1. Definition of cleanliness levels

Before discussing the CO ₂ pressure cleaning process, it's essential to address the notion of cleanliness. Surface contamination exists in many forms and is present in different states on the surface of a substrate. Among the most common categories are particles, thin or molecular films, organic or inorganic bodies, ionics, and bacteriological contamination. This list can be extended to metals, chemical compounds (toxic and hazardous), and radioactive or biological particles, encountered in various industrial processes such as semiconductor production, metal machining, the manufacture of polymer objects, the nuclear industry, the pharmaceutical and medical industries, or the food industry.

The most common sources of contamination include :

• machining oils and greases ;...