When is approval necessary for hoisting more than twenty persons at once?

Approval is necessary for hoisting more than twenty persons at once because this specific regulation is in place to ensure safety and compliance in underground mining operations. When transporting large groups of individuals, there are increased risks associated with potential accidents, equipment failure, or other emergency situations.

By requiring approval for transporting more than twenty people, organizations can implement additional safety measures, perform thorough inspections of the hoisting equipment, and ensure that there are adequate safety protocols in place. This helps to minimize the risk of injury and ensures that personnel are being moved in a safe manner.

In contrast, the other options lack the specificity and safety considerations necessary for such an operation, as they either imply a more general requirement or do not establish clear conditions under which approval is mandatory.