Contamination from dust particles

An environment free from atmospheric contamination is generically called a clean room . However, clean is a relative concept, as are cold or small, and a clean room is not an environment absolutely free from dust particles. As 90% of the airborne particles have a size smaller than 0.5 pm, clean rooms are classified according to the maximal number of particles bigger than 0.5 pm... 

Redipacs are produced under GMP conditions. They are practically free from dust particles and have a good microbiological quality after production. Redipacs are not supplied sterile. When the preparation cannot be sterilised in the Redipacs, the Redipacs should be sterilised empty before use. When the Redipacs have become contaminated with dust particles, for example during pre-process handling, they should be flushed several times with purified water and dried if they are not immediately filled. 

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. 

Secondary air contamination is caused because pesticides on plant and soil surfaces convert into steam, or disperse by adsorbing on dust particles. Under certain conditions, up to 50% of such OCRs (organochlorine pesticides) as DDT, aldrin, and dieldrin move into the air during the week after a field is treated. DDT evaporates from a treated field at a rate of 10-50 kg/ha a year, depending on temperature, humidity, and air movement [3]. On the second or third day after treatment, OPP concentrations can be higher than on the first day as a result of pesticides converting into steam [22]. 

The number of scientific articles published on meteorites has increased dramatically in the last few years few of these, however, concern themselves with small meteorites, the size of which lies between that of the normal meteorites (from centimetres to metres in size) and that of interplanetary dust particles. In the course of an Antarctic expedition, scientists (mainly from French institutions) collected micrometeorites from 100 tons of Antarctic blue ice (Maurette et al 1991). These micrometeorites were only 100 400 pm in size five samples, each consisting of 30-35 particles, were studied to determine the amount of the extraterrestrial amino acids a-aminoisobutyric acid (AIBS) and isovaline—both of which are extremely rare on Earth—which they contained. The analysis was carried out using a well-tested and extremely sensitive HPLC system at the Scripps Institute, La Jolla. Although the micrometeorites came from an extremely clean environment, the samples must have been contaminated, as they all showed traces of L-amino acids. Only one sample showed a significantly higher concentration of AIBS (about 280 ppm). The AIBS/isovaline ratio in the samples also lay considerably above that previously found in CM-chondrites. 

The high sensitivity of modem instrumental techniques such as ICP-MS (Chapter 9) means that in many cases only small samples (typically, a hundred milligrams or less) need be taken for destructive analysis. However, this also means that the amounts of some individual elements may be very low, and problems of contamination can be significant. Common external contaminants include A1 from deodorants, Pb from paint or car exhausts, Zn from skin particles (and therefore from dust), and Na from sweat. The levels of contamination for each batch of samples will be revealed by the sample... 

If the perturbations are in the form of spikes of an irregular nature, the problem is likely to be detector contamination. Such spikes are especially observed when dust particles have settled into the FID flame orifice. Of course, the problem may also be due to interference from electrical pulses from some other source nearby. Regular spikes can be due to condensation in the flow lines causing the carrier, or hydrogen (FID), to pulse, or they can be due to a bubble flow meter attached to the outlet of the TCD, as well as the electrical pulses referred to above. Baseline perturbations can also be caused by pulses in the carrier flow due to a faulty flow valve or pressure regulator. 

The air coming from the tower will be carrying dust particles that must be scrubbed, thus generating a wastewater stream. The spray towers are periodically shut down and cleaned. The tower walls are scraped and thoroughly washed down. The final step is mandatory because the manufacturers must be careful to avoid contamination to the subsequent formulation. 

Contaminated soil is fed into a rotary dryer where the temperature is raised to between 500 and 800°F. As the soil is heated, moisture and volatile organic compounds (VOCs) are vaporized. The heated exhaust gases from the dryer are forced through a baghouse where soil fines and dust particles are removed. Exhaust gases are then passed through a catalytic oxidizer to remove hydrocarbons. 

Cells may become contaminated as a result of evaporation of solvent from solutions, and also by acquiring a film of grease as a result of careless handling. Such films and dust particles decrease transmission and can also contaminate liquids placed subsequently in the cell. Immediately after use therefore cells must be emptied and rinsed with clean solvent and then cleaned with a suitable detergent solution and stored in distilled water. A brush which might scratch the optical surface should never be used. Solid contaminants must always be removed by the following wet cleaning procedure ... 

Many processes are operative in the environment that contribute to the regional elimination of a contaminant by altering its distribution. Contaminants with sufficiently high vapor pressure can evaporate from contaminated terrestrial or aquatic compartments and be transferred through the atmosphere to new locations. Such processes of global distillation are considered largely responsible for the worldwide distribution of relatively volatile organochlorine pesticides such as lindane and hexachlorobenzene. Entrainment by wind and upper atmospheric currents of contaminant particles or dust onto which the contaminants are sorbed also contribute to contaminant redistribution. Sorption of contaminant to suspended solids in an aquatic environment with commensurate sedimentation can result with the removal of contaminants from the water... 

Cyclone a device for extracting dust from industrial waste gases. It is in the form of an inverted cone into which the contaminated gas enters tangential from the top the gas is propelled down a helical pathway, and the dust particles are deposited by means of centrifugal force onto the wall of the scrubber. 

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersions of aerosol occur from time to time. Following combustion of Pu metal chips in a production area at Rocky Flats, Colorado, in 1964, airborne contamination was widespread. Alpha tracks from individual particles caught on membrane filters were detected on nuclear film, and the Pu content, and hence the particle size, was deduced (Fig. 5.2, curve E). The activity median diameter was 0.3 /urn (Mann Kirchner, 1967). The same method, used during normal operations in a production area at Los Alamos, gave activity median diameters in the range 0.15 to 0.65 /urn (Moss et al., 1961). However, when a spill occurred, followed by clean-up operations, the Pu particles were found to be associated with inert dust particles of mass median diameter 7 /urn. 

Air quality in homes and workplaces is affected by human activities, construction material, underground minerals, and outside pollution. The most common indoor pollutants are radon, carbon oxides, nitrogen oxides, tobacco smoke, formaldehyde, and a large variety of organic compounds. Indoor atmospheres can also be contaminated with fine particles such as dust, aerosols (from spray cans), fungal spores, and other microorganisms. 

A second major health risk is the abundance of pesticide-laden dust particles. Since the 1960s, Uzbek cotton farmers have drained their fields into the Amu Darya and Syr Darya waterways. These giant rivers have for decades carried pesticides from the cotton fields, towards the Aral Sea where they accumulate in the soil. Strong winds then collect the pesticide contaminated dust particles... 

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