After changes to the ground's layout in 1981, its safety certificate became invalid but was not renewed, so at the time of the disaster, the ground had no safety certificate.
Its safety certificate became invalid. This was after changes to the ground's layout in 1981. Its safety certificate was not renewed. This was after changes to the ground's layout in 1981. The ground had no safety certificate. This was at the time of the disaster. This was after changes to the ground's layout in 1981.