Why should apparatus be kept away from trenches?

Keeping apparatus away from trenches is crucial mainly to prevent secondary collapse. Trenches can be unstable, particularly if they are not properly shored or if the conditions change due to water incursion or other environmental factors. Heavy equipment like fire apparatus can add extra weight and pressure to the edges of the trench, potentially triggering a collapse that could endanger firefighters and others working in the area. By maintaining distance from the trench, the risk of this secondary collapse is significantly reduced, ensuring the safety of personnel on the scene.

The other options, while they may relate to operational considerations, do not address the primary safety concern regarding trench stability in the same way. For instance, water runoff management, noise pollution, and visibility are relevant to fireground operations but do not specifically pertain to the immediate structural risks associated with trenches.