Pneumatic pressure vessels, or more commonly used names, air tanks, are used for storing compressed air to operate different pneumatic tools, for example, wrenches, grinders, sanders and others. The objective of design optimization of air tanks is cost reduction, by reducing the total mass of the vessel, the quantity of the welding seams with adequate strength and stiffness. This study describes the steps of this design optimization, but also deals with high cycle fatigue, to determine the lifetime of the equipment and the effect of the fire load. The optimization was made with the Generalized Reduced Gradient (GRG) method. Nozzles with the same geometry will have a different impact on the utilization, in the various diameters of shells. Therefore, the allowed number of cycles will change. The fire load was modelled as an ISO fire and corresponding temperature/pressure increase rates were investigated.