On the individual exposure from airborne hazardous releases: The effect of atmospheric turbulence
University of Western Macedonia, Department of Engineering and Management of Energy Resources, Sialvera & Bakola Str., 50100 Kozani, Greece.Journal of Hazardous Materials (Impact Factor: 4.53). 02/2008; 150(1):76-82. DOI: 10.1016/j.jhazmat.2007.04.078
One of the key problems in coping with deliberate or accidental atmospheric releases is the ability to reliably predict the individual exposure during the event. Furthermore, for the implementation of countermeasures, it is essential to predict the maximum expected dosage and the exposure time within which the dosage exceeds certain health limits. Current state of the art methods, which are based on the concentration cumulative distribution function (cdf) and require the knowledge of the concentration variance and the intermittency factor, have certain limitations especially when the exposure time becomes comparable with the peak spectral time. The proposed method aims at estimating maximum dosage as a function of the exposure time, mean concentration and the turbulence integral time scale. It is much simpler than the cdf models and it poses no restrictions on the exposure time length. One of the important consequences is that it can broaden the capability of the ensemble average computational models to estimate maximum dosage for any exposure time. The method has been tested successfully utilizing the ammonia field experiments FLADIS T16 and T17.
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- "Recently, Bartzis et al. (2008) have introduced an approach relating maximum dosage D max (Δτ) during a time interval Δτ, to parameters such as the concentration variance and the turbulence integral time scale: "
ABSTRACT: In a previous study, new approaches have been introduced in the CFD-RANS modelling, according to which the concentration time scales are estimated as a function not only of the flow turbulence time scales but also of the pollutant travel times. The new approaches have been implemented for the calculation of the concentration fluctuation dissipation time scale and the maximum individual exposure at short time intervals using the k-ζ model for turbulence parameterisation. The purpose of this study is to implement and validate again the new methodology using the widely known standard k-ε model. The validation is performed using two selected trials of the MUST experiment under neutral conditions. Special emphasis is given on the selection of the constant value of the concentration fluctuation dissipation time scale when the k-ε model is used. Also, an intercomparison of the results between the two turbulence models is performed with a view to identifying model strengths and limitations.
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- "Formulation of the peak time-averaged concentration equation Following Bartzis et al., (2007) "
ABSTRACT: Abstract: The concentrations fluctuations of a dispersing hazardous gaseous pollutant in the atmospheric boundary layer, and the hazard associated with short-term concentration levels, demonstrate the necessity of estimating the magnitude of these fluctuations using predicting models. Moreover the computation of concentration fluctuations and individual exposure in case of dispersion in realistic situations, such as built-up areas or street canyons, is of special practical interest for hazard assessment purposes. In order to predict or/and estimate the maximum expected dosage and the exposure time within which the dosage exceeds certain health limits, the knowledge of the behaviour of concentration fluctuations at the point under consideration is needed. In this study the whole effort is based on the ‘Mock Urban Setting Test – MUST’, an extensive field test carried out on a test site of the US Army in the Great Basin Desert in 2001 (Biltoft, 2001; Yee, 2004). The experimental data that was used for the model evaluation concerned the dispersion of a passive gas between street canyons which have been created by 120 standard size shipping containers. The computational simulations have been performed using the laboratory CFD code ADREA, which has been developed for simulating the dispersion and exposure of pollutants over complex geometries. The ADREA model is evaluated by comparing the model’s predictions with the observations utilizing statistical metrics and scatter plots. The present study has been performed in the frame of the Action COST 732 “Quality Assurance and Improvement of Micro-Scale Meteorological Models”.
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ABSTRACT: One of the key problems in coping with deliberate or accidental atmospheric releases is the ability to reliably predict the individual exposure during the event. Due to the stochastic nature of turbulence, the instantaneous wind field at the time of the release is practically unknown. Therefore for consequence assessment and countermeasures application, it is more realistic to rely on maximum expected dosage rather than actual one. Recently Bartzis et al. (2007), have inaugurated an approach relating maximum dosage as a function of the exposure time, concentration mean and variance and the turbulence integral time scale. Such approaches broaden the capability of the prediction models such as CFD models to estimate maximum individual exposure at any time interval. In the present work a further insight is given to this methodology and an alternative correlation is proposed based on theoretical considerations. The methodology to utilize such correlation types is further justified.
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