What type of safeguard prevents the operator from contacting dangerous parts while the machine is in motion?

The type of safeguard that prevents the operator from contacting dangerous parts while the machine is in motion is automatic devices. These devices are designed to activate safety measures without requiring manual intervention from the operator, thereby minimizing the risk of accidental contact with moving parts.

Automatic devices can include sensors, light curtains, and interlocks, which can detect when an operator is in a hazardous area and subsequently stop the machine's operation. These systems enhance safety by providing a barrier that reacts in real-time to unsafe conditions, ensuring that operators are kept safe from harm when the machine is running.

The other options, while valid safety measures, do not directly provide the same level of protection against contact with dangerous parts during operation. Manual control relies on the operator's actions and attentiveness, visual barriers may not entirely prevent access to dangerous areas, and lock and key systems typically secure equipment but do not actively prevent contact while the machine is functioning.