Of these microbes, only bacteria (commonly) and fungi (less commonly) have been used for remediation and removal of contaminants, ,, ,. Microbial Mergers refer to combinations and collaborations between different microbe species. These cleanliness levels are either very desirable or are required by the function of parts such as metal devices, electronic assemblies, optical and laser components, precision mechanical parts, and computer parts. In many commercial applications, the precision cleanliness level is defined as an organic contaminant level of <10 µg of contaminant/cm 2, although for many applications the requirement is set at 1 µg/cm 2. The cleanliness levels are based on contamination levels established in industry standard IEST-STD-CC1246D for particles from Level 1 to Level 1000 and for NVR from Level AA5 (0.1 ng/cm 2) to Level J (0.025 mg/cm 2). For example, civilian and defense space agencies worldwide specify surface cleanliness levels for space hardware for particles in the micrometer per unit area size range and for NVR in the microgram per square centimeter range. Typical cleaning specifications are based on the amount of specific or characteristic contaminant remaining on the surface after it has been cleaned.Ĭleanliness levels in precision technology applications are typically specified for particles, as well as for hydrocarbon contamination represented by nonvolatile residue (NVR). In addition, a whole host of other chemical contaminants from a variety of sources may soil a surface. Common contamination sources can include machining oils and greases, hydraulic and cleaning fluids, adhesives, waxes, human contamination, and particulates. Surface contamination can be in many forms and may be present in a variety of states on the surface. Other contaminant categories include metals, toxic and hazardous chemicals, radioactive materials, and biological substances that are identified for surfaces employed in specific industries. The most common categories of surface contaminants include particles, thin film or molecular contamination that can be organic or inorganic, ionic contamination, and microbial contamination. 2. Surface Contamination and Cleanliness Levels
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