A multi-gigabyte disk can be erased by a child's magnet. Rooms used for magnetic storage should have a magnetic field detector at the entrance. Not only does this prevent someone entering the room with a magnet but it also prevents someone leaving the room with magnetically stored data. Many items routinely used in the office contain magnets. Accidental damage can be caused by these sources of magnetic fields.
Electric fields are less dangerous.
However a strong electronic field emitter such as a radio transmitter or a radar transmitter may damage disks. Magnetic storage can also be damaged by excessive dust, humidity, heat and cold. Generally an air-conditioned room with a dust filter on the air intake will provide an adequate environment. These are all programs which may be designed to damage the operations of a system or erase data. Others are written by people with malicious intent and seriously damage the operations of system or erase data.