Threshold limits solvents

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

The amount of solvent that can be taken into a vessel for dye-penetrant testing or other purposes should be limited so that evaporation of the complete amount will not bring the concentration above the safe concentration, for example, the threshold limit value, making allowance for the air flow if the vessel is force-ventilated. 

The 2003 AGGIE threshold limit value-time-weighted average TLV-TWA for Stoddard solvent is 100 ppm (525mg/m ). 

The numerical value shows the threshold limit value, which is defined as the maximum permissible vapor concentration that the average person can be exposed to for 8 h/day, 5 days/week without harm, in ppm (cm of solvent per 1 m of air). The mark T shows the solvent has Hsted in Title 111 of the Clean Air Act (42 U.S.C. 7401-7626 Public Law 159 from July 14,1955 69 Stat. 322) and the Amendments of 1990 as a hazardous air pollutant. Source Compton, S. and Brownlee, R., Biotechniques, 6,432-440,1988. With permission. 

Table 56-1 Threshold Limit Values (TLVs) of Some Common Air Pollutants and Solvents. ...

Another physiological toxicokinetic model (Tardif et al., 1993b, 1997) has been used to predict potential interactions between, e.g., toluene, ethylbenzene and we/tr-xylene the model and experimental data from exposed volunteers indicate that no biologically significant changes in their toxicokinetics will occur if these three solvents are present in the air as a mixture within the permissible concentrations for mixtures (Tardif et al., 1997). A model approach also predicted that interactions between dichloromethane and toluene at their current threshold limit values are not relevant for humans (Pclekis Krishnan, 1997). 

Solvent flammability, the solvent, and dust loading in the atmosphere of the working environment and of the products in the ease of edible materials are ihe main factors that conslilute health and safety hazards in extraction plants. General safely and environmental standards must therefore he applied and due recognition taken of Ihe most recently published national regulations relating to acceptable threshold limit values (TLVs) for solvents and dusts. 

These agents find wide use as industrial solvents, degreasing agents, and cleaning agents. The substances include carbon tetrachloride, chloroform, trichloroethylene, tetrachloroethylene (perchloroethylene), and 1,1,1-trichloroethane (methyl chloroform). See Table 57-1 for recommended threshold limit values. 

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. 

Worker exposure to alkanes, especially the lower-molecular-mass compounds, is most likely to come from inhalation. In an effort to set reasonable values for the exposure by inhalation of vapors of solvents, hydrocarbons, and other volatile organic liquids, the American Conference of Governmental Industrial Hygienists sets threshold limit values (TLVs) for airborne toxicants.1 2 The time-weighted average exposure (E) is calculated by the formula... 

Styrene monomer concentration in foods packaged in 31 different PS-containing food packages and contact materials averaged 224 mg/kg with two products having concentrations between 800 and 1500 mg/kg, well above the sensory threshold limits (Baner, 2000). Strict specifications for styrene monomers as well as for residual solvents, toluene, and odor and taint transfer for supplier materials should be set (Huber et al., 2002). 

The threshold limits of chemical compounds can lie over a range of 10 orders of magnitude or more (Table 13-3). The saturated hydrocarbons and organic solvents have high threshold limits and are as a consequence relatively odorless. Esters of acrylic acid and a,fl-unsaturated ketones and aldehydes belong to intensive aroma compounds. 

Other corrections that must be considered are the collection efficiency of the charcoal tube and the desorption efficiency of carbon disulfide for this specific solvent. TABLE 1 lists the recommended collection tube for each solvent, flow rate to be used in samplings, and desorption efficiency of many organic compounds. (6) The desorption efficiency of carbon disulfide with the charcoal tubes can be determined by injecting a known amount of solvent onto the charcoal. At least five charcoal tubes are sampled and the 100 mg portion removed and placed in a septum sealed vial. A concentration applicable to the threshold limit value of the organic solvent in question is injected onto the 100 mg of charcoal by piercing the septum cap with a microliter syringe. Several concentrations of solvent should be checked to determine the variation in desorption efficiency with solvent concentration. In like manner, standards are prepared by adding the same amount of solvent to the carbon disulfide solution in the vial. The standards are analyzed with the samples. The percent desorption efficiency (D.E.) is determined as ... 

Hence, organic solvents should be handled with care. In the USA, the threshold limit values [TL values) are used as a measure of the inhalation toxicity for chronic interaction with solvent vapours [90]. In the Federal Republic of Germany, the maximum concentration values at the workplace [MAK values) are used [91, 92]. Threshold limit values refer to airborne concentrations of substances and represent conditions under which it is believed that workers may be repeatedly exposed daily without adverse effect. They refer to time-weighted average concentrations for a normal 8-hour workday... 

The threshold limit value (TLV) is the maximum allowable solvent vapor concentration which should not be exceeded. The values reported in this table are in accordance with the American Conference of Governmental Hygienists (ACGIH). The value is typically given as a time-weighted average (TWA) or a ceiling limit value (CL) which workers can be exposed to for a normal 8-h day, 40-h work week without ill effects. The notation skin indicates that the solvent penetrates the skin and that skin contact should be avoided even if the TLV value is not exceeded. The short-term exposure limit (STEL) is provided, as available, to indicate the vapor concentration value which should not be... 

JP-4, solvents Human (58 aircraft-maintenance workers, 8 unexposed controls) All means below 6 ppm, as measured with industrial-hygiene methods At least 30 wk Exposure well below threshold limit values small but statistically significant increase in frequency of SCE occurred after 30 wk of exposure in sheet-metal workers and painters MN frequency in sheet-metal workers initially showed statistically significant increase but had decreased by 30 wk Lemasters et al. 1997, 1999... 

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