A major issue in fire safety engineering is the control and regulation of smoke production from wall linings. When a material burns it produces smoke. Smoke production has two attributes, its volume and its concentration. The smoke volume is the total amount of smoke per unit time, and is proportional to the heat release rate. The smoke concentration depends on the smoke yield of the material, which is defined as grams of smoke produced per gram of material burnt. Current two-zone models, generally accepted in fire safety design, determine whether tenability conditions are met based on smoke volume. In these models a distinct interface between the smoke and the clear layer is assumed. This paper focuses on the impact of smoke yield on tenability. Two issues are discussed (a) the variation of smoke yield with ventilation conditions and (b) the influence of smoke density gradients between the smoke and clear layer on tenability conditions. Two examples are presented to illustrate the significance of these issues.