Explains how natural ventilation can improve the environment for workers in industrial buildings as well as those in offices. States that in industrial buildings, the primary reason for installing ventilation has always been to avoid excessive internal temperatures, particularly in summer, and to provide fresh air to breath and remove odours. Waste heat from plant, processes, lighting and people is often the main problem today. Claims that natural ventilation is still an option today for cost and environmental reasons. Analysing representative values for heat load is the most demanding part of the design process. Once a heat load is established, the ventilation rate required is calculated based on the maximum acceptable temperature differential between the incoming fresh air and the outgoing stale air. Then the aerodynamic areas of inlet and exhaust ventilation have to be worked out.