//Ignored warnings from history.
The Hillsborough Panel found the safety of fans admitted to the terrace at the Leppings Lane end of the ground was "compromised at every level". From the condition of the turnstiles to the management of the crowd, alterations to the terrace, the construction of the "pens" in which fans were held, the placement of the crush barriers and the access to the fateful central pens via a tunnel with a one in six gradient. The deficiencies were "well known" and made the crush on 15 April 1989 foreseeable.
According to documents disclosed to the inquiry, there was a serious crush on the terrace at the 1981 FA Cup semi-final between Tottenham Hotspur and Wolverhampton Wanderers in which "many people were injured and fatalities narrowly avoided". New documents show following that incident there was a breakdown in the relationship between Sheffield Wednesday and South Yorkshire Police, which considered the capacity of the terrace too high at 10,100.//
Source
http://www.theguardian.com/football/2012/sep/12/hillsborough-truth-about-causes-of-disaster
Yes I know it's an old report.