These interventions are detailed in the ISPESL Circular of 16th July 1997, no.71, and can be summarised as follows:
- The substitution of parts of the lifting machine (for example: hoist, carriage, motors etc.) for others with characteristics that do not create increased strain on the structure of the machine
- every structural intervention on a machine with the aim of maintenance or restoration of its initial condition (for example repairs following damage or similar), or that reduces strain on its structure (for example reduction of the gauge of a bridge crane after moving it to other runways, etc.)
- The installation of an electromagnetic wave command system
- insertion or addition of any other safety component, based on the conditions of introduction onto the market, to an already-approved crane, for better functioning with consequent improvement of safety condition during use, keeping the equipment within the limits of use instructed by the manufacturer