We describe novel compositions and methods for reducing fire and smoke hazards associated with rigid and flexible PVC. Cone calorimetry studies have identified several copper additives that are highly effective as combustion inhibitors for PVC. Mixed-metal oxides of copper(II) are especially attractive in this regard, some of which are strongly synergistic for smoke suppression when they are combined, in particular CuTi.sub.3O.sub.7 and Cu.sub.3(MoO.sub.4).sub.2(OH).sub.2. These novel combinations are useful for PVC applications wherein color is not of primary importance.