What is the requirement for working a limited number of men when there is no second opening?

When working in an underground mine that lacks a second opening for adequate evacuation, the regulatory requirement is to limit the number of workers to ensure safety in the event of an emergency. This requirement is critical because having a limited number of personnel helps in effectively managing evacuation processes and reducing hazards associated with potential emergencies.

The specified number of twenty is determined based on safety standards that reflect the need for quick evacuation while ensuring that resources like air supply and space are sufficient for the workers present. This limit is designed to minimize risk and concentrate safety measures, creating a manageable environment for both workers and rescue operations if necessary.

The numbers below twenty are generally seen as less risky but may not align with the established regulations that prioritize the safety of those working in volatile underground conditions. Therefore, establishing the maximum at twenty ensures that safety protocols are upheld, thus prioritizing miners' health and safety.