Limiting value of exposure

Because naphthalene vapors can cause eye irritation at concentrations of 15 ppm in air and because continued exposure may result in adverse effects to the eye, a threshold limit value of 10 ppm (50 mg/m ) has been set by the ACGIH (45). This amount is about 30% of the air-saturation value at 27°C. 

In accordance with demonstrated differences between the various asbestos fiber types, the workplace regulation in many countries specifies different exposure limits for chrysotile and the amphiboles (45). Moreover, to alleviate estabHshed, or apprehended, risk from substitute fibers, the regulation often specifies maximum exposure limits for synthetic fibers (46) values of exposure limits adopted in leading industrial countries are coUected in Table 8. 

Inhalation. The threshold limit value of HCN is 4.7 ppm. This is defined as the maximum average safe exposure limit for a 15-min period by the Occupational Safety and Health Administration. Exposure to 20 ppm of HCN in air causes slight warning symptoms after several hours 50 ppm causes disturbances within an hour 100 ppm is dangerous for exposures of 30 to 60 min and 300 ppm can be rapidly fatal unless prompt, effective first aid is adininistered. There is always a small concentration of cyanide (0.02 to 0.04 mg/L) in the blood, and the body has a mechanism for continuous removal of small amounts, such as from smoking, by converting it to thiocyanate, which is discharged in the urine. 

INRS finds it very useful when giving advice to epidemiologists who look for an approximate value for a substance, which has not yet been analysed (called calculated limiting vaiue of exposure). 

To protect humans and other mammals, proposed air-quality criteria range from 0.01 to less than 1.0 mg/m3 for metallic nickel and slightly soluble nickel compounds, 0.015-0.5 mg/m3 for water soluble nickel compounds, and 0.005 to 0.7 mg/m3 for nickel carbonyl (Table 6.10). Inhalation of nickel subsulfide concentrations (0.11 to 1.8 mg Ni/m3) near the current threshold limit value of 1 mg Ni/m3 can produce detrimental changes in the respiratory tract of rats after only a few days of exposure (Benson et al. 1995). Additional animal studies are recommended to identify minimally effective inhalation exposure levels for the various nickel compounds (USPHS 1993). Continued monitoring of nickel refining, nickel-cadmium battery manufacture, and nickel powder metallurgy installations is recommended because ambient air levels of bioavailable nickel at these... 

If spilled on the skin or in the eyes liquid N2IL, can cause severe local damage or burns and can cause dermatitis. In addition it can penetrate skin to cause systemic effects similar to those produced when the compound is swallowed or inhaled. Inhalation of the vapor causes local irritation of the respiratory tract and eyes. On short exposure systemic effects involve the central nervous system. Resultant symptoms include tremors, on exposure to higher concentrations, convulsions and possibly death follow. Repeated exposures may cause toxic damage to the liver (fatty liver) and kidney (interstitial nephritis), as well as anemia. The threshold limit value of hydrazine is 1 ppm (1.3 mg/m3)(Ref 20) (See also Refs 27 c and 33a)... 

The MAK values are mean concentrations over the complete time of exposure. Allowable concentration peaks are restricted to limited values of concentration highs, period of exposure and frequency of these events per shift. In rating the hazardous potential of chemical exposure, animal experiments arc used and in addition compared with those of known human exposure, thus a high safety standard is guarantied. 

The American Conference of Governmental Industrial Hygienists (ACGIH) (1997) has not proposed any occupational exposure limit for 1,2-dimethylhydrazine in workplace air. Sweden and Switzerland have 8-h time-weighted average threshold limit values of 0.2 mg/ni and 1.2 mg/m respectively, for exposure in workplace air, with a skin notation (International Labour Office, 1991). 

A word here on the toxicity of V compds The compds act chiefly as irritants to the con-junctivae and respiratory tract, turning the tongue green. Exptl biochemical studies show that V compds inhibit cholesterol synthesis and the activity of the enzyme cholinesterase. Prolonged exposure to V compds may lead to fatal pulminary involvement. The Threshold Limiting Values of these compds, in particular the highly toxic pentoxide, are dust, 0.5mg/CM fumes, 0.05mg/CM (Refs 7,16 18)... 

Such conditions with high carbon black levels would not occur under today s environment of carbon black production plants. Most of the carbon black producing countries have adopted the TLV (Threshold Limit Value) of USA of 3.5 mg/m3 [4.48]. Extensive sampling in a number of carbon black plants in Europe [4.49] provided the results that the occupational exposure standard (OES) for carbon black is 3.5 mg/m3 for an 8-hr TWA (time weighted average) and 7 mg/m3 for the shortterm exposure limit (STEL). 

The threshold limiting value of respiratory exposure is 1 mg/cm of air. In the (breathable) atmosphere,. .. 0.125 to 0.50ppm may be mildly annoying and 1.5 to 2.5ppm can be definitely unpleasant 10 to 20ppm is unbearable. . . Body contact results in rapid de-... 

This methodology was a first approach to estimate population exposure, calculated as the total daily values above the thresholds recommended by the European Commission Directive for long- and short-term health effects. Obtained results revealed that in Lisbon city centre a large number of persons are exposed to PM levels exceeding the legislated daily limit value of 50 pg m 3. 

Inhalation Exposure Levels. For setting acceptable maximum inhalation exposure levels, we usually use the lowest threshold limit values of those set by Federal OSHA (Occupational Safety and Health Administration), California OSHA, or the ACGIH (American Conference of Governmental Industrial Hygienists). Sometimes, as with ethylene dibromide, we accept a NIOSH (National Institute of Occupational Safety and Health) recommended standard which is lower than the three standard-setting entities previously mentioned. In other cases, when a standard has not been set by any of these groups, we set one ourselves based on available inhalation toxicity information. 

The threshold limit values for exposure to various types of radiation given must not be exceeded. For electromagnetic fields at 60 Hz, the threshold limit is 10 Gauss and the limit is 1 Gauss for people with pacemakers. 

The permissible exposure limit (time-weighted average, TWA) for octane is 500 ppm (2335 mgm ) while the American Conference of Governmental Industrial Hygienists recommends a TWA threshold limit value of 300 ppm (1400 mg m ). National... 

Recommendations regarding limits for occupational exposure to propylene oxide differ markedly. The current 8 h time-weighted average (TWA) established by the Occupational Safety and Health Administration in the United States is 100 ppm. The American Conference of Governmental Industrial Hygienists recommends a threshold limit value of 2 ppm as an 8 h TWA. In European countries, the limits of exposure are in the range 1-20ppm (8h TWA). 

The small magnitude of effect sizes from observations of chronic users of cannabis suggests that cannabis compounds, if found to have therapeutic value, should have a good margin of safety from a neurocognitive standpoint under the more limited conditions of exposure that would likely obtain in a medical setting. 

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