37 Maintenance of chemical installations, particularly of polymerization installations being air cooling apparatus, cooling installations and machines, distillation columns, drying apparatus and installations, evaporators, furnaces, heat exchangers, other than parts of machines, heating apparatus, heating installations, regulating accessories for water or gas apparatus and pipes, regulating and safety accessories for gas apparatus, regulating and safety accessories for gas pipes, regulating and safety accessories for water apparatus, safety accessories for water or gas apparatus and pipes, and ventilation installations and apparatus; construction of chemical plants and polymerization installations being air cooling apparatus, cooling installations and machines, distillation columns, drying apparatus and installations, evaporators, furnaces, heat exchangers, other than parts of machines, heating apparatus, heating installations, regulating accessories for water or gas apparatus and pipes, regulating and safety accessories for gas apparatus, regulating and safety accessories for gas pipes, regulating and safety accessories for water apparatus, safety accessories for water or gas apparatus and pipes, and ventilation installations and apparatus