Pyro Building P4 (Carillion Building 59) at Rhydymwyn Valley Site

The Pyro Building P4, also known as the Carillion Building 59, is a very large structure built with a reinforced concrete frame and infilled with red brickwork laid in English bond. It features seven bays on the long east and west elevations. The lower level of the west elevation originally had two openings in each bay, totaling 14, which are now blocked. The central section consists of five bays, each covered by a segmental concrete vault, while the end bays have flat roofs. The north and south elevations each have six bays visible from the outside. A square concrete tower is located on the north side above the second bay from the west. The building has undergone significant alterations, including the blocking of original openings and the addition of two large vehicle entrances on the south elevation.

Inside, the space is defined by reinforced concrete posts and features some circular openings in the roof. There are overhead rails for lifting equipment. The building is divided longitudinally into two areas: the western section is a toxic area comprising three bays, while the eastern section is a non-toxic area with two wider bays. At the north end of the non-toxic side, there are small single-storey divisions for two transformers and a switch room, along with remnants of switchgear and fire-fighting equipment.