a novel locking mechanism the invention will be described in detail below with reference to the accompanying drawings referring now to fig1 an isometric view of the disposable safety scalpel according to the invention is shown with the blade being displayed in a cutting or operating position the housing 1 is provided with a groove 3 which holds the blade carrier 2 the blade carrier 2 is provided with a knob 4 which is slideable in the groove 3 from a first in use position 5 to a second pass position 6 and after use to a final disposal position 7 where the blade is permanently locked the blade carrier 2 is also provided with a first locking means 8 to ensure locking of the blade carrier in the housing in the in use position 5 a second locking means 9 to ensure locking in the pass position 6 a third locking means 10 is provided on said blade carrier 2 to ensure permanent locking of the blade carrier 2 with the blade 11 in a retracted position not shown when the scalpel is ready for disposal as a result of the permanent disposal locking position the safety of handlers during disposal is ensured similarly the easy locking transfer between.