Investigation of the wind speed threshold above which discarded cigarettes are likely to be moved by the wind

Cigarette butts thrown from passing cars often become fire ignition sources. However, this is only possible if a butt ends up on dead and dry fuels on the roadside. The current paper presents two experiments, carried out in a wind tunnel, designed to investigate the wind speed thresholds above which a butt thrown on the road is unlikely to stay on the road surface but will roll with the wind. The work was done for three road surfaces: asphalt, cement, and compacted soil. The experiments demonstrated that a lower wind speed is necessary for cigarette butts to start rolling from a still condition than the wind speed needed for whole cigarettes. Three wind speed thresholds, 0.88 m s–1 for asphalt, 1.63 m s–1 for cement, and 2.33 m s–1 for compacted soil, represent a conservative lower limit below which movement of still butts is highly unlikely. Three logistic regression equations were developed for calculating the probability that a cigarette butt thrown on the road surface under wind will continue to roll. They show that for wind speeds of less than 4.5 m s–1, a cigarette butt thrown on a dirt road is much less likely to be carried by the wind than if it was thrown on an asphalt or cement surface. The wind speed values refer to a height of 5 cm. The present paper provides a discussion of how this value relates to commonly used meteorological wind previsions. It also includes an example of how the findings can be used for fire prevention purposes.