What should be used to ensure safe footing on penetrable surfaces?

Using spur plates is the correct choice for ensuring safe footing on penetrable surfaces. Spur plates are designed specifically to distribute the weight of the ladder over a larger area, which helps to prevent the ladder from sinking into soft or unstable ground. This is particularly important on surfaces such as grass, soil, or any other material that may not be solid enough to support the weight of the ladder and the person using it.

The effectiveness of spur plates lies in their ability to create a more stable base, reducing the likelihood of the ladder tipping or sinking, which can lead to accidents. This design feature is crucial in environments where the ground may easily give way under pressure, ensuring that the ladder remains secure and minimizes the risk of falls.

Other choices, while they serve various purposes in ladder safety, may not provide the same level of stability on penetrable surfaces. For example, rubber pads might help in some situations by providing grip, but they do not address the issue of weight distribution on softer ground. Wooden blocks and steel bases can also provide a means of support, but they are typically not as effective as spur plates in managing the risks associated with softer surfaces.