Irrespective of the spray generation method, it is advisable to measure particle size distribution and other aerosol characteristics and their time-dependent change, including agglomeration, sedimentation, and ageing effects in order to make a thorough safety assessment. Common methods of particle size measurement include, e.g., laser diffraction, use of the cascade impactor and time of flight spectroscopy, but droplets can change
Selleck BYL719 due to ageing processes during the flight phase so care must be taken when analysing measured data. Droplet diameter may decrease by evaporation of volatile constituents. Droplets may disperse after collision with solid surfaces, they may aggregate, and deposit on solid surfaces. Therefore, any spray pattern is subject to constant changes, and the interpretation and application of any such analytical data
to the safety assessment must be carried out keeping in mind the limitations of accuracy and applicability of such data. Furthermore, the setting of product- and method-specific parameters in the establishment of such analytical methods requires great experience and well trained personnel. A detailed overview on particle size measurement methods is given in the guidance document of the European Aerosol Association FEA (FEA European Aerosol Federation, 2009). selleck chemicals To prepare a proper safety assessment for spray products the best knowledge on the inhalation exposure under intended use conditions should be available or estimated. Real time measurements of specific product exposure represent the gold standard, but need complex and extensive study designs. More simple mathematical approaches taking into account worst case defaults can be used as a first step in a tiered approach for exposure assessment. Easily, the concentration of any ingredient in the ambient air can be calculated on the basis of the worst-case estimation Chlormezanone of the applied amount, duration of application as well as the distribution volume, e.g., the volume of a standard
bath room. By using conservative defaults (see below) the calculation of the exposure will overestimate the real situation of human exposure. A clear advantage of this approach is that a safety assessment may be rapidly performed and is independent of extensive measurements. In those cases where a risk assessment on the basis of such an initial conservative procedure does not yield a sufficient safety margin, a refined exposure assessment needs to be conducted. Relevant data that reflect actual application situations may be generated by measuring aerosol concentration and particle size in a model environment (for example a standard bathroom). Reality-based mathematical models (e.g., ConsExpo 4.1 (Bremmer et al., 2006a), BG-Spray (Eickmann, 2007a)) can also be used to quantify aerosol concentrations over time.