Threshold limit values , process

If acetal resins are processed at temperatures substantially above those recommended for the particular grade, minor amounts of formaldehyde may be Hberated. Formaldehyde (qv) is a colorless, lacrimatory gas with a pungent odor and is intensely irritating to mucous membranes. The human nose is sensitive to concentrations in the range of 0.1 to 0.5 ppm. The current threshold limit value for formaldehyde is 1 ppm. 

Recommendations by the ACGIH are classified as threshold limit values (TLV) based on 8-h TWA. Chromium metal and alloys, Cr(II) compounds and Cr(III) compounds, including chromite ore, have a TLV of 0.5 mg/m Cr in air. Water-soluble Cr(VI) compounds have a TLV of 0.05 mg/m Cr. Certain water-insoluble Cr(VI) compounds, ie, the chromates of 2inc, barium, calcium, lead, strontium, sintered chromic acid, and processing chromite ores, also have a TLV of 0.05 mg/m as well as a human carcinogen designation (145). 

This knowledge is also important in order to determine if air tests conducted by OSHA compliance officers are valid. For example, if threshold limit value in the health standard is an 8-hour time-weighted average, the air sample should be obtained by sampling over the entire shift in the employee s breathing zone. It cannot be measured by a few short term samples, even if spaced over the full shift unless the worker is in a relatively fixed location with no variation in his work procedure or in the process. Such an event is generally the exception rather than the rule. 

Toxicity and Hazards. The odor cf ozone can be detected in concn as low as several parts per hundred million by vol (pphm). The threshold limit value (TLV) is O.lppmor 0.2mg/m3 its toxic dose level (TDL), 50% kill concn is 2ppm (Ref 6) Pure 100% liq ozone may be kept safely at 90°K (cooled by liq oxygen) for indefinite periods of time, but the smallest provocation, such as a spark or fast warming, even only up to bp (161°K), causes detonation. The evapn of liq ozone, for example, in the process of the prepn of pure gaseous ozone is, therefore, a dangerous procedure (Ref 3, p 224)... 

Health hazards caused by chemicals are represented by the Toxic Exposure Subindex (ITox). hi the ISI the evaluation of toxic exposure is based on the Threshold Limit Values (TLV) because TLV data is readily available for most substances in process industry. TLV values express the harmful exposure limits of substances in the threshold time of 8 hours. The index value is higher, when the TLV is lower i.e. the substance is more toxic. It is important to use TLVs with same threshold time so that the results are comparable. Score limits in Table 13 are based on Mond Index (ICI, 1985). 

Threshold dose, 25 233. See also TD50 estimating, 25 235 Threshold gain, 14 665 Thresholding process, 18 148 Threshold inhibitors, 26 139 Threshold limit values (TLV), 1 819,... 

An example of a nonoccupational exposure is methanol, which is formed endogenously, probably as the result of the activities of intestinal flora or enzymatic processes. It is present in a number of consumer products. Methanol may be present in low concentrations in some foods, juices, and alcoholic beverages. Methanol can also be derived from the intestinal enzymatic hydrolysis of the artificial sweetener aspartame, which results in methanol absorption from the intestine (Butchko et al. 2002). It is estimated that a 355-mL serving of aspartame-sweetened beverages and of various fruit and tomato juices may contribute about 20-100 mg of dietary methanol (Butchko et al. 2002). For comparison purposes, exposure at the current Threshold Limit Value time-weighted average of methanol (262 mg/m3) would result in a daily dose of about 1,500 mg, assuming an 8-hour inhaled volume of 10 m3 of air and absorption of 57%. 

Kennedy, G.L., Setting a threshold limit value (TLV) the process, Chem. Health Safety, 8,13-15, 2001. 

For chemicals such as food additives, food contaminants, and industrial chemicals the threshold, that is the dose at which toxic effects become apparent, is determined from the dose-response graph and used in the risk assessment process. The threshold value is used, together with safety factors, to determine the acceptable daily intake (ADI) of a food additive, or the tolerable daily intake (TDI) of a food contaminant, or the threshold limit value (TLV in the USA, or maximum exposure limit (MEL) in the UK), for an industrial chemical (see box for calculation). For a drug, information about the dose in animals below which there are no adverse effects will be necessary before human volunteers can be exposed in clinical trials. More extensive safety evaluation is carried out for drugs than for... 

Gas treating is defined here as removal of H2S and CO2. Other sulfur compounds are discussed where applicable. Dehydration and sulfur production are not included, except for when sulfur production in liquid redox processes and selective H2S removal is being discussed. H2S must be removed from natural gas and process streams for health reasons and prevention of corrosion. Natural gas pipeline specifications require no more than 1/4 grain/100 SCF. This is equivalent to 4ppmv or 7 ppmw (for a 0.65 specific gravity gas). By comparison, the human nose can detect 0.13 ppmv and the threshold limit value for prolonged exposure is 10 ppmv. 

Employees are frequently monitored when working in an environment where exposure to toxic metals is a possibility. The most common form of monitoring involves quantification of airborne concentrations of metals in the production process. Threshold limit values for airborne concentrations and time-interval exposure concentrations are defined by the U.S. National Institute for Occupational Safety and Health (NIOSH) to ensure worker safety. Workers may also be monitored by quantification of biological samples. The most common sample used is a random urine sample, and results are expressed in concentration units for the metal of interest per gram of creatinine to normalize for... 

Workplace studies on processing of PUR adhesives have revealed that, with extraction, the TLVs (threshold limit values) for isocyanates were not exceeded in any case, Fig. 5. Extraction can reduce the risks significantly. Extraction combined with absorption or deactivation is preferable. 

ACGIH. 1986. Documentation of the Threshold Limit Values and Biological Exposure Indices, 5th ed. Cincinnati, OH American Conference of Governmental Industrial Hygienists. Adewusi, S. R., and A. A. Akendahunsi. 1994. Cassava processing, consumption, and cyanide toxicity. J. Toxicol. Environ. Health 43 ) 13-23. 

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