A construction trench is a narrow excavation made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is usually not greater than 15 feet. Most often, trenching fatalities occur due to cave-ins, falling objects, the presence of toxic gases or a lack of oxygen. In addition, electrocutions or explosions can occur when workers contact underground utilities.
OSHA's trenching regulations, 29 CFR 1926.650, 651 and 652, addresses a variety of hazards such as evaluating soil conditions, selecting protective systems, contacting and communicating with utility companies to locate underground lines, planning for traffic control, and determining proximity to structures that could affect choice of protective systems.
"Key issues that should be addressed when involved in an excavation project include people working in vertical trenches often on short duration projects commonly without trench boxes or adequate shoring; not understanding how dramatically water, vibration and previously disturbed dirt impacts stability; and, the chance of rescuers getting hurt by a secondary cave-in," says Mike Hayslip, Esq., PE, CSP. Hayslip has a professional civil engineering license and is also a member of the Construction Practice Specialty of the American Society of Safety Professionals (ASSE). "The information is readily available for employers and employees alike to help ensure a safe excavation project."
In addition to the OSHA standard, voluntary national consensus standards published by the American National Standards Institute (ANSI) address excavation and the hazards associated with trenching. These include the A10.12-1995 Standard Safety Requirements for Excavation, and the A10-16-1995 (R-2001) Construction and Demolition Operations - Safety Requirements for Tunnels, Shafts and Caissons.
According to Hayslip, OSHA and ANSI standards point out how important it is that:
- Trenches be inspected by a competent person that understands the OSHA excavation standard before every shift and as new hazardous situations arise;
- All equipment associated with the excavation be checked to see that it is in good condition;
- Safe access in and out of the trench is in place;
- A rescue plan is in place, and rescue equipment is at the job site;
- The soil is evaluated to determine the correct worker-protection systems (such as shoring) that must be in place; and
- The spoil piles are kept 2 or more feet from the trench.
For more information about trenching operations on construction sites check OSHA's Web site at www.osha.gov/SLTC/etools/construction/trenching/mainpage.html, the National Institute for Occupational Safety and Health (NIOSH) at www.cdc.gov/niosh or ASSE's Web site at www.asse.org.