Three workers were removing a ball valve tap in order to join two bull hoses.

After checking the line was isolated two workers held the hose while another attempted to flush the line by opening the ball valve.

When the valve was opened the pressure whipped the hose out of the workers' hands allowing it to flail around and strike one of the workers.

The NSW Resources Regulator said mine operators should consider including fixed drainage points to prevent workers from releasing stored pressure from loose hoses.

"Consider using gate valves in place of ball valves to better control the release of energy," it said.

"Workers are reminded of the risks involved in whipping hoses."