Low-velocity tools must be designed to be operable only against what?

Low-velocity tools are specifically designed to operate safely and effectively when used against a work surface. This design minimizes the risk of accidents or injuries by ensuring the tool remains under control and directs force appropriately against a stable surface. By requiring that these tools only function against a designated area, they promote the safe handling and operation necessary to prevent unintended consequences, such as misfires or injuries to the operator or bystanders.

In contrast, the other options do not align with the purpose and safety considerations of low-velocity tools. A tool holder may hold a tool but does not provide a stable surface for operation. A safety guard is primarily related to providing protection from the operational components of tools, rather than being a firing surface. A power source is essential for tool operation but does not dictate the surfaces against which the tool can be safely used. Thus, operability exclusively against a work surface is crucial for ensuring safety and effectiveness in using low-velocity tools.