A safety system for an elevating machine has a base part and an elevating part. The safety system includes sensor assemblies for sensing an electric or magnetic field, which are mounted on different parts of the elevating machine. A data processor is connected to receive sensor signals from the sensor assemblies. A memory stores data relating to numerous patterns of sensor signals associated with the interaction between the elevating machine and an electric or magnetic field. The data processor compares the received sensor signals with the stored data and identifies the positional relationship between the elevating machine and a source of the sensed field.