Atmospheric dust definition

Threshold lamit Value - The term refers to toxicity by inhalation. The abbreviation used is TLV. The TLV is usually expressed in units of parts per million (ppm) - i.e., the parts of vapor (gas) per million parts of contaminated air by volume at 25 °C (77°F) and atmospheric pressure. For chemicals that form a fine mist or dust, the concentration is given in milligrams per cubic meter (mg/m ). The TLV is defined as the concentration of the chemical in air that can be breathed for five consecutive eight-hour workdays (i.e., 40 hours per week) by most people without suffering adverse health effiects. This is the definition given by the American Conference of Governmental Industrial Hygienists. 

The definition of the Maximale Arbeitsplatzkonzentration MAK (maximum workplace concentration) is the highest tolerable concentration of a chemical as gas, vapor or dust in the atmosphere at a workplace to which an employee can be exposed (using the best current knowledge) without any adverse effects on the health of an individual employee within a normal 8-hour period based on an average working week of 40 hours. The fundamental exposition schemes are based on the operative mechanism of the substance, on scientific criteria for health protection, and practical experience, rather than on technical and economic feasibility. 

Coal Mines, Determination of Firedamp and of Coal Dust In Atmospheres of. Although many instruments have been designed to detect the presence of firedamp (or rather methane) in mine atmospheres, the principles of the flame safety lamp (Davy-type lamp) still form the basis of many detectors. The Davy lamp invented in 1815 is briefly described under COAL MINE EXPLOSIONS AND FIRES and it is stated that each US mine should have at least two Davy-type lamps to serve as detectors of firedamp or of lack of oxygen. If firedamp is present in small quantity, the flame of Davy lamp elongates and if the gas is present in considerable quantity, the lamp becomes filled with blue flame. For more definite detection of gas, the flame of the lamp is lowered until the yel part is at a minimum. Then the gas will be discernible as a small blue cap over the flame. This method is described in Refs 1, 9, 12 25. Some investigators consider that the safety lamp method of detection of firedamp is not very reliable (Ref 7)... 

The continuous vaporization of cosmic dust in the upper atmosphere leads to permanent metal atom layers at altitudes between 90-100 km. As pointed out in the introduction, the metals play an important role in the lower regions of the ionospheric region (see Fig. 2). The first manifestation of upper atmospheric metals was noticed early this century, when coarse spectra of the night sky revealed a line at 589.2 nm. In 1929, Slipher suggested that this emission line was due to sodium.Later studies refined the measurement to 589.3 nm, and tne identification of the Na-D emission line was definitely made. Shortly after, the first association of the Na-D line emissions in the nightglow with meteors entering the Earth s atmosphere was made by a number of authors.The actual chemical mechanism that can lead to optical emission of the Na-D line was first suggested by Chapman" ... 

Solid bodies of extraterrestrial material that penetrate the atmosphere and reach the Earth s surface are called meteorites. Other extraterrestrial materials include micrometer-sized interplanetary dust particles (IDEs) collected in the lower stratosphere and polar ices. Most meteorites and IDEs are fragments of asteroids, but some IDEs may represent cometary material and some meteorites are fragments of the planets Mars and Earth s moon. Meteorites recovered following observed falls are called/a// those which cannot definitely be associated with observed falls are called finds. Meteorites are given names based on the location where they were recovered (e.g., the Allende meteorite fell in Allende, Mexico). Meteorites recovered in Antarctica and the deserts of Australia and northern Africa are given names and numbers, because numerous samples are found in the same locations. Fragments thought to be of the same meteorite fall, which, in Antarctica or hot deserts, may have different numbers or even names because they were found in different locations, are called... 

The aerial transport of pollen and microorganisms has received some attention (Gregory, 1973, 1978 R. Campbell, 1977). Bacteria (size < 1 p.m) are difficult to discern directly, and their study requires cultural growth techniques. In contrast to fungi spores, they usually occur attached to other aerosol particles because they are mobilized together with dust. Concentrations number several hundred per cubic meter in rural areas and several thousand in the cities. Air is not their natural habitat, so that multiplication does not take place. On the contrary, the atmospheric aerosol appears to have definite germicidal qualities (Riiden and Thofern, 1976 Riiden et al., 1978). 

Note that, under the Protection of Workers Potentially at Risk from Explosive Atmospheres Directive, there is an attempt to align the zone definitions for gases and dust clouds according to the risk of the hazard being present. Thus, there are three new zone definitions relating to dust ... 

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