A technician performing maintenance inside the hub of a wind turbine (nose that serves as a mechanical room) was injured by a flying loose part. The technician was topping up a pressurised storage tank with nitrogen. The storage tank is a 10 l cylinder with two chambers. One chamber is filled with oil and is connected to the hydraulic circuit of the turbine’s blades. The other is filled nitrogen at a pressure of around 100 bar. While finishing filling up the nitrogen chamber with a special tool he had screwed onto a coupling of the accumulator, the technician unscrewed the tank’s isolation valve instead of the tool. The sudden release of pressure flung a portion of the valve into the technician’s face, breaking his nose and several teeth and rupturing his oesophagus. The technician was helped down the nacelle by a coworker and then taken to hospital. The gendarmerie seized the accumulator as evidence and sent it in for assessment.

The manufacturer had indicated that it was hazardous to unscrew the isolation valve while the storage tank was filled with pressurised gas. A design countermeasure consisted in making a small notch on the valve’s fastener to warn technicians that a whistling sound and ice from escaping gas will form four-and-a-half turns before the valve becomes completely unscrewed and risks flying off.

An analysis conducted by the operator of the wind farm found that the warning system (notch on the fastener) on the storage tank was in place, but it was neither mentioned nor explained in the maintenance procedure. No damage to the equipment was found. It appears that the accident is due solely to organisational failures: the awareness of the hazards associated with maintaining pressure equipment, pressure-equipment training, and operating procedures in place were insufficient.

Following this accident, the operator of the wind farm revised its maintenance procedures and enhanced technicians’ training in risk assessment and management. For the time being, storage tanks in the hubs of wind turbines are now being refilled in the maintenance shop. The operator is also considering switching to tanks with built-in valves.