To achieve drilling safety, a risk-based design of the dolly assembly control system is proposed. The risk and cost-benefit assessments are conducted to obtain information needed to make decisions about the safe design of the system. A failure modes and effects analysis (FMEA) is performed to identify and analyze the plausible hazardous scenarios by determining the failure modes of the subcomponents and their effects on the system operation. The priorities of risks are ranked by assigning a risk priority number for further investigation. Appropriate recommendations are made as risk reduction measures to achieve a more intrinsically safe design. A subsequent fault-tree analysis (FTA) is performed to provide a more quantitative risk evaluation. Monte Carlo simulations (MCSs) are conducted to determine the change of the availability between the original design and a system with recommendations adopted. For the sake of decision making, a cost-benefit assessment is performed, which demonstrated that the suggestions provided in this study are highly justifiable and strongly recommendable.