My knowledge base does not contain specific information on the conditions under which a trench box or shoring system is required. However, I can provide some general safety guidance regarding trenching and excavation.

It is unsafe to enter an unprotected trench deeper than 1.2 metres (4 feet), or as specified in the legislation. [1]

If a worker is in a trench that is more than 1.2 m deep, a competent worker should be stationed on the surface to alert the worker in the trench about the development of hazards and provide assistance in an emergency. [3]

Portable trench boxes or sliding trench shields may be used for the protection of personnel in place of a shoring system or sloping. [2]

An employer shall ensure that during excavating, the walls of an excavated shaft or tunnel are retained by temporary protective structures that are adequate for the type of soil, and to prevent collapse or cave-in of the walls of the excavated shaft or tunnel. [3]

Also, remember to not start digging before locating and de-energizing the buried services. [1]

In some cases, the trench or excavation walls are made of rock but are not entirely stable. Support the walls by using rock bolts, wire mesh, or a method that provides equivalent support. [1]

Sidewalks, pavements, and appurtenant structure shall not be undermined unless a support system or another method of protection is provided to protect employees from the possible collapse of such structures. [2]

A structure that is adjacent to an excavation or trench below the level of the base or footing of any foundation or retaining wall shall be protected against settlement, lateral movement, undermining, or washout. [2]

Where the stability of adjoining buildings, walls, or other structures is endangered by excavation operations, support systems such as shoring, bracing, or underpinning shall be provided to ensure the stability of such structures for the protection of employees. [2]

Also, remember to not place the sections of pipes, piles of spoil, unused tools, and timber, and other materials within 1 metre from the trench's edge. [1]

If an employee or equipment is required or permitted to cross a trench or ditch, a walkway, runway, ramp, or bridge shall be provided. [2]

When benching the side of an excavation, the vertical rise shall not be more than 5 feet and the step back shall extend at least to the angle of repose as required by table 1. [2]

When benching a side of a trench, the height of the lower bench shall not be more than the lesser of 5 feet or width of the trench measured at the bottom. [2]

An employee shall not be permitted to work on sloped or benched excavations at levels above another employee, except when an employee at the lower level is protected from the hazard of falling, rolling, or sliding material or equipment. [2]

The angle of repose shall be flattened when an excavation has water conditions, silty materials, loose boulders, or areas where erosion, deep frost action, or slide planes appear. [2]

Employees shall be protected from the hazard of cave-ins when entering or exiting the areas protected by shields. [2]

Shield systems shall not be subjected to loads exceeding those which the system was designed to withstand. [2]

Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads. [2]

An employee shall not be allowed in shields when shields are being installed, removed, or moved vertically. [2]

Trench Boxes are commonly used in open areas that are away from utilities, roadways, and foundations. Trench boxes can be used to protect workers in cases of cave-ins, but not to shore up or support trench walls. [1]

Workers should not be present in the box when it has to be moved. [1]

If a worker is required or permitted to enter a trench, an employer shall install ladders, stairways or ramps to provide a safe means of entrance to and exit from the trench and ensure that the ladder, stairway or ramp is located not more than 8 m from a worker working in the trench. [3]