Vapour concentration

Saturated vapour concentration Specific gravity Vapour density (air = 1) Solubility in water... 

AUTO-iGNiTiON TEMPERATURE The minimum temperature required to initiate or cause self-sustained combustion of material in the absence of any external source of energy. (Values may change significantly with geometry, gas/vapour concentration, and if catalyst is present.)... 

FLASH POINT The lowest temperature required to raise the vapour pressure of a liquid such that vapour concentration in air near the surface of the liquid is within the flammable range, and as such the air/vapour mixture will ignite in the presence of a suitable ignition source, usually a flame. (Open cup values are approximately 5.5° to 8.3°C higher than the closed cup values.)... 

For most chemicals, inhalation is the main route of entry into the body. However, certain chemicals (e.g. phenol, aniline, certain pesticides) can penetrate intact skin and so become absorbed into the body. This may occur through local contamination, e.g. from a liquid splash, or through exposure to high vapour concentrations. Special precautions to avoid skin contact are required with these chemicals and potential exposure via skin absorption has to be taken into account when assessing the adequacy of control measures. Chemicals able to penetrate intact skin are listed in Table 4.2. 

Pure ozone is made by fractional distillation of the blue liquid resulting from the cooling of ozonized oxygen in liquid air. Commercially it is often supplied dissolved in chlorofluorocarbons in stainless steel cylinders at ca 475 psig cylinder pressure at 20°C often transported chilled with dry ice. These solutions can be handled safely at vapour concentrations of ca 20% by volume of ozone. 

But that is not sufficient. The ability to vapourise has to be such that the vapour concentration in the air reaches a value that enables propagation of the flame into the gaseous mass from the point where the ignition occurred. If the concentration is insufficient, it is said that the mixture is too poor , or, at the other extreme, too rich . The limits of the range within which combustion is possible are called lower explosive limit (LEL) and upper expiosive limit (UEL). 

The vapour pressure of a liquid provides an essential safety parameter and it is mandatory that safety sheets contain these values (when they are known). This parameter is taken into account in some classification methods of inflammability risk. It enables one to determine the equilibrium vapour concentration of a liquid in air. This concentration can then be used to ascertain whether a working environment presents an inflammability risk (by reference to the inflammability limits) or a toxicity hazard (by comparison with the exposure values). 

Mixtures become inflammable when the vapour concentration lies between two limits called the lower explosive limit (LEL) and the upper explosive limit (UEL). These limits depend on numerous factors, especially temperature and pressure. 

Lethal concentration 50 (LC50) is the vapour concentration of a substance in air, which kills 50% of the animals exposed. This estimate comes from a protocol that was statistically controlled. This value depends on the animal chosen for the experiments and exposure time. The three animals that are most commonly used are in descending order rat, mouse and rabbit. It is a parameter that estimates risk level by inhalation, which is the most important means of penetration involving toxic substances in the work place. 

Safety and risk factors evaluate approximately the speed at which a toxic substance reaches a toxic vapour concentration in air. An accurate way to do this would be to know the vapourisation speed for this substance and the air renewal rate of the room in which it is handled. This is why regulations recommend measurement of the vapourisation speed for a particular substance and include it in safety sheets. One can hardly use this figure since it is rarely mentioned. The only substances which were subjected to such measurements are the most commonly used although these figures only are remotely linked to the real conditions. So it was decided to suggest a method derived from the vapour pressure of the substance, which is a factor the vapourisation speed depends on precisely. 

A mixture of acetaldehyde/air of a concentration of 30-60% combusts when it is in contact with substances that are heated at 176°C. The mixture with oxygen of concentration of 60-80% combusts at 105°C. If the object is metallic and furthermore corroded, the ignition can become spontaneous even at ambient temperature. The same goes for corroded aluminium pipes where the AIT reaches 130°C, if vapour concentration is 55-57%. The AIT is also sensitive to the size and shape of the containers that contain acetaldehyde vapour. 

The heat of adsorption of 2-nitropropane is very high, so carbon-containing respirators should not be used in high vapour concentrations. Also, if Hopcalite catalyst (co-precipitated copper(II) oxide and manganese (IV) oxide) is present in the respirator cartridge, ignition may occur. 

The diluted phase coming out from the MC, after having passed through the heat exchangers, reaches the still. The latter consists of a chamber (see Fig. 6.9) where the diluted liquid phase is in equilibrium with a vapour that is practically only 3Fle. In fact, at the typical working temperature of the still ( 0.7K), the 4He vapour concentration is only a few percent (see Section 2.4.1). 

Water vapour makes a sizeable contribution, and probably the largest, to radiation trapping and as the temperature increases the water vapour concentration increases. Temperature rises as a result of increased water vapour concentration and hence a mechanism for a positive feedback in the greenhouse effect that might lead to a runaway greenhouse effect. When the vapour pressure for water reaches saturation, condensation occurs and water rains out of the atmosphere this is what happens on Earth and Mars. On Venus, however, the water vapour pressure never saturates and no precipitation occurs and the global warming continues to increase. Thus Venus suffers from extreme temperatures produced by both its proximity to the Sun and the presence of water vapour and carbon dioxide in its atmosphere. 

