Metallic interconnects in solid oxide fuel cells are exposed to a dual environment: fuel on one side (i.e. H2 gas) and oxidizer on the other side (i.e. air). It has been observed that the oxidation behavior of thin stainless steel sheet in air is changed by the presence of H2 on the other side of the sheet. The resulting dual environment scales are flaky and more friable than the single environment scales. The H2 disrupts the scale on the air side. A model is presented where hydrogen diffusing through the stainless steel sheet reacts with oxygen diffusing through the scale to form water vapor, which has sufficient vapor pressure to mechanically disrupt the scale. Experiments on preoxidized 316L stainless steel tubing exposed to air/air, H2/air, and H2/Ar environments are reported in support of the model.