Benzene limit values

COM(98j591 Proposal for a Directive on limit values for benzene and carbon monoxide m ambient air... 

It will be observed in Fig. 38 that the slope of the x/c plot for polyisobutylene in benzene at 30°C is small and that there is no evidence of curvature. This is in accord with Eq. (13), which requires the magnitude of the curvature to vary as the square of the slope. Of more immediate importance is the fact that the same limiting values, ( /c)o, are obtained in different solvents, despite widely differing behavior at higher concentrations. Hence the observed molecular weights are independent of the solvent employed within experimental error. In... 

A comparison of the thus calculated with the measured specific rotations of the 0th- to 4th-generation dendrimers of this kind gave a close resemblance, with a curve, approaching asymptotically a limiting value (Fig. 26). It was also shown that the shape of this curve was independent of solvent, concentration and temperature. This was not the case when CD spectra of these dendrimers were compared (Fig. 27) in solvents such as CH2C12 and f-butyl methyl ether a constant rise of the Cotton effect was observed, which correlates with the increasing amount of benzene chromophores in the dendrimers. However, in the... 

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for benzene is 0.5 ppm (1.6mg/m ) with a TLV STEL of 2.5ppm (8mg/m ) and an Al-confirmed human carcinogen designation and a notation for skin absorption. 

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for divinyl benzene is 10 ppm (53mg/m ). 

Butadiene is a colorless, odorless, flammable gas, with a bp of -4.7°C. As of 2000 butadiene has been on the Known to Be a Human Carcinogen list of the Department of Health and Human Services. It has a time-weighted average threshold limit value (TLV) of 2 ppm. TLVs and carcinogens will be discussed more fully under benzene. Butadiene is expensive to store because it polymerizes easily and must be refrigerated. 

Benzene has a low threshold limit value or TLV. The time weighted average TLV (TWA) is the allowable exposure for an average 8 hr day or a 40 hr week. The short-term exposure limit TLV (STEL) is the maximum allowable exposure for any 15-min period. For benzene the TWA = 0.5 ppm and the STEL is 2.5 ppm, as given by the American Conference of Governmental Industrial Hygienists (ACGIH). This allowable exposure is much lower than those for toluene and xylene, probably because these latter two compounds have benzyl ic positions that are easily oxidized in vivo to compounds that can be eliminated from the body. 

An example of an evaluation undertaken according to this protocol is for the measurement of benzene in ambient air by tube type samplers subject to thermal desorption (EN, 2005b) and samplers subject to solvent desorption (EN, 2005a). These standards were developed specifically to provide measurement methods meeting requirements for checking compliance with the air quality standard for benzene set by the European Ambient Air Quality Directive (Directive 96/62/EC, 1996). Evaluation of published data concerning the samplers under the test conditions enabled an evaluation of the expanded relative uncertainty of measurement at a limit value (5 pgnT3) for benzene in air and for solvent and thermally desorbed samplers a value of 13.4% was obtained. 

Benzene is widely used for its solvent properties and as an intermediate in the synthesis of other chemicals. The 1999-2000 recommended threshold limit values are given in Table 57-1. The acute toxic effect of benzene is depression of the central nervous system. Exposure to 7500 ppm for 30 minutes can be fatal. Exposure to concentrations larger than 3000 ppm may cause euphoria, nausea, locomotor problems, and coma vertigo, drowsiness, headache, and nausea may occur at concentrations ranging from 250 to 500 ppm. No specific treatment exists for the acute toxic effect of benzene. 

Toluene (methylbenzene) does not possess the myelotoxic properties of benzene, nor has it been associated with leukemia. It is, however, a central nervous system depressant. See Table 57-1 for the threshold limit values. Exposure to 800 ppm can lead to severe fatigue and ataxia 10,000 ppm can produce rapid loss of consciousness. Chronic effects of long-term toluene exposure are unclear because human studies indicating behavioral effects usually concern exposures to several solvents, not toluene alone. In limited occupational studies, however, metabolic interactions and modification of toluene s effects have not been observed in workers also exposed to other solvents. 

Several choices are available in defining the standard state of the solute. If the solute is a liquid which is miscible with the solvent (as, for example, in a benzene-toluene mixture), then the standard state is again the pure liquid. Several different standard states have been used for solutions of solutes of limited solubility. In developing a relationship between drug activity and thermodynamic activity, the pure substance has been used as the standard state. The activity of the dmg in solution was then taken to be the ratio of its concentration to its saturation solubility. The use of a pure substance as the standard state is of course of limited value since a different state is used for each compound. A more feasible approach is to use the infinitely dilute solution of the compound as the reference state. Since the activity equals the concentration in such solutions, however, it is not equal to unity as it should be for a standard state. This difficulty is overcome by defining the standard state as a hypothetical solution of unit concentration possessing, at the same time, the properties of an infinitely dilute solution. Some workers have chosen to... 

Reliable fluorescence quantum yields and lifetimes in the solid phase are difficult to determine, and accurate data are sparse (see Tables 10 and 11). It is well established that fluorescence and lifetimes of dilute solutions of benzene Increase with decreasing temperature (8,119). In a recent study of similar molecules (156-158), it was shown that the Increase in both 0p and Tp is smooth, and that both these quantities tend towards a limiting value at low temperature. An analysis of the temperature dependence of the two parameters for benzene in a variety of solvents (119) has indicated that the limiting values for both should be reached at a temperature well above 77°K, since the controlling variable is the radiationless Channel III process(es)... 

The odor threshold for benzene is 30 ppm, but the current American Conference of Governmental Industrial Hygienists Threshold Limit Value considered safe for occupational exposure (8 h day) is below that threshold at 0.5 ppm. The Occupational Safety and Health Administration permissible exposure limit (PEL) is 1 ppm, with a short-term exposure limit (STEL) of 5 ppm. The National Institute for Occupational Safety and Health recommends an exposure limit (recommended exposure limit) of 0.1 ppm with a STEL of 1 ppm. 

The kf versus [lipid] dependencies for Fe(CN)s are different. Although the ET rate decreases markedly with increasing concentration of lipid, it does not approach zero at higher concentrations, but reaches the limiting value at about 50 /xM. This saturation suggests the formation of a complete phospholipid monolayer at the ITIES. The formation of compact phospholipid monolayers at similar lipid concentrations was observed at water/nitro-benzene (40a) and water/dichloroethane (40b) interfaces. 

Threshold limit values as measured by short-term exposure. A typical worker can be exposed to this time-weighted average concentration of the substance for 15 min without ill effects. (UK based on 10-min TWA), benzene, 50 ppm. 

In accordance with the framework directive limit values have to be established in daughter directives. Two of these daughter directives have already been adopted, the first one relating to limit values for sulfur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 99/30/EC 1999 see Table 1.8), and the second one on limit values for benzene and carbon monoxide (Council Directive 00/69/EC 2000), which have to be transferred into national legislation by July 19, 2001 and December 13,... 

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