On a Saturday, at around 10 a.m., a 10t blade broke off from the rotor of a wind turbine on an 8-turbine wind farm. The operator received alarms via their safety system. A passer-by alerted the police department, which secured the area and prohibited access to the wind turbine. The entire farm was shut down. Arriving on site at around 1 p.m., the operator continued the work to make the site safe. Security was put in place from 8 p.m. for at least a week. 2 days after the fall, the operator used a drone to carry out a visual inspection of the full wind farm and surrounding fields.

Blade debris (plastic, resin, carbon, fibre glass, wood, composite materials, etc.) was found on the ground up to 40m away. Some crops (maize) in the adjoining field were damaged. A specialist company collected and treated the waste.

The blade had slid along the metal pins attaching it to the rotor. A loss of adhesion between the metal inserts linking the base of the blade to the rotor hub caused the blade to fall. This defect had been identified by the manufacturer in 2018 on a specific batch of blades identified via their serial number. Defect acceptance criteria had been determined, and the manufacturer had put in place regular ultrasound inspections to verify these criteria on the batch of blades in question. The blade’s final inspection carried out 2 months before the incident had not revealed any damage. Analysis of weather conditions in the area around the wind farm on the day of the incident showed that the loss of adhesion occurred prematurely following build-up of load phenomena: violent winds, gusts, turbulence, change of production mode to reduce noise pollution.

The classified facilities inspectorate issued an order featuring emergency measures requiring, inter alia, that the operator:

• secure access to the wind turbine;
• protect the blade to prevent debris from flying off;
• map the spread of debris;
• assess the impact of the blade’s fall on soil quality.

The operator replaced the wind turbine’s set of blades with a model of equivalent dimensions but featuring a different technology. The wind farm was authorised to start up again on condition that a restrictive operating mode be put in place to reduce load phenomena:

• turbine shutdown if winds exceed 12m/s;
• blade pitching from winds of 5-6m/s to reduce stress;
• application of a single production mode to reduce noise pollution irrespective of period and wind speed (most restrictive mode to prevent any emergence);
• monthly ultrasound inspection of blades.