A redundant and fail-safe blade system of a wind turbine includes at least one blade pitch drive and at least two power control modules for controlling the blade pitch drive. To stop the supply of bleed air irrespective of the type of the bleed air source, the safety device comprises a filter device for generating the alarm signal depending on the ground connection signal and on an opening signal from an opening signal device that indicates any opening of the bleed air supply line that is connected to the high-pressure ground connection. The joint port and the dust collection port of the muffler assembly connect to the outlet port and joint port of the air sander, respectively. The material sample remains trapped in the sample capture pocket upon sample capture element retraction.