Van de Graaff generator

Electromagnetic interference
Sparks from electrostatic machines of all types are prodigious sources of electromagnetic interference, which may adversely affect the operation of nearby electronic equipment. Indeed prolonged use might contravene the Electromagnetic Compatibility Regulations.
Most importantly, anyone fitted with medical electronic equipment (eg, any type of hearing aid or pacemaker) must keep well away from a working electrostatic generator because the electromagnetic interference may cause these devices to malfunction. In practice, we recommend that, while viewing such a demonstration, a pupil wearing such equipment should keep a minimum of 6 metres from a working generator. Very occasionally, a pupil with a particular medical condition (eg, fitted with a cochlear implant) may have received specific safety advice relating to the use of electrostatic generators; this advice must be heeded.
It is wise to warn any computer users in the vicinity that a generator is to be used at a certain time and that their computer data may be corrupted as a result. Nearby computers, interactive whiteboards or similar electronic equipment (eg, a data projector) should be switched off and the generator operated well away from them.
Charging a pupil with a Van de Graaff generator
Many teachers use the Van de Graaff generator to illustrate the repulsion between ‘like’ electric charges by charging a child, to make his or her hair stand on end. This activity is very safe, provided the guidance below is followed.
Safety when charging pupils
Only a Van de Graaff generator should be used for this demonstration; Wimshurst machines must not be used. Personal electronic equipment, such as mobile phones, personal organisers and wristwatches should be kept at least 2 metres away. As a precaution, anyone with a known heart condition should not be accepted as a volunteer for this activity.
Only one child at a time should be insulated from the ground and charged. When two children are insulated and charged together, the shock experienced on discharge may be sufficient to frighten the child receiving it. No children should be persuaded to take part unless they genuinely wish to do so.
~Extracted from CLEAPSS 2008[12.9.1]