Gases exposure, definition

Chlorine (CI2) is one of the more commonly produced ehemieals in the USA, and ehlorine gas is a potent oxidant whieh is very irritating and, potentially, corrosive (Kikilo et ah, 2008 Smith et ah, 2008 Wismer, 2007). Chlorine gas is used as a pulmonary and ehoking agent, and exposure is frequently assoeiated moderate to severe, painful irritation of the eyes and respiratory traet (Wismer, 2007). Such stressful, sublethal exposures in late-gestational women or animals might be expeeted to be associated with the induetion of premature parturition and, possibly, abortion. Oxidative stress ean definitely have adverse effects on reproductive funetion, but the chronic disease usually assoeiated with ehlorine gas exposure is primarily related to... 

Low in threshold of action. Thus, mustard gas protiuces definite ineapAeitating effeets in concentrations as low as 1 100,000 (0.0065 nig. jier liter) with 60 minutes exposure, and on longer exposure equal reaulte are obtained with proportionately lower concentrations. 

Debye has developed a theory for evaluating gas exposures which, for given atomic coordinates, represents the intensity of the scattered beam as a function of the angle of diffraction. It is obviously not possible in general to deduce a definite molecular model from one experimental diagram without further assumptions (harmonic analysis). Frequently the evaluation of the diffraction pattern must be based on a tentatively assumed plausible model, the interferences given by it calculated and th( model compared with the diagram actually obtained. 

L exposure would produce 1 ML of adsorbates if the sticking coefficient were unity. Note that a quantitative calculation of the exposure per surface atom depends on the molecular weight of the gas molecules and on the actual density of surface atoms, but the approximations inlierent in the definition of tire Langmuir are often inconsequential. 

Several additional terms related to the absorption of x-radiation require definition energy of a x-ray photon is properly represented in joules but more conveniently reported in eV fluence is the sum of the energy in a unit area intensity or flux is the fluence per unit time and the exposure is a measure of the number of ions produced in a mass of gas. The unit of exposure in medicine is the Rn ntgen, R, defined as the quantity of radiation required to produce 2.58 x C/kg of air. The absorbed dose for a tissue is a measure of energy dissipated per unit mass. The measure of absorbed dose most... 

Two other methods worth discussing are wet air oxidation and regeneration by steam. Wet oxidation may be defined as a process in which a substance in aqueous solution or suspension is oxidized by oxygen transferred from a gas phase in intimate contact with the liquid phase. The substance may be organic or inorganic in nature. In this broad definition, both the well known oxidation of ferrous salts to ferric salts by exposure of a solution to air at room temperature and the adsorption of oxygen by alkaline pyrogallol in the classical Orsat gas analysis would be considered wet oxidations. 

Much of the initial development of Gaussian modeling and definition of dispersion paramenters was done during and after World War I in addressing the problem of poison gas dispersal. These studies involved the definition of risk factors, such as exposure and dose. The next intensive development effort came during and after World War II with the nuclear weapons program. 

Although at first sight this definition does not appear to be clinically useful, multiples of MAC are employed in clinica trials to allow doses of different inhaled agents to be standardised and the effects compared. The term MAC hours (MACxduration of exposure in hours) is widely used as a measure of total dosage over time, and is especially useful in toxicity and pollution studies. In gas mixtures, MAC values are broadly additive so that, e.g. 0.5 MAC N20 combined with 0.5 MAC isoflurane is equipotent with 1 MAC isoflurane alone. 

The remarkable variations in the viscosity of molten sulphur have already been mentioned. Definite measurements have been made at a series of temperatures by the method of rotating cylinders,5 and it, has been found that exposure of the liquid to air, especially below 160° C., has a marked effect on the viscosity from 160° C. onwards. The viscosity of purified (twice distilled but not gas-free) sulphur lias a value at 123° C. of 0 1094 C.G.S. units this falls to a minimum of 0 0709 at 150° C., rises gradually up to about 159° then rapidly increases above this temperature an exact transition point is not observed, however. The maximum for purified unexposed (gas-frcc) sulphur occurs at about 200° C. and has a value of 215 C.G.S. units. For purified (not gas-free) sulphur after prolonged exposure to the air, the maximum occurs at about 190° C, and may have a value as high as 800 C.G.S. units. Such high viscosity appears to be due to impurities, the chief being sulphuric acid, resulting from exposure to the air sulphur dioxide and ammonia in solution also have an appreciable effect. 

C is a definite quantity for each gas according to the physiological effect desired and the time of exposure to the gas. 

There is evidence that long-term phosphine exposure by individuals involved in the application of pesticides resulted in chromosome damage. Chronic exposure to very low levels of phosphine may result in altered motor, visual, and speech skills. Neither aluminum phosphide nor phosphine gas exhibit carcinogenicity in humans, or result in reproductive or developmental effects. Although definitive evidence is lacking, it is assumed that phospine is an in vivo inhibitor of oxidative phosphorylation. 

Research in the field of combustion toxicology is primarily concerned with items 1, all of which are related to the toxic potency of the fire gas effluent. Toxic potency is defined by ASTM as a quantitative expression relating concentration (of smoke or combustion gases) and exposure time to a particular degree of adverse physiological response, for example, death on exposure of humans or animals. This definition is followed by a discussion, which states, The toxic potency of smoke from any material or product or assembly is related to the composition of that smoke which, in turn, is dependent upon the conditions under which the smoke is generated. One should add that the LCso is a common end point used in laboratories to assess toxic potency. In the comparison of the toxic potencies of different compounds or materials, the lower the LC50 (i.e., the smaller the amount of material necessary to reach the toxic end point), the more toxic the material is. 

To create micromachines, films that have been deposited must be patterned and etched to reveal the desired structures. Often, it is important to etch these structures with vertical sidewalls (anisotropic etching). In this case, most pattern transfer operations (lithography and etch) are carried out using plasma etching. Conceptually, this process is the reverse of deposition. The etching process consists of exposure of the patterned and masked substrate to a low-pressure plasma. The reactive species and ions preferentially etch those areas that are not masked, resulting in the definition of features on the surface. The key to plasma etching is that the products of the reaction of the activated gas and the material to be etched must be volatile (see e.g.. Ref ). 

Many CW agents are encountered as gases. Establishing the dose of a gas is difficult compared with that provided by, say, an intravenous injection. This has led to the definition of exposure rather than dose and to the concentration x time product. Exposure may be thus measured in... 

The second edition consists of an introduction, four sections, and two appendices. (The appendices present examples and are not part of the consensus document.) Section 1 identifies the scope of the standard and section 2 lists definitions for particular terms. Thus, paraphrasing, adequate ventilation refers to a condition in which air contaminant concentrations are below levels that cause injury or illness, or, that the vapors of flammable liquids are well below the lower flammable limit. A toxic chemical has an oral LD50 for edbino rats greater than 50 mg/kg but not greater than 500 mg/kg, or a 24 hr. skin contact LD50 for albino rabbits more than 200 mg/kg but not more than 1000 mg/kg, or an inhalation LC50 for albino rats more than 200 ppm but not more than 2000 ppm of gas or vapor or more than 2 mg/f but not more than 20 mg/f of dust or mist, provided that such exposures are reasonably likely to be encountered by humans in their use of the chemical. 

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