be stacked to provide 16′ of vertical protection.
    • Is there room to slope part of the excavation?
      In some instances, it may be possible to use a shield to provide protection in the lower part of an excavation, and slope above the shield, to provide protection in the upper part of an excavation. However, be aware that the costs associated with sloping may far exceed acquiring the appropriate trench boxes that will reach to the top of the excavation.
    • What are the soil conditions?
      Last year, we presented a detailed, 3-part series on soils and their classification in “Excavation Safety News.” At the bottom of each story you will find a link to the next “soils” story in the series. As you will learn in that series, the type of soil you are working in (A, B, or C) will determine the depth rating(s) required for needed shield(s).
    • How much room is needed inside the shield?
      The answer to this question is typically determined by the pipe or object that is being installed or worked on in the excavation. In a pipe-laying operation, many contractors and utilities want 6″ to 12″ on each side of the pipe. For repairs, 24″ to 36″ may be needed on each side of the pipe. This distance, plus the diameter of the pipe or object, will determine the length of the needed spreaders.
    • If laying pipe, how long does the trench shield need to be in relation to the length of the pipe segments?
      Many contractors and utilities want the trench shield to be 2′ to 4′ longer than the pipe segments.
    • What is the best capacity for the excavator or backhoe that is used to move the trench shields?
      A rule of thumb is that the excavator or backhoe needs to be able to lift 1½ times (150%) the weight of the shield, at the maximum radius from the machine.

Here’s a Key Point to Remember . . .

Trench shields must be installed to prevent lateral (side-to-side) or hazardous movement of the shields. In some instances, it may be necessary to back fill around a shield to fill larger voids between outside of the trench shield and the trench wall.

In our next installment — in a couple of weeks — we’ll look at how you use the manufacturer’s tabulated data, which accompanies every trench shield.

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MS-DAMAGE-PREVENTION-CLASS-2 High-quality, effective training can saves lives. Make sure your job-site workers get safety training regularly.

Effective Safety Training Helps Prevent Fatalities

The case studies below provide real-life examples of why high-quality, effective safety training is so important. Last year, the Occupational Safety and Health Administration (OSHA) issued statements regarding citations to five companies where training might have helped save a worker’s life.

5 Incidents . . . 5 Deaths . . . All Preventable

1. In a January incident, a worker died from injuries sustained when a trench collapsed at a job site in Nebraska. OSHA proposed fines of $157,000 against the plumbing company. The company was cited for failing to train workers about trenching hazards and four other safety violations.

“This tragedy might have been prevented with the use of protective shoring that the company planned to bring to the job site that afternoon,” OSHA’s Area Director in Omaha, said. “All too often, compromising on safety procedures has tragic consequences, and hazards like these cause numerous deaths and injuries every year. No job should cost a worker’s life because an employer failed to properly protect and train them.”

2. OSHA proposed $325,710 in fines and cited a waste-treatment facility for 22 safety and health violations as a result of a December fire and explosion at the Cincinnati waste treatment facility. One worker died from his burns. The violations include failure to provide new training:

  • to employees assigned to handle waste materials,
  • to workers on the proper selection and use of personal protective equipment (PPE) for protection from various materials that are part of their routine assignments, and
  • to employees assigned to work on energized circuits.

3. Penalties totaling $116,200 were proposed against a lumber company in Texas involving a December incident in which a worker was killed after being struck by a broken band saw blade. The 17 alleged safety violations include failure to provide easily understood lockout/tagout training for energy control and to certify that energy control training was completed and current.

4. OSHA cited a trucking company in North Dakota for failing to train workers on chemical hazards and precautions after a worker was fatally injured in March while cleaning the inside of a crude oil tanker that exploded.

5. OSHA also cited tool manufacturer for 17 safety violations, including lack of training, after a maintenance worker was electrocuted in March Missouri.

Learn for These Failures. Keep Your People Trained.

Learn from the failures of these companies to protect their employees, and make needed changes in your own safety training programs to ensure such tragedies don’t happen in your workplace.

We thank the Safety Daily Advisor web site for this information.

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A Brief Introduction to . . .
Trench Shields

May 30, 2014

  OSHA defines a “trench shield” as a structure that is able to withstand the forces imposed on it by a cave-in or trench collapse, and thereby protect employees inside it. Trench shields are typically built from either steel or aluminum. Regardless of the material, the principles are the same. When to Use Which? Steel [...]

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