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Validation of an EDP assisted model for assessing inhalation exposure and dermal exposure during spraying processes

Cover of the report "Validation of an EDP assisted model for assessing inhalation exposure and dermal exposure during spraying processes"

Software tools are increasingly used to assess the exposure of workers to hazardous substances. The absorbed dose is estimated on the basis of diverse models. For inhalation exposure and dermal exposure to non-evaporating substances applied by means of spraying processes, the deterministic model SprayExpo was revised, thoroughly tested, and compared to the existing models ConsExpo and BG-Spray in this research work. To this end, SprayExpo was validated with measurement results from real workplaces in the fields of antifouling and stored product protection.

An improved droplet impaction module for calculating the overspray during spraying onto a surface was incorporated into the SprayExpo model. Furthermore, it is no longer necessary to directly enter primary droplet distributions. Instead, for common spraying techniques these are stored in a database from which they can be retrieved by specifying the spraying technique and simple process parameters such as the spraying pressure. The sensitivity analysis revealed that besides the active substance release rate, the droplet spectrum is the decisive process parameter for the exposure. In contrast, the vapor pressure of the solvent only plays a secondary role for the exposure concentration of the active ingredient within the relevant range of values. To validate the SprayExpo model, exposure concentrations of the active substances used were determined at workplaces in the area of antifouling treatment and in several scenarios in stored product protection by personal sampling and subsequent chemical analysis. For both room spraying and spraying onto walls, comparisons between the model and experiments revealed that spray applications can generally be reproduced with an uncertainty factor of less than 4. As regards the dermal exposure, the model can only take into account the sedimentation flow of the airborne droplets, but not accidentally occurring splashes. Therefore, the dermal exposure at the workplace is underestimated by SprayExpo in the majority of cases. However, the dermal exposure is represented quite well in the case of room spraying. Based on the measured scenarios, three standard exposure scenarios were defined and documented in corresponding "fact sheets".

All in all, SprayExpo is an appropriate system for assessing exposure during indoor spraying processes. However, the fact that all models have their advantages and disadvantages should be taken into consideration. Therefore, the models have to be used reasonably and with the required expert knowledge.

MS Excel worksheet for SprayExpo 2.2

To facilitate the use of the SprayExpo model an MS Excel worksheet was developed that can be executed under Microsoft Excel 2003 or later using Microsoft Windows 2000 Service Pack 3 or later, or Windows XP or later (recommended). The main input parameters are: the released droplet spectrum, the release rate, the concentration of the active substance, the spatial and temporal pattern of the release process, the vapor pressure of the liquid, the size of the room and the ventilation rate. The path of the sprayer can be explicitly included into the model. For surface treatment by spraying, a droplet deposition module is incorporated in the programme package. This module calculates the fraction of non-impacting droplets which are relevant for human exposure.

The corresponding improved and updated software (MS Excel worksheet) for the deterministic model (SprayExpo) as well as the documentation and installation instructions can be downloaded here:
Prediction of aerosol exposure during spray application with the mechanistic model SprayExpo

W. Koch, W. Behnke, E. Berger-Preiß, H. Kock, S. Gerling, S. Hahn, K. Schröder:
Validation of an EDP assisted model for assessing inhalation exposure and dermal exposure during spraying processes. 
1. edition. Dortmund: Bundesanstalt für Arbeitsschutz und Arbeitsmedizin 2012. pp. 115, Project number: F 2137, pdf file
link to document (PDF file, 1 MB)

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