Excavation and Trenching: What are the dangers?

From building a house to fixing water mains, many construction projects require workers to perform excavation work. While federal agencies like the Occupational Safety and Health Administration (OSHA) have done much to improve worker safety over the last 40 years, injuries and fatalities continue to occur.

An excavation is any man-made cut or cavity in the earth’s surface that is formed by the removal of dirt. A trench is a narrow depression in the ground that is no more than 15 feet wide and is typically deeper than it is wide. Trenches are used for a variety of civil engineering projects, ranging from pipes and roads to telephone wires.

Any construction project that moves dirt from one location to another poses a series of risks, including cave-ins, hazardous atmospheres, falling materials or objects, water accumulation and damaged underground utilities. Here is an overview of the major causes -- and preventative measures -- of each of these workplace hazards:

Cave-ins

Being caught in a trench or excavation cave-in is the leading cause of fatalities in the construction industry, and most cave-ins occur in trenches that are built for residential construction. According to OSHA, in 2011 the total number of occupational fatalities due to excavation and trenching cave-ins was 19, compared to 30 fatalities in 2007. Hundreds of workers are also injured in cave-ins each year, OSHA reports.
A cave-in occurs when a crack forms in the sidewall of the excavation, causing the wall to fall into the excavation area. Cave-ins typically happen with little or no warning, leaving workers no time to respond.
OSHA requires that contractors take specific precautions to prevent the occurrence of cave-ins, including using specific sloping techniques when constructing trenches, such as building benches to support the side walls of the excavation and placing shields between the excavation walls and the work area.

Hazardous Atmosphere

Hazardous atmospheres can also be deadly, and occur during excavations when oxygen is displaced or hazardous gasses such as hydrogen, methane or carbon monoxide enter the trench, causing poisoning, asphyxiation or even death.
To minimize the likelihood of hazardous gasses entering the excavation area, contractors should have all gas lines properly marked before starting construction.

Falling Materials or Objects

Materials or objects can fall into the excavation and hit and injure workers. In order to avoid this risk, dirt and rocks removed from the excavation -- as well as tools, pipes, equipment and other objects -- must be kept a minimum of two feet from the edge of the excavation.

Water Accumulation

Water that accumulates in excavations from rainfall or flooding can weaken the walls of the excavation, leading to structural instability, cave-ins and drowning hazards.
In order to prevent these incidents from occurring, water must be directed away from the excavation site or controlled by pumps. Workers should never work at sites where water accumulation has occurred unless adequate precautions have been taken.

Damaged Underground Utilities

Underground utilities can expose workers to a variety of hazards, including electrocution, explosions or flooding. Prior to digging with mechanized equipment, excavators are legally required to contact the local utility owner to make sure that all utilities in the area are marked. Ensuring that electrical, gas and water lines are properly marked will guarantee that none of these utilities are struck by digging equipment.
In addition to these safety measures, OSHA has done much to establish standards and best practices for excavation and trenching safety. The agency issued its first Excavation and Trenching Standard in 1971, and has since amended this standard several times in order to maintain safe worksite operations.

OSHA’s standard requires that all contractors factor the execution and cost of safety measures into their construction plans from the outset. An effective plan for minimizing workplace hazards includes establishing a system for identifying, evaluating and preventing these hazards. As part of this plan, OSHA requires that once work on the site has begun, a competent person must inspect the site for potential causes of workplace injuries on a daily basis. In addition to inspections, an on-site safety supervisor should also investigate accidents, attempt to anticipate hazards and conduct on-the-job safety and health trainings.

While OSHA is primarily focused on preventing cave-ins from occurring, the agency recognizes that workers at excavation sites are exposed to many other hazards, including falls, exposure to falling loads and mobile equipment. In order to prevent these injuries from occurring, OSHA expects contractors to ensure that: adequate warning systems are in place to alert workers that they are near the edge of the excavation; workers stand away from vehicles as they load/unload materials; mobile equipment is stored on flat ground at least two feet away from the excavation site.
Signage can also play an important role in minimizing the risk of injuries and fatalities by ensuring that those entering and working near the work site are aware of potential dangers.

To alert passersby about an excavation site, simply post a sign that reads Danger: Deep Excavation in all caps. The sign is a white rectangle, and the top third of the sign is black, featuring the word “Danger” in white in the middle of a red circle. On the bottom of the sign, the words “deep” and “excavation” appear in black lettering. Or, to warn people about an open trench, be sure to display a sign that reads Deep Trench in all caps. The sign is an orange diamond outlined in black with the message appearing in black lettering.