ISO 23328-1:2003 gives a short-term airborne sodium chloride particle challenge test method for assessing the filtration performance of breathing system filters (BSF) intended for the filtration of respired gases. ISO 23328-1:2003 is applicable to BSF used with a clinical breathing system. It is not applicable to other types of filter, e.g. those designed to protect vacuum sources or gas sample lines, to filter compressed gases, or to protect test equipment for physiological respiratory measurements. Non-filtration aspects of BSF are addressed in ISO 23328-2.