In order to provide a method of introducing auxiliary material into the flow path of a crude gas stream charged with wet-paint overspray before the crude gas stream passes through at least one filter element for separating the overspray from the crude gas stream, with which method an introduction of auxiliary material into the application region of a paint shop is reliably prevented even in the event of incorrect operation, a method is proposed, which comprises the following method steps: detecting whether there is an adequate crude gas flow through the at least one filter element; and blocking the introduction of auxiliary material into the flow path of the crude gas stream if it is determined that there is not an adequate crude gas flow.