When is excavation below the level of a foundation footing permitted?

Excavation below the level of a foundation footing is permitted when a support system is in place. This ensures that the integrity of the existing structure is maintained while excavation is taking place. A proper support system, such as shoring or bracing, is critical to prevent collapse and protect both the workers and the equipment involved in the operation. The presence of a support system allows for safe excavation by managing the lateral soil pressures and providing stability to adjacent structures.

Options that mention supervisor approval or the availability of construction equipment do not directly address the crucial safety concerns associated with excavation work. Similarly, being within city limits does not inherently influence the safety measures that must be implemented when excavating near a foundation. Therefore, having a support system is the key requirement for safely conducting such excavations.