Filter selection contamination levels

Two types of sampling monitors are in general use air samples are used to assess the airborne contamination levels at selected points. In the case of particulate materials a volume of air is drawn through a filter paper on which the particulates are deposited. An alarm may be set on increase of activity. 

The critical applications in the electronics industry are the production of ultra-pure water for the washing of semi-conductor material (silicon chips), and the cleaning of the chemical fluids (liquid and gaseous) used in their manufacture. The object of an ultra-pure water plant for semi-conductor manufacture is to produce water as close to the theoretical purity as possible. Users of ultra-pure water should take all steps possible to ensure that the filters selected meet the highest standards of quality and performance. Every fluid that comes into contact with integrated circuit surfaces is a potential sonrce of the contamination that will affect yields. For this reason, filtration of these fluids at the point of use is essential to obtain high yields. All chemicals that contact microcircuits should be filtered to a level of at least 0.2 pm. 

Once a required cleanliness range has been determined, to which a hydrauhc system reliability can be directly related, the final task is to select correct cost-effective filters that retain the contamination level balance in the system, i.e. the total number of particles generated in the system is equal to (or less than) the total number of particles removed. 

The modification of silica gel with diethanolamine (DEA) resulted in a stable alkaline filter, capable to collect H2S, COS, CS2, S02, C02 and H20 from contaminated air.56 The presence of odorous mercaptanes and organic sulphides may be selectively determined, as these compounds do not react with the DEA and therefore are not collected on the filter. By means of this scrubber an automatic survey system has been developed allowing the detection and determination of the nature of odour nuisance, caused by industrial emissions of volatile organic sulphur compounds, up to the ppb-level. The system consists of two continuous, highly sensitive and fast responding sulphur analyzers. One of the detectors is equipped with an SO, scrubber and measures the total amount of non-S02 sulphur compounds. The other detects the organic S-compounds, using the amine-silica filter. 

The GC detector is the last major instrument component to discuss. The GC detector appears in Fig. 4.7 as the box to which the column outlet is connected. Evolution in GC detector technology has been as great as any other component of the gas chromatograph during the past 40 years. Among all GC detectors, the photoionization (PID), electrolytic conductivity (EICD), electron-capture (ECD), and mass selective detector (MSD) (or quadrupole mass filter) have been the most important to TEQA. The fact that an environmental contaminant can be measured in some cases down to concentration levels of parts per trillion (ppt) is a direct tribute to the success of these very sensitive GC detectors and to advances in electronic amplifier design. GC detectors manufactured during the packed column era were found to be compatible with WCOTs. In some cases, makeup gas must be introduced, such as for the ECD. Before we discuss these GC detectors and their importance to TEQA, let us list the most common commercially available GC detectors and then classify these detectors from several points of view. 

The selection of respirator is based on the nature of respiratory hazards such as permissible exposure limits, established concentration immediately dangerous to life, actual concentration of hazardous substances, and amount of oxygen. When using filters, the ambient air must contain at least 20% oxygen at sea level. Filter protection should not be used for unknown contaminants and contaminants fliat are immediately dangerous to life and health. 

When employee exposure is identified, the employer can consider the respirators Assigned Protection Factors (APFs). The APFs are used to select equipment that will meet or exceed the required level of filter to protect the employee from the hazardous contaminant. 

Owing to the relatively high levels of zinc found in most of the biological mediums, contamination of the samples from stainless steel needles, tubes, instmments, and containers need not be feared if the samples are taken with care [58]. For selecting adequate materials, the reader is referred to the book of Van Loon [59], who examined the levels of impurities in various plastics, glasses, tubes, and filters. 

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