COMFORT AND DISTRESS CRITERIA
CPP uses the widely-accepted pedestrian-level wind criteria developed by Lawson (1990). Lawson’s criteria are divided into separate categories of comfort and distress (safety). The comfort criteria allow planners to assess the usability, with respect to the wind environment, of different locations for various purposes, such as for long-duration activities (e.g., sitting at an outdoor café) or strolling on walkways. The distress (safety) criteria help to identify locations where wind speeds may be hazardous to pedestrians.
Comfort ratings are based on the larger of a mean wind speed (UMean) or a “gust-equivalent mean” wind speed (UGEM) that is exceeded 5% of the time—about eight hours per week on average. Distress (safety) ratings, used for safety assessment, are based on wind speeds that occur approximately twice per year or once per season.
The wind speeds for each category are as follows:
Comfort Sitting: <4 m/s
Standing: 4-6 m/s; or sitting for a short period
Walking: 6-8 m/s
Business Walking: 8-10 m/s; destination walking from A to B
Uncomfortable: >10 m/s
Distress
Pass/Fail: 15 m/s
Poses a hazard to frail persons, small children and cyclists: 15 m/s
Could unbalance or topple able-bodied individuals: 20 m/s
The perception of wind speeds within the comfort categories can vary by individual and by region, so opinions regarding the local wind environment should be considered when evaluating the Lawson ratings.
REFERENCES
Lawson, T.V. (1990), The Determination of the Wind Environment of a Building Complex before Construction, Department of Aerospace Engineering, University of Bristol, Report Number TVL 9025.