What is a crucial safety measure when using abrasive wheels?

Turning off the power supply when not in use is indeed a crucial safety measure when working with abrasive wheels. This practice helps prevent accidental activation of the equipment, which can lead to serious injuries. Abrasive wheels can generate significant hazards when left powered on, as anyone near the machine can be exposed to the risk of coming into contact with the spinning wheel. Additionally, ensuring that the power is off allows for safer maintenance and adjustments, creating a more secure working environment.

The other practices listed, while they may be relevant to the overall safety of using abrasive wheels, do not directly address the immediate risk of unintentional machine operation. For instance, standing in the plane of rotation can expose a user to flying debris and potential impacts. Using water for cooling, while it can help reduce dust and heat, is not universally applicable depending on the material being cut or ground. Adjusting speed settings frequently could also lead to mistakes or operational instability if not done with caution. Thus, prioritizing the secure shutdown of the power supply significantly reduces the likelihood of accidental harm.