There is provided a method and apparatus for selective removal of materials present on an object A in one or more layers B by surface abrasion by projection onto the surface of the object A of a moving fluid composed of a gas and solid particles conveyed in the gas. A lance housing is to be accommodated into the accommodation recess. The AC power is transformed with a transformer and an integrity-check signal is generated to vary a voltage of the photovoltaic array to perform an integrity check.