New NIOSH Fact Sheet Highlights Trenching Safety

From 2000−2009, 350 workers died in trenching or excavation cave-ins—an av¬erage of 35 fatalities per year.

NIOSH recently released a fact sheet detailing how to prevent worker deaths from trench cave-ins. Workers are at risk of death from cave-ins during trenching and excavation activities. NIOSH recommends engineering controls, protective equipment, and safe work practices to minimize hazards for workers.

Description of Exposure

Workers who dig or excavate trenches are at risk of death if they enter an unprotected trench and the walls collapse. However, hazards associated with trench work and excavation are well defined and preventable. The OSHA standard for excavation and trenching, known as 29 CFR 1926 Subpart P, describes the precautions needed for safe excavation work.

There is no reliable warning when a trench fails. The walls can collapse suddenly, and workers will not have time to move out of the way. Even though small amounts of dirt may not seem treacherous, a single cubic yard of dirt can weigh more than 3,000 pounds, which can fatally crush or suffocate workers. Even small, solid pieces of dirt can cause serious injuries.

From 2000−2009, 350 workers died in trenching or excavation cave-ins—an average of 35 fatalities per year. Most incidents involve excavation work or “water, sewer, pipeline, and communications and power-line construction.” An analysis of OSHA data from 1997−2001 showed that 64 percent of fatalities in trenches occurred at depths of less than 10 feet.

Lack of a protective system was the leading cause of trench-related fatalities in a review of OSHA inspections. OSHA requires that all excavations 5 feet deep or greater make use of one of the following protective system options: (1) sloping the ground; (2) benching the ground; (3) shoring the trench with supports such as planking or hydraulic jacks; or (4) shielding the trench (using a trench box). Workers should never enter a trench that does not have a protective system in place designed and installed by a competent person.

Factors such as type of soil, water content of soil, environmental conditions, proximity to previously backfilled excavations, weight of heavy equipment or tools, and vibrations from machines and motor vehicles can greatly affect soil stability and the hazards that workers face. When the sides of trenches are shored, the type of soil and width and depth of the trench affect how far apart the supports should be spaced. Different OSHA regulations apply to the different types of supports used for shoring.

Recommendations for Employers

Pre-job Planning before the job begins:

  • Train and designate a competent person to ensure safety measures are in place.
  • Call 811 before digging so that utility lines can be marked, then “pot-hole” utilities to determine the exact location and depth before digging.
  • Have a competent person evaluate the soil to determine its stability. Because soil conditions can vary dramatically over just a few days, Appendix A of Subpart P provides techniques (roll test and thumb penetration) for evaluating the condition of the soil.
  • Plan the job layout to identify safe locations (away from the trench) for spoil piles and heavy equipment routes.
  • Have a competent person determine what type of protective system will be used for the job and schedule the steps needed to have the system complete and in place before workers enter.
  • Note that trenches greater than 20 feet deep can be more complex, and an engineer should be consulted to deter¬mine the appropriate protective system (shoring, shielding, or sloping) that should be used.
  • Ensure that workers involved in the job are trained about hazards and work practices in a language that they understand and at the appropriate literacy level.
  • Develop a trench emergency action plan [NIOSH 2006] to describe steps to be taken and to provide contact information in case of an emergency.

Safe operations during the job:

  • The competent person must inspect the excavation, adjacent areas, and protective systems each day before the start of work, as needed throughout the shift, and after ev¬ery rainstorm.
  • Notify other subcontractors who come on site of the trench location and precautions and ensure that vehicles are kept a safe distance from the excavation.
  • Ensure that ladders and other means of exit from the trench are repositioned so that ladders are never more than 25 feet away from any worker in the trench.
  • The competent person must remove workers from the ex¬cavation upon any evidence of a situation that could cause a cave-in, such as accumulation of water in the trench or protective system problems. (The competent person must also take actions for other types of hazards such as falling loads or hazardous atmospheres.)
  • Monitor other types of trench–related hazards that can occur such as falls from the edge, rigging hazards, or toxic and combustible gases.
  • Implement and enforce procedures to ensure that work in an unprotected trench is not allowed.

Workers:

  • Do not enter an unprotected trench, even for a short task.
  • Inspect the protected trench before entering.
  • Exit the trench and call the competent person if you see any evidence of problems with a protective system.
  • Do not assume there will be a warning sign before a cave in or that you will have time to move out of the way.

To view the entire fact sheet, go to http://www.cdc.gov/niosh/docs/2011-180/pdfs/2011-180.pdf.

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