Disastrous events at sports grounds such as Hillsborough in Sheffield, Valley Parade in Bradford and Ibrox led to the introduction of legislation to control the safety of sports grounds. The Safety of Sports Grounds Act 1975 brought about the designation of stadia with a capacity of 10,000 or more. All designated stadia require to have a valid safety certificate and in addition require to obtain a special safety certificate in order to hold other public events, such as concerts, at the stadium.