Crowd control is a public security practice in which large crowds are managed in order to prevent the outbreak of crowd crushes, affray, fights involving drunk and disorderly people or riots. Crowd crushes in particular can cause many hundreds of fatalities. Effective crowd management is about managing expected and unexpected crowd occurrences. Crowd control can involve privately hired security guards as well as police officers. Crowd control is often used at large, public gatherings like street fairs, music festivals, stadiums and public demonstrations. At some events, security guards and police use metal detectors and sniffer dogs to prevent weapons and drugs being brought into a venue.