Which of the following is not a requirement for shelter holes?

Safety markings are typically not a requirement for shelter holes. Shelter holes are designated areas intended to provide miners protection during certain situations, and while they may benefit from clear identification, specific safety markings are not mandated by regulations.

In contrast, being clear of refuse is essential to ensure that the areas are accessible and function as intended without obstruction. Positioning shelter holes away from direct haulage paths is critical for safety, as it minimizes the risk of accidents involving moving equipment. Specific dimensional requirements help ensure that these shelters are adequate for protecting the miners occupying them. Therefore, the absence of a specific requirement for safety markings distinguishes this choice from the others that are essential for safe and effective shelter hole use.