Evaluation of a new method for puff arrival time as assessed through wind tunnel modelling

Deliberate or accidental gas leakages threaten people's lives. Short-duration releases of gas are influenced by actual phase of turbulent atmospheric flow and therefore the study of these situations requires multiple repetitions of the leakage under the same mean conditions. Such a set of experiments was conducted in a wind tunnel on a scaled model of an idealized urban canopy created by rectangular buildings with pitched roofs organized into closed courtyards. Concentration time series of high time resolution were measured by a fast flame ionisation detector. The arrival time of gas from short-duration discharges was investigated at a few places of detection. This paper introduces a new method of defining gas arrival time, one not only applicable in the post-processing analysis but also in the operative stage. Moreover, it shows the results of other commonly used gas arrival time definitions (visual and dosage methods and a method utilizing the maximum detected concentration). It was explored both, the change in the arrival time value in individual realisations and places as well as the change in statistical values calculated from ensembles (mean, median, quartiles). Furthermore, the dependence of the definitions of arrival time on their parameters is discussed.