Lawson 1978 (UK)
Back to Pedestrian Wind Comfort and Safety
Lawson 1978 (UK) provides the comfort classification. ArchiWind pairs it with Lawson 2001 safety, because the 1978 comfort criteria documented here have no separate safety classification.
Pedestrian Wind Comfort
| Category | Threshold wind speed (mean) | Exceedance probability | Activity | Color |
|---|---|---|---|---|
| A | 1.8 m/s | ≤ 2% | Long-term Sitting | |
| B | 3.6 m/s | ≤ 2% | Short-term Sitting | |
| C | 5.3 m/s | ≤ 2% | Strolling | |
| D | 7.6 m/s | ≤ 2% | Walking Fast | |
| E | 7.6 m/s | > 2% | Uncomfortable |
Exceedance probability is the percentage of time the wind speed exceeds the threshold wind speed, after combining all wind directions. Read the table from the top: each location takes the first category whose condition it meets. Comfort is classified on the mean wind speed; the gust-equivalent mean (GEM) is used for safety only.
The original categories were expressed in the Beaufort scale. The m/s values here are approximate numerical representations used in later comparisons, not exact original SI thresholds. The activity labels follow the simplified groupings used in published comparisons of the 1978 criteria.
Pedestrian Wind Safety
Selecting this scheme uses the Lawson 2001 safety classes below. This pairing is an ArchiWind choice; reports should identify it as Lawson 1978 comfort / Lawson 2001 safety. Mean wind and gust-equivalent mean (GEM) are assessed separately, using the worse safety class.
| Category | Threshold wind speed (mean / GEM) | Exceedance probability | Meaning | Color |
|---|---|---|---|---|
| A | 15 m/s | ≤ 0.023% | Safe | |
| B | 20 m/s | ≤ 0.023% | Unsafe | |
| C | 20 m/s | > 0.023% | Dangerous |
Exceedance probability is the percentage of time the wind speed exceeds the threshold wind speed, after combining all wind directions. Read the table from the top: each location takes the first class whose condition it meets. Unsafe means winds exceed 15 m/s too often to be Safe, while the time above 20 m/s remains within the limit. Dangerous means winds exceed 20 m/s more often than the limit allows.
For an annual result, 0.023% is approximately two hours per year.