Which safety devices must remain in place during operation?

The safety devices that must remain in place during operation are chain and drive shaft guards. These guards are critical components that protect workers from moving parts in machinery. Their primary function is to prevent accidental contact with dangerous areas of the equipment, reducing the risk of injury from entanglement or crushing.

Maintaining these guards in place ensures that the machinery operates safely and minimizes the likelihood of accidents. Properly installed guards contribute to a safer work environment by shielding workers from exposed gears, chains, and drive shafts that could pose hazards during operation. Adhering to safety regulations and best practices requires that these guards are not removed or bypassed while the equipment is in use.

In contrast, while brake systems, emergency shut-off valves, and pressure relief valves are also crucial for safe operation, the question specifically asks for devices that must remain in place during operation, making chain and drive shaft guards the most appropriate choice.