What Does
Trench Shield Mean?
A trench shield is a structure that protects workers in the event of a trench cave-in. These shields are usually made of steel or aluminum and consist of protective side sheets held in place by adjustable cross members. They are assembled at the site.
Trench shields are also referred to as trench boxes.
Safeopedia Explains Trench Shield
Trench collapses can be fatal and all precautions should be taken to ensure the safety of employees who work in them. To that end, the Occupational Safety and Health Administration (OSHA) requires the use of trench shields to protect workers involved in trenching and excavation.
The specific regulations governing the use of these shields are outlined in OSHA's Trenching and Excavation Safety guide.
Why Trench Shields Are Required
All trenches will eventually cave in or collapse if they aren't supported, trapping anything anyone within it. A cubic yard of soil can weigh the same as a car, and its collapse is capable of causing serious or fatal injuries. A trench shield, if properly installed, will protect workers during such a collapse.
Trench shields also protect workers from falling or dislodged material. This type of event does not constitute a full cave-in but nevertheless carries the risk of injury.
Trench shields are different from trench shoring, in which the walls of a trench are braced to prevent its them from collapsing. Unlike shoring, shielding a trench will not prevent it from collapsing but will protect workers if it does.
Sizing and Assembling a Trench Shield
Trench shields are available in various sizes and configurations, ranging from 6 to 40 feet in length and 4 to 10 feet in height. The type of shield needed for a given application depends on a number of factors, such as:
- Trench size and depth
- Weight of the trench shield
- Soil quality
OSHA Guidelines for Trench Shielding
The following are a few of the conditions provided in OSHA 1926.652(g) for trench shield installation and retrieval:
- The load on the shield system should not exceed its designated capacity
- Shileds should be installed to prevent hazardous movement of the soil that makes up the trench walls
- The space between the trench walls and the shield should be kept at a minimum and backfilled
- If the trench is four feet or deeper, a ladder, ramp, or other means of facilitating exit from the trench should be provided
- There should be no more than two feet between the bottom of the trench and the bottom of the shield