How much weight must a portable ladder be designed to support?

A portable ladder must be designed to support a load that is four times the maximum intended load. This design requirement is based on ensuring that the ladder can reliably support not only the weight of the user but also any additional tools or materials they might be carrying while using the ladder. This extra margin of safety is crucial because it accounts for factors like dynamic loads caused by movement, potential wear and tear on the ladder, and unforeseen circumstances that might occur while the ladder is in use. Hence, designing to support four times the maximum intended load significantly enhances safety and reduces the risk of ladder failure during operation.