Ventilation apparatus and ventilation systems primarily comprised of exhaust fans, hoods; exhaust air systems and air intake systems being ventilators for industrial purposes; gravity roof ventilators; smoke and heat extraction hood systems for industrial purposes; ventilation systems primarily comprised of exhaust fans, hoods; silencers for ventilation apparatus, exhaust air systems and air intake systems; ventilating air intake louvres and weather protection grilles for ventilation apparatu...