Particulate, contamination

Trees originating at a shield—insulation interface are mosdy due to the existence of protmsion from the shields. They are referred to as vented trees if moisture is present, they are called vented water trees. Particulate contaminants present in the insulation, and waterborne ionizable materials that find their way into the insulation, are also causes of tree formation. 

Electrodialysis. Electro dialysis processes transfer ions of dissolved salts across membranes, leaving purified water behind. Ion movement is induced by direct current electrical fields. A negative electrode (cathode) attracts cations, and a positive electrode (anode) attracts anions. Systems are compartmentalized in stacks by alternating cation and anion transfer membranes. Alternating compartments carry concentrated brine and purified permeate. Typically, 40—60% of dissolved ions are removed or rejected. Further improvement in water quaUty is obtained by staging (operation of stacks in series). ED processes do not remove particulate contaminants or weakly ionized contaminants, such as siUca. 

To meet the cleanliness need, all elements of the process are controlled to minimize sources of contamination. Air normally contains a large volume of contaminants in the form of dirt, dust, and poUen. The human body sheds a large volume of particulate contaminants such as skin, phlegm, hair, etc. 

High-efficiency air filters are sometimes used for emission control when particulate contaminants are low in concentration but present special hazards cleaning of ventilation air and other gas streams exhausted from nuclear ant operations is an example. 

The atmospheric fate of contaminants must be assessed whenever it is determined that significant gaseous or airborne particulate contaminants are released from the site. The atmospheric fate of contaminants released originally to other media, but eventually partitioned to the atmosphere beyond site boundaries, must also be assessed whenever this intermedia transfer is likely to be significant. 

Settling and rainout are important mechanisms of contaminant transfer from the atmospheric media to both surface soils and surface waters. Rates of contaminant transfer caused by these mechanisms are difficult to assess qualitatively however, they increase with increasing soil adsorption coefficients, solubility (for particulate contaminants or those adsorbed to particles), particle size, and precipitation frequency. 

The water is then pumped through series operated sand filters, which provide the final stage of suspended solids removal and protect the garnualr activated carbon (GAC) filters from particulate contamination. Series operated GAC filters are then used to remove the dissolved creosote and pesticides from the water. To achieve compliance with specifications levels, water should be sampled and analyzed after leaving the first GAC filter. The second GAC filter normally serves as a guard bed. 

Among the major potential hazards affecting working environment are chemical (airborne contaminants), biological, and physical hazards,. ir contaminants are commonly classified as either particulate contaminants or gas and vapor contaminants. Common particulate contaminants include dusts, fumes, mists, aerosols, and fibers. 

The purpose of open unidirectional airflow benches is to protect products from particulate contaminants by creating a controlled environment. These benches are used, for example, in electronic, biological, pharmaceutical, and food industries. It should be mentioned that within pharmaceutical production, aseptic sterile processes must be carried out in a Class 100 environment (U.S. Federal Standard 209 E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones). To avoid particle contamination in the bench, horizontal or vertical airflow with high-efficiency particulate air (HEPA)-filtered air is used. The air velocity is normally 0.4-0.5 ra s". Some examples of typical arrangements of open unidirectional airflow benches are shown in Fig. 10.51. 

One of the oldest, simplest, and most efficient methods for removing solid particulate contaminants from gas streams is by filtration through fabric media. The fabric filter is capable of providing high collection efficiencies for particles as small as 0.5 pm and will remove a substantial quantity of particles as small as 0.01 pm. In its simplest form, the industrial fabric filter consists of a woven or felted fabric through which dust-laden gases are forced. A combination of factors results in the collection of particles on the fabric filters. When woven fabrics arc used, a dust cake eventually forms. This, in turn, acts predominantly as a sieving mechanism. When felted fabrics are used, the dust cake is minimal or nonc.xistent. 

Hydraulic fluid contamination may be described as any foreign material or substance whose presence in the fluid is capable of adversely affecting system performance or reliability. It may assume many different forms, including liquids, gases, and solid matter of various composition, sizes, and shapes. Solid matter is the type most often found in hydraulic systems and is generally referred to as particulate contamination. Contamination is always present to some degree, even in new, unused fluid, but must be kept below a level that will adversely affect system operation. Hydraulic contamination control consists of requirements, techniques, and practices necessary to minimize and control fluid contamination. 

Particulate contamination This class of contaminants includes organic, metallic solid, and inorganic solid contaminants. These contaminants are discussed in the following paragraphs. 

Excessive particulate contamination of the fluid indicates that the filters are not keeping the system clean. This can result from improper filter maintenance, inadequate filters, or excessive ongoing corrosion and wear. 

Normal spectrographic analysis is limited to particulate contamination with a size of 10 microns or less. Larger contaminants are ignored. This fact can limit the benefits that can be derived from the technique. 

The second difference is that particulate contamination larger than 10 microns can be separated and analyzed. Normal ferrographic analysis will capture particles up to 100 microns and provides a better representation of the total oil contamination than spectrographic techniques. 

Oil-related analysis encompasses a variety of physical and chemical tests such as viscosity, total acid number and particulate contamination. This is often extended to include the identification of wear debris, as an early warning of component failure, by either spectrographic... 

Deposition is the atmospheric removal process by which gaseous and particulate contaminants are transferred from the atmosphere to surface receptors - soil, vegetation, and surface waters (22,27,28, 32). This process has been conveniently separated into two categories dry and wet deposition. Dry deposition is a direct transfer process that removes contaminants from the atmosphere without the intervention of precipitation, and therefore may occur continuously. Wet deposition involves the removal of contaminants from the atmosphere in an aqueous form and is therefore dependent on the precipitation events of rain, snow, or fog. 

Dust and fume masks consist of one or two cartridges containing a suitable filter (e.g. paper or resin-impregnated wool) to remove particulate contaminant. The efficiency of the filters against particles of various sizes is quoted in manufacturers literature and national standards. Such masks do not remove vapour from the air. 

Fiber means any particulate contaminant with a length at least three times greater than its width. 

Particulate contamination Microbial contamination and sterility (in the unopened container and under conditions of use)... 

The significance of particulate contamination in all parenteral preparations and devices has received much attention. Although it has not been established that particles can cause toxic effects, the pharmaceutical industry, the medical profession, hospital pharmacists, and FDA all realize the importance of reducing particulate levels in all parenteral products and devices. 

Rank the following polypropylene conversion processes in terms of their relative sensitivity to particulate contamination, film casting, injection molding or fiber spinning. 

As expected, the EDS data set indicates that the polymeric matrix material (the PE-PP blend) is composed only of carbon (hydrogen is not detectable by this method). The particle, however, appears to be composed mainly of aluminum and oxygen along with small amounts of copper. The ratio of aluminum to oxygen is consistent with the chemical formula for aluminum oxide (A1203). The SEM-EDS results are consistent with aluminum oxide and traces of copper as the primary constituents of the particulate contamination. (Al2O3.3H20 is a commonly used fire-retardant additive in polymeric products.)... 

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