Final answer:
It is false to use a workbench as a top rail and work platform on a pump jack scaffold according to OSHA regulations, which require proper guardrails to ensure safety.
Step-by-step explanation:
When using a pump jack scaffold system, it is false that the workbench can be used as not only a top rail but also a work platform. OSHA regulations require that a pump jack scaffold has a guardrail system along all open sides and ends of the platform, which includes a top rail and midrail. These guardrails must be installed to reduce the risk of falls. The workbench component of a pump jack scaffold is designed to hold tools and materials and is not intended to support workers. Using the workbench as a top rail or work platform can be dangerous and violates safety standards.