In what material will a fire hydrant thrust block be the largest?

The size of a fire hydrant thrust block is determined by the need to effectively counteract the thrust force created by water flow in the pipelines. Thrust blocks are generally made from materials that can bear compression and provide stability against the pressures of water movement.

In the case of peat, a fibrous material often found in wetlands, it has a much lower load-bearing capacity than more traditional construction materials like concrete or steel. Therefore, when thrust blocks are installed in areas where the ground consists predominantly of peat, they must be larger in order to compensate for the ground's reduced ability to support the weight and pressure from the hydrant and the associated water flow. The larger size is necessary to ensure that the hydrant remains stable and does not shift due to the pressures exerted on it.

Concrete, steel, or plastic would typically require smaller thrust blocks since these materials have greater strength and can better support the loads. Thus, in environments where peat is prevalent, the need for a larger thrust block arises, making this the correct choice.