 After the 1968 Ronan Point explosion (a Larsen-Nielsen-type tower block partially collapsed in London) Hungarian engineers modified the original system, made the structure more compact and the joints stronger.The Larsen-Nielsen system was retired in Hungary in 1970.The first, experimental panel residential building was built in Dunaújváros (new industrial city) in 1961, followed by other blocks is Pécs and Debrecen in 1963.