ISO 16258-2:2015 specifies the analysis of RCS in samples of air collected on collection substrates (i.e. filters or foams) by X-ray diffraction, when using an analytical approach where dust from the sample collection substrate (i.e. filter or foam) is recovered, treated and deposited on another filter for analysis by the instrument. This part of ISO 16258 includes information on the instrumental parameters, sensitivity of different sampling apparatus, the use of different filters, sample treatment to remove interference and correction for absorption effects. In this part of ISO 16258, the expression respirable crystalline silica includes the most common polymorphs quartz and cristobalite. The less common polymorphs of crystalline silica, such as tridymite, are not included within the scope of this part of ISO 16258 because a standard reference material is not available. Under certain circumstances (i.e. low filter dust loads, low silica content), the analytical approach described in this method may not fulfil the expanded uncertainty requirements of EN 482[7]. Guidance for calculation of uncertainty for measurements of RCS is given in ISO 24095.