Acceptable wind speeds in towns

Abstract

This paper reviews the effects of wind on people, with the object of establishing limits to wind speeds which are acceptable or unacceptable. Such limits are needed for assessing conditions in towns, where tall buildings can cause troublesome winds in pedestrian areas. Observed effects of wind force are tabulated, using the Beaufort scale as a basis. These observations are supported by calculations of wind force on the human body, the unbalancing effect of this force and the effort required to progress against the wind. Existing information on thermal comfort out of doors is found to be inadequate for the present purpose, and the subject is therefore approached by considering the heat balance of the human body. From this the conditions leading to comfort can be calculated in terms of the environmental variables, air temperature, sunshine, and windspeed, and personal factors, activity and clothing. Graphs show the inter-relationship of these variables for conditions appropriate to people in shopping areas, and demonstrate the large cooling effect of the high windspeeds and shade associated with high buildings. The analysis of mechanical effects indicates that a mean speed of 5 m/sec represents the onset of discomfort, speeds greater than 10 m/sec are definitely unpleasant, and speeds greater than 20 m/sec can be dangerous. The study draws attention to several inadequacies in the available information and makes some suggestions for further work.