The leakage model is deduced from protection factor measurements of people wearing gas masks in the field. The leakage is expressed as a distribution of protection factors as it varies quite a lot over a population of people. The final vapour concentration that a soldier inhales and to which the eyes are exposed, is a fraction-based mean of the breakthrough through the filter and of the leakage at the sides of the mask. 

With the same concept for tray layout as in Figure 11.55, relations for Emi and Emi may be derived. Assuming that the vapour concentration does not change in a horizontal plane, a similar analysis to that above gives ... 

Pupp, C., R. C. Lao, J. J. Murray, and R. F. Pottie. Equilibrium vapour concentrations of some polycyclic aromatic hydrocarbons, As40 and SeOj and the collection efRciencies of these air pollutants. Atmos. Environ. 8 915-925, 1974. 

In theory, induction should be rapid, but in practice the inspired vapour concentration must be increased slowly to avoid airway irritation. MAC is 1.15% in 100% oxygen and 0.56% in 30% oxygen, making it less potent than halothane (0.75% and 0.29% at these oxygen concentrations). Isoflurane is the most potent of all the currently available anaesthetic ethers. Recovery from isoflurane anaesthesia is rapid and clear and the drug is suitable for use in day surgery. Cardiovascular system... 

For instance, aromatic solvent vapours were determined with polyurethane MIPs combined with SAW transducers [124]. That is, first, the hydrophilic quartz surface of SAW was hydrophobized with NW-dimethylaminotrimethylsilane. Then a solution for polymerization was prepared by mixing functional monomers, such as 4,4 -dihydroxydiphenyldimethylmethane, 4,4 -diisocyanatodiphenylmethane and 30% 2,4,4 -triisocyanatodiphenylmethane, with the 1,3,5-trihydroxybenzene crosslinker in the ethyl acetate or ethanol template used also as the solvent for polymerization. Subsequently, the hydrophobized resonator surface was spin-coated with an aliquot of this solution. Finally, the free-radical polymerization has been initiated thermally to form a polyurethane MIP film. The desired vapour concentration and relative humidity of the analyte were achieved by mixing dry air and saturated steam with solvent vapours generated with thermoregulated bubblers. 

Fig. 1. Model of non-polar liquids, left pure liquid cristal-like arrangement of molecules with T-dependent vibration volume and holes. The hole-concentration is equal the vapour concentration. right solution solutes (black) are in the holes and reduce the vapour concentration proportional to the molar concentration of the solute.

Benzene (RL lOp.p.m.). Inhalation of benzene vapour has a chronic cumulative effect leading to acute anaemia and may lead to leukaemia. Very few people can smell benzene in vapour concentrations of less than 75 p.p.m. (i.e. seven times the... 

Fig. 12.7. Interaction of mercury vapour with thin gold films coated by self-assembled monolayer of 1-hexadecanethiol (a) comparison of the kinetics of resistive response for bare (open symbols) and coated (filled symbols) gold films on exposure to 10 ng/1 mercury vapour (b) influence of different mercury vapour concentrations on the resistance of coated electrodes (c) kinetics of changes of the resonance frequency of a 1-hexadecanethiol-coated piezo-quartz due to exposure to 8.3 ng/1 of mercury vapour [25].

Inhalation Route - Estimation of Vapour Exposure. In a study of drift exposure following aerial application of an organo-phosphorus pesticide, Crabbe t al (16) found that the vapour concentration in areas remote from the spray line increased gradually up to 10 hours after the spraying. Increasing temperature was undoubtedly the major explanation for this. Other factors such as volatility of the pesticide, windspeed and sorption properties of the target would also influence the actual vapour concentration on the target. 

The multiplicity of abiotic transformation products which have been detected for aminocarb has prompted a comparison of the anticholinesterase activity, in vivo insect toxicity and relative volatility of a series of oxidation products. Successive oxidations of the aryldimethylamino group resulted in increased toxicity whereas oxidation of the arylmethyl group or of the carbamate N-methyl group considerably reduced toxicity. Saturated vapour concentrations of the toxic transformation products were only slightly lower than the parent carbamate. 

A less widely used approach (8,9) has been to expose a surface of pesticide to an air flow under conditions of a rapid rate of air change such that the concentration of the pesticide in the air surrounding the stagnant boundary layer is far below saturation. Under these conditions the relative rates of diffusion of two pesticides will be inversely related to the square root of their respective molecular weights (Graham s law of Diffusion) and directly related to their saturated vapour concentrations in the boundary layer. 

In the absence of direct field measurements of pesticide fluxes eminating from a sprayed forest a series of suppositions may be drawn from similar observations of losses from treated agricultural crops. The volatilization of dieldrin and heptachlor from a grass pasture was characterized by rather marked diurnal variations in vertical flux intensities of both insecticides during the initial days post application (12). The authors concluded that the volatilization ceased or was greatly reduced with decreased solar radiance. Estimated relative vapour concentrations of dieldrin rapidly declined from saturation 2 hours post application to 10% by evening. This parameter reached a maximum of 30 - 40% on day 2 and 20 - 25% on day 3. Although the saturated vapour concentration of heptachlor is approximately fifty... 

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