There has been a significant body of work related to understanding human behavior in fire which includes experimental and human field trials. This work is used in fire engineering designs as inputs into fire and evacuation models and the built environment to provide fire safe solutions. The application and interpretation of these parameters are particularly common in performance-based design for occupant evacuation and smoke control systems in all buildings, specifically in rapid transit and tunnel (road and rail) systems. Inconsistencies between modelling inputs, such as visibility constants, visibility criteria, and the interpretation of results have been observed to cause confusion amongst modelers and stakeholders. Occupant tenability is comprised of both visibility and irritant species. One objective of this paper is a consolidated approach to engineering calculations for determining visibility through smoke. The review evaluates the application of K factors with respect to illuminated signs or reflective surfaces, the relationship to mass extinction coefficients and acceptance criteria in various global jurisdictions. A recommendation on the method of analysis and acceptance criteria is provided. A second objective is the use of visibility outputs in engineering design and methods to interpret results to design solutions. Interpretation of visibility is a three-dimensional problem which is influenced by other external factors such as ambient lighting and other objects and surfaces. General practice is an evaluation of smoke obscuration in a discrete point. Wayfinding capability requires consideration of exit sign characteristics (luminance, location, design), ambient lighting and smoke obscuration to understand the ability for occupants to see an exit. A review of past work and recommendations is provided.