This part of ISO 14644 defines the classification system for cleanliness of surfaces in cleanrooms with regard to the presence of chemical compounds or elements (including molecules, ions, atoms and particles). This part of ISO 14644 is applicable to all solid surfaces in cleanrooms and associated controlled environments such as walls, ceilings, floors, working environment, tools, equipment and devices. NOTE 1 For the purpose of this part of ISO 14644, consideration is only given to the chemical characteristics of a particle. The physical properties of the particle are not considered and this part of ISO 14644 does not cover the interaction between the contamination and the surface. NOTE 2 This part of ISO 14644 does not include the contamination generation process and any time-dependent influences (deposition, sedimentation, ageing, etc.) or process-dependent activities such as transportation and handling. Neither does it include guidance on statistical quality control techniques to ensure compliance.