The presented paper contributes to solution of safety assurance in complex mechatronic systems used in theatre stage technology. The aim is to solve the problem associated with reasonably foreseeable incorrect behaviour of persons and operators of these systems by application of safety measures respecting the nature of the specific conditions in which such mechanisms are being used. Special attention is paid to development, verification and validation of software for safety elements of the programmable electronic systems used to control the stage mechanisms. The validation is shown on the implementation of the methodology during development of the functional safety system of the stage technology in the National Theatre Brno.