Contamination airborne, minimization

Three approaches have been identified that reduce susceptibility of CA resists to airborne contamination. In the first, process engineering changes such as the addition of special activated carbon filters to the environmental chambers surrounding the exposure tools (76,79), overcoating the resist with a soluble protective film to isolate the resist from the environment (77,80,81), or modifications of the process flow to minimize the time interval between exposure and post-exposure bake have been shown to improve CA resist processibibty. 

Radiation from a dirty bomb can emanate from a blast site in a contaminated plume of smoke or in contaminated debris. Radiation cannot be detected without special instruments, and radiation exposures can occur even without direct contact. Therefore, leaving a damaged building does not eliminate the risk of exposure. An effective tool to minimize or eliminate the potential for hazardous substance exposure is to move away from the site of the attack and into a building that provides protection from airborne contaminants. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

Specific regulations exist for the transport of asbestos materials by highway [53]. Asbestos must be loaded, handled, and unloaded using procedures that minimize occupational exposure to airborne asbestos particles released in association with transportation. Any asbestos contamination of transport vehicles also must be removed using such procedures (49 CFR 177.844). Additional motor carrier s safely regulations apply to common, contract, and private carriers of property by motor vehicle, as defined under these regulations (49 CFR Parts 390-397). 

ISOTRON s ELECTROSORB C technology applies an electric field to induce migration of ionic contaminants from within porous concrete. This process provides an in situ alternative to concrete decontamination, thereby eliminating physical or mechanical damage of the concrete and allowing reuse of the structure or facility. The process generates minimal secondary waste and no airborne particulates common to conventional scabbUng or physical abrasion techniques. 

Minimization of exposnre to airborne contaminants, and reduced mixing of wastes during recovery processes... 

At the current time it is recommended that 1-10 mg of solid sample be analyzed. In environments that are not heavily contaminated with airborne dust it takes several days for sample collection. In an unoccupied or minimally occupied room around lmg of dust needed for analysis can be collected in 72 h. In a heavily occupied room the levels of dust increase dramatically and collection takes around 6-8 h. 

Maintain higher air pressures (positive pressure) within the critical areas to minimize infiltration of airborne contaminants from outside air... 

Although the importance of environmental factors (temperature, rela-- -tive humidity, airborne contaminants, and oxygen) that affect the fading of dyed textiles exposed to artificial and natural light indoors is well documented (1,2), relatively little information exists on the effectiveness of UV stabilizers incorporated into plastic films to minimize or retard such fading. To obtain this information, light-sensitive blue wool fabric (AATCC L-4 standard) was exposed to light from a xenon-arc source, with and without protection by clear cellulose acetate films... 

Use chemical fume hoods or other engineering controls to minimize exposure to airborne contaminants. 

Few papers on the analysis of PCAs or their measurement in environmental samples have reported on techniques to minimize contamination. PCAs (C10-C13,60-70% Cl) levels ranging from 4 ng g 1 to 25 ngg 1 in sodium sulfate were found in procedural blanks used in sediment extractions [28]. PCAs (C10-C13,60-70% Cl) were also detected in DCM (0.15 pg 1 ) left to evaporate in an open flask overnight it was unclear, however, whether contamination was a result of airborne PCAs or was from the DCM itself [28]. Similar problems have been encountered with airborne PCB contamination of analytical labs [65]. Significant procedural blanks result in higher method detection limits, i. e., the mean plus three times the standard deviation in the background signals from procedural blanks (sodium sulfate) [14,66,67]. 

Samples were run on a Supelco LC-18-DB HPLC column, 2.1 mm X 25 cm. The buffers were A= 0.1% TFA in Milli-Q water, B= 0.09% TFA in 70% acetonitrile and the gradient was 0% B, 5min. 0 - 10% B, lOmin. 10 -50% B, 60 min. 50 - 100% B, 25 min. 100% B, lOmin. Fractions were collected in 1.5 nd polypropylene tubes, which were precleaned with 0.1% TFA in 50% acetonitrile, using an Isco Foxy fraction collector with peak separator. The fraction collector was enclosed in a Plexiglas chamber which was under positive nitrogen pressure to minimize airborne contamination of fractions. Fractions were capped and stored at -20 C. Immediately before loading on the sequencer, TFA (ABI) was added to fractions (25% final) to minimize peptide losses due to adsorption to the tube or pipet tip (18). 

World Health Organization (WHO) identify Biosafety Levels 1,2, 3, and 4 and in the United Kingdom the Advisory Committee on Dangerous Pathogens (ACDP) categorizes Laboratory Containment Levels 1, 2, 3, and 4 (4-6). All share the same objective to identify biosafety or laboratory containment levels that minimize the risk to the laboratory worker, to the outside community, and to the environment. At Biosafety/Laboratory Containment Level 2, exposure risks to the laboratory worker arise mainly from contact through a contaminated work environment. As the risk of airborne infection increases, Biosafety/ Laboratory Containment Level 3 provides facilities to prevent aerosol transmission. Additional safeguards to protect the outside community and the environment are found at Biosafety/Laboratory Containment Level 4, which is... 

Epidemiological and Human Dosimetry Studies. Results from many acute controlled-exposure human studies and cross-sectional studies of groups of persons repeatedly exposed to airborne formaldehyde provide strong evidence that the upper respiratory tract is the critical target of airborne formaldehyde for any duration of exposure, allow reasonable estimates to be made of minimal risk levels for acute and chronic durations of exposure, and provide strong support for deriving intermediate-duration minimal risk levels from animal exposure-response data. There is considerable confidence that adherence to these values will protect persons living near formaldehyde-contaminated hazardous waste... 

A third study evaluated S04 and exposure to 24 children (ages were not provided) living in Uniontown, Pennsylvania (Suh et al. 1992). This study did not focus on ammonia exposure per se, but on other airborne contaminant concentrations in aerosols found outdoors, indoors, and by personal monitors. It sought to determine how personal exposures to these aerosols correlated with indoor and outdoor concentrations. Ammonia concentrations were measured in order to assess their potential for neutralizing found in aerosols. Ammonia was found to be in highest concentrations near the children (detected by the personal monitors), followed by indoor concentrations, and were minimal outdoors. It was proposed that a large proportion of the found in indoor aerosols are neutralized by NH3, and thus would lower the children s exposure to acid aerosols. The authors noted that more research is needed to fully model the influence of factors, including NH3, on indoor acid aerosol exposure. 

Chemical amplification resists require PEB in general to accelerate acid-catalyzed reactions and thus the acid generated by irradiation could be deactivated (by airborne contamination) upon standing before PEB. Then, generation of acid when it is needed (at the time of PEB) could eliminate/minimize the... 

Silicone contamination has been implicated as a cause of failure in telephone switching systems and other devices that contain relay switch contacts (507). Analysis of airborne particulates near telephone switching stations showed the presence of silicones at these locations. Where the indoor use of silicones is intentionally minimized, outdoor levels were found to be higher than inside concentrations (508). Samples of particulates taken at two New Jersey office buildings revealed silicone levels that were considerably higher indoors than outdoors. In these cases, indoor silicone aerosols are believed to be generated primarily by photocopiers, which use silicone fuser oils. 

---