Airborne contamination problem

Process Associated problems Hazardous airborne contaminants liberated (in addition to tbe principal reagents)... 

Airborne contamination is another possible contribution to the blank correction. Here one is chiefly concerned with sample contamination with the daughters of 222Rn, which have half-lives in the 30- to 40-min range. Steps that can be taken to avoid this problem include eschewing the use of suction filtration in chemical procedures, prefiltering of room air, and use of radon traps. 

In many cases, bypass piping is installed while a tank is being repaired or refurbished (Fig. 1). The result is no protection at all. The existence of open tanks may also be undesirable, particularly where fumes or airborne contaminants pose problems. 

When the search area is large, interest is often concentrated on determining whether or not a munitions waste contamination problem even exists. If it does exist, interest is then focused on which subareas(s) of the site is contaminated. Search precision could be sacrificed for speed detailed exploration on the ground would be conducted if a rapid surface search indicated the likelihood of munitions waste being present. There is an evident need for better, faster, and more reliable methods for surface surveys of contaminated areas or areas where contamination is only suspected. Once again, the development of platforms and instruments for aerial survey would appear to be appropriate. Airborne radar surveys of large areas may constitute a rapid and inexpensive means of locating surface munitions. Airborne infrared sensors that can detect the small temperature differences between surface metallic objects and the soil may also prove useful for this purpose. 

Tower location relative to the prevailing wind direction to minimise contamination problems from dust, gases and other airborne components that may occur. 

However, generdly measurements are not required. Priority is given to inspection activity in woi laces where actions are most likely to be need. Here it is normally not necessary to measure airborne contaminants in relation to their OELs since it will be obvious that OELs are being exceeded or there are other obvious problems that imply they will be exceeded. 

If large and heavy filters are used to maximize retention of airborne contaminants, they must be worn on the body using suitable assemblies connected to the mask by an air line. In such a case the support of a power-assisted filtering device is recommended (see Section 6.8.4.1.3). Persons using refractive lenses quite often complain about problems with low wearing comfort when using full-face masks, and they also have fogging problems with the visors. This problem does not occur with half masks. 

Contamination by airborne basic substances such as amines and N-methylpyrrolidone (NMP) has been shown to be responsible for the formation of the surface insoluble layer. Because of the catalytic nature of the imaging chemistries, a trace amount on the order of 10 ppb of airborne basic substances absorbed in the resist film interfaces with desired acid-catalyzed reactions, and also certain polymers and groups can function as internal contamination. Activated carbon filtration of the enclosing atmosphere can alleviate the contamination problem. Application of a protective... 

Special surveys may be undertaken to meet specific problems, for example, if high levels of airborne contamination or loose surface contamination are suspected, or when routine monitoring reveals unusual or abnormal conditions such as the occurrence of an area of elevated activity (also called a hot spot). 

These kinds of environmental contamination problems are everyday occurrences in the semiconductor industry because of the strict cleanliness demands required for the fabrication of silicon wafers and production of semiconductor devices. The purity of silicon wafers has a direct effect on the yield of devices, so it is crucial that trace element contamination levels are kept to a minimum in order to reduce defects. This means that any analytical methodology used to determine purity levels on the surface of silicon wafers, or in the high-purity chemicals used to mauufacture the devices, must use spotlessly clean instruments. These unique demauds of the semiconductor industry have led to the development of special air filtration systems that continually pump air through ultraclean high-efficiency particulate air (HEPA) filters to remove the majority of airborne particulates. 

You should have the proper personal protective equipment if your workforce has the potential to be exposed to airborne contaminants or spilled chemicals. You should tell your workforce what you expect them to do in case of an emergency. If they have been trained, yon might want them to help in mitigating the problem, cleanup, or containment. If you expect them to evacuate, then you need to tell them so. 

Another intriguing aspect of the methacrylate terpolymer CA resist polymers is their airborne contaminant absorption properties relative to more conventional CA resist materials (9). N-methylpyrrolidone (NMP) has been reported to result in serious image degradation of CA positive resists when present in very low levels in the air in resist processing enviromnents ilO). This is a very serious problem, as NMP is ubiquitous in IC fabrication lines, where it is used in resist stripping operations and as a solvent for polymer dielectrics... 

During construction it is impossible to avoid contamination of the piping with airborn ferrous particles from installation of structural steel and carbon steel piping components. If the stainless steel is kept dry, this may not be a problem. If the stainless steel piping is allowed to become wet, e.g., from a hydrostatic pressure test, the system should be tested with dry, oil-free air. If water is used, then provision must be made to thoroughly clean the system immediately after the hydrostatic pressure test. 

Airborne Basic Chemical Contamination. A critical, and at-first puzzling problem, was encountered during early manufacturing trials of CA resists. Sporadically, severely distorted resist profiles would be formed in positive-tone CA resists, displaying what seemed to be a cap on the upper surface of the resist image (Fig. 26). In severe cases this cap or T-top would appear as a kin or cmst over the entire wafer surface that prevented development of the pattern. The magnitude of the effect varied dramatically between laboratories and appeared to grow more severe as the time interval between exposure and post-exposure bake was increased. 

Often, many simultaneously occurring pollutants or contaminants determine an environmental problem. In industry, agriculture, and households, products are often mixtures of many compounds. The process of production and consumption is accompanied by emissions and consequently by contamination. One example is the use of toxaphene in the past, a very complex mixture of polychlorinated camphenes, as a pesticide. Technical toxaphene consists of more than 175 individual compounds. A second example is industrial and domestic emissions resulting from the combustion of fossil fuels. The emissions contain both a mixture of gases (SO2, NOx, CO2, etc.) and airborne particulate matter which itself contains a broad range of heavy metals and also polycyclic aromatic hydrocarbons (PAH). 

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]. 

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