Particles, airborne

Two advantages of foam systems over sprays (qv) are the increased control of the area to which the product is deUvered and the decreased incidence of airborne particle release. 

Entrainment of Particles in an Air Stream. The lighter the particle and the finer its size, the longer it may remain suspended in an airstream such as upon filling of a bin. Secondary air currents can carry airborne particles away from a fill point into outer areas of a bin, scattering them in a way that bears no resemblance to the calculated trajectory. 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

Airborne Particles, Committee on Medical and Biological Effects of Environmental Pollutants, National Research Council, University Book Press, Baltimore, Md., 1979. 

Receptor Models. Receptor models, by their formulation, are effective in determining the contributions of various sources to particulate matter concentrations. In classic studies, sources contributing to airborne particle loadings have been identified in Washington, D.C. (78), St. Louis (9,24), Los Angeles (7,12), Portiand, Oregon (78), and Boston (79—81), as well as other areas including the desert (82). 

Barium metal and most barium compounds are highly poisonous. A notable exception is barium sulfate which is nontoxic because of its extreme iasolubihty ia water. Barium ion acts as a muscle stimulant and can cause death through ventricular fibrillation of the heart. Therefore, care must be taken to avoid contact with open areas of the skin. Workers must wear respirators (of type approved for toxic airborne particles), goggles, gloves, and protective clothing at all times. The toxic barium aluminate residue obtained from barium production is detoxified by reaction with a solution of ferrous sulfate and converted iato nontoxic barium sulfate. According to OSHA standards, the TWA value for Ba and Ba compounds ia air is 0.5 mg/m. ... 

Toxicity concerns regarding beryUium result principally from possible consequences from inbaling its oxide. Any operation that produces airborne particles or dust of the oxide must be carried out using proper precautions to personnel. 

Small airborne particles of partially burnt carbonaceous materials from smoke, which is often made more opaque by steam from combustion or from water added to the fire, may be formed when there is only partial combustion of fuel. 

These are an itnprovised version of a totally enclosed motor to protect its live parts from ingress of water, rain, snow or airborne particles etc. This is achieved by providing them with additional protection such as labyrinths at joints such as bearing end covers, centrifugal discs, end shields and terminal box and giving the outer... 

National Research Council, Airborne Particles." University Park Press, Baltimore, MD, 1979. 

Cadle, R. D., "The Measurement of Airborne Particles." Academic Press, New York, 1976. 

The chemical composition of particulate pollutants is determined in two forms specific elements, or specific compounds or ions. Knowledge of their chemical composition is useful in determining the sources of airborne particles and in understanding the fate of particles in the atmosphere. Elemental analysis yields results in terms of the individual elements present in a sample such as a given quantity of sulfur, S. From elemental analysis techniques we do not obtain direct information about the chemical form of S in a sample such as sulfate (SO/ ) or sulfide. Two nondestructive techniques used for direct elemental analysis of particulate samples are X-ray fluorescence spectroscopy (XRF) and neutron activation analysis (NAA). 

Other measurements important to visual air quality are pollutant related, i.e., the size distribution, mass concentration, and number concentration of airborne particles and their chemical composition. From the size distribution, the Mie theory of light scattering can be used to calculate the scattering coefficient (20). Table 14-2 summarizes the different types of visual monitoring methods (21). 

For larger motors, the next degree of protection is weather-protected, Type I (WPI), which is an open machine with ventilating passages con-stnicted to minimize the entrance of rain, snow, and airborne particles (o the electric parts. 

Airborne particles with diameters less than 1 micron, as in the case of asbestos, are potentially respirable therefore, the manufacture of all submicron diameter carbon particles includes a responsibility to ensure that no health hazards arc... 

MDHS 82 The dust lamp - A simple tool for observing the presence of airborne particles... 

Mean airflow velocities approach zero as the inspired airstream enters the lung parenchyma, so particle momentum also approaches zero. Most of the particles reaching the parenchyma, however, are extremely fine (< 0.5 pm MMAD), and particle buoyancy counteracts gravitational forces. Temperature gradients do not exist between the airstream and airway wall because the inspired airstream has been warmed to body temperature and fully saturated before reaching the parenchyma. Consequently, diffusion driven by Brownian motion is the only deposition mechanism remaining for airborne particles. Diffusivity, can be described under these conditions by... 

Hinds, W. C. (1999). Aerosol Technology Properties, Behavior, and Measurement of Airborne Particles (2nd ed.). John Wiley Sons, New York. 

Submicrometric particle Airborne particle with a diameter less than one... 

HSE. The Dust Lamp—A Simple Tool for Observing the Presence of Airborne Particles. MDHS 82. London HMSO, 1997. 

S. Murakami, S. Kato, S. Nagano, Y. Tanaka. Diffusion characteristics of airborne particles with gravitational settling in a convective-dominant indoor flow field. ASHRAE Transactions. 98(1), 1992, 82-97. 

The electrostatic force is directly proportional to the net charge of an aerosol particle. Therefore, effective charging of the particles is of great importance. Airborne particles are normally charged either due to their birth processes or due to charge transfer from gas ions to particles. The natural charging of particles is normally so weak that it has no practical importance for electrostatic air cleaning. 

Primary A filter that removes airborne particles 5 pm and larger, normally supplied in panel types. 

Optical particle counter An optical-electronic instrument for measuring the numbei" of airborne particles in different size ranges. 

Total airborne particles All the particles surrounded by air in a given volume of air. 

The presence of the electrolyte is required to provide a pathway for the current and, in urban areas, this is commonly ironfll) sulfate formed as a result of attack by atmospheric SO2 but, in seaside areas, airborne particles of salt are important. Because of its electrochemical nature, rusting may continue for long periods at a more or less constant rate, in contrast to the formation of an anhydrous oxide coating which under dry conditions slows down rapidly as the coating thickens. 

In the context of industrial compressors, dust is a major consideration. Such compressors have a very high throughput of air, and even in apparently clean atmospheres, the quantity of airborne dirt is sufficient to cause trouble if the compressor is not fitted with an air-intake filter. Many of the airborne particles in an industrial atmosphere are abrasive, and they cause accelerated rates of wear in any compressor with sliding components in the compressor chamber. The dirt passes into the oil, where it may accumulate and contribute very seriously to the carbon deposits in valves and outlet pipes. Another consideration is that dirt in oil is likely to act as a catalyst, thus encouraging oxidation. 

Other airborne particles These are also divisible into two groups. Firstly, the inert non-absorbent particles, usually siliceous, which can only affect corrosion by facilitating difl erential aeration processes at points of contact. 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Evaporation at 20°C is negligible a harmful concentration of airborne particles can, however, be reached quickly when dispersed. 

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