Which type of sign is required to alert personnel that an immediate hazard exists?

The correct answer is "Danger" because this type of sign specifically indicates an immediate hazard that can cause serious injury or even death. "Danger" signs are critical in environments where conditions are present that could lead to severe injuries or fatal accidents, and they serve to prompt immediate action to mitigate those risks.

In contrast, "Warning" signs indicate potential hazards that could cause moderate injury or property damage, while "Caution" signs alert personnel to possible hazards that may not pose immediate dangers, suggesting a need for precaution. "Notice" signs are generally used for informational purposes and do not indicate any hazards at all. Therefore, when it comes to communicating the most urgent and critical warnings to ensure safety on the job site, "Danger" signs are essential.