• Employers must address several precautionary measures to keep workers safe from falls, falling loads, and mobile equipment-related perils.
• Hazardous atmospheres or the possibility of them necessitate site testing done by a competent person, as well as controls and rescue equipment for employees.

In addition to the hazards covered in other sections, employees need to be aware of other dangers.

Falls, falling loads, and mobile equipment

Besides cave-ins and related hazards, workers involved in excavation work are exposed to dangers involving falls, falling loads, and mobile equipment. To protect employees from these hazards, the Occupational Safety and Health Administration (OSHA) requires an employer to take the following precautions:

• Keep materials or equipment that might fall or roll into an excavation at least two feet from the edge of excavations, or use retaining devices, or both.
• Provide warning systems such as mobile equipment, barricades, hand or mechanical signals, or stop logs to alert operators to the edge of an excavation. If possible, keep the grade away from the excavation.
• Provide scaling to remove loose rock or soil or install protective barricades and other equivalent protection to protect employees against falling rock, soil, or materials.
• Do not let employees work on faces of sloped or benched excavations at levels above other employees unless the employees at the lower levels have adequate protection from falling, rolling, or sliding material or equipment.
• Prohibit employees from standing or working under loads being handled by lifting or digging equipment. Require workers to stand away from vehicles being loaded or unloaded to keep them from being struck by any spillage or falling materials. Operators may be permitted to remain inside cabs of vehicles if those cabs supply adequate protection from falling loads during loading and unloading operations.

Water accumulation

Among additional hazards stemming from water in an excavation are undermining the sides and making it more difficult to get out of the excavation. The OSHA standard forbids employees to work without adequate protection in excavations where water has accumulated or is accumulating. Such precautions can include special support or shield systems to prevent cave-ins, water removal to control the water level, or the use of a safety harness and lifeline.

If water removal equipment is used to control or prevent water accumulation, an employer must ensure that a competent person monitors the equipment and its operation to ensure proper use. OSHA standards also require the use of diversion ditches, dikes, or other suitable means to prevent surface water from entering an excavation and to provide adequate drainage of the adjacent area. In addition, a competent person must inspect excavations subject to runoffs from heavy rains.

Hazardous atmospheres

A competent person must test any excavation deeper than four feet or where an oxygen deficiency or a hazardous atmosphere is present or could reasonably be expected, such as a landfill or where hazardous substances are stored nearby, before an employee enters it.

If there are any hazardous conditions, the employee must be supplied with controls such as proper respiratory protection or ventilation. In addition, when controls are used to reduce the level of atmospheric contaminants to acceptable levels, conduct testing as often as necessary to ensure the atmosphere remains safe.

If hazardous atmospheric conditions exist or may reasonably be expected to develop in an excavation, provide emergency rescue equipment such as a breathing apparatus, safety harness and line, and basket stretcher and be sure this gear is readily available. All such equipment must be attended when in use.

Note: In addition to the Excavation standard’s provisions on hazardous atmospheres in excavations, OSHA’s Confined Spaces in Construction standard (29 CFR Part 1926, Subpart AA) applies to non-excavation work within a confined space located in an excavation. These standards are intended to complement each other and address two distinct hazards: hazardous atmospheres in excavations and additional hazards associated with confined spaces located within excavations.

For example, the Confined Spaces in Construction standard covers entry into a prefabricated storm drain, other pipe, or manhole even if located at the bottom of an open excavation.

Performing certain types of work in an excavation, such as painting and welding, can expose employees to breathing dangers. In addition, equipment operating near the excavation can expose workers to breathing hazards including carbon monoxide, which bonds with human hemoglobin cells 50 times tighter than oxygen.

Oxygen can also be displaced by different gases and compounds in the trench and surrounding area. The proper level of oxygen required is approximately 21 percent (variable depending on elevation and other factors). A deficient atmosphere is less than or equal to 19.5percent oxygen, and an oxygen-enriched atmosphere is greater than or equal to 23.5% (which can cause fire and explosion). Oxygen can also be absorbed by oxidization of metal and chemical processes in a trench.