Time-weighted average exposures

Phosphine has an 8-h time-weighted average exposure limit of 0.3 ppm (13). Under alkaline conditions the rate of PH formation is high. At neutral or acidic pH, the PH generation is slow but stiU very ha2ardous if the PH is allowed to accumulate in a confined vapor space. The safest commercial handling conditions for molten phosphoms are generally considered to be from pH 6 to 8 at 45—65°C. 

Carboxyhc acid dust and vapors are generally described as being destmctive to tissues of the mucous membrane, eyes, and skin. The small molecules such as formic, acetic, propionic, butyric, and acryUc acids tend to be the most aggressive (Table 11) (83). Formic, acetic, propionic, acryUc, and methacrylic acids have time weighted-average exposure limits of 20 ppm or lower. AcryUc acid showed an LD q of 33.5 mg/kg from oral adrninistration to rats. 

As an example, several air samples collected during an 8-hour work shift for benzene (8-hour time-weighted average = 10 ppm) were 3 hours at 4 ppm, 1 hour at 15 ppm, 2 hours at 6 ppm and 2 hours at 9 ppm. The employee s time-weighted average exposure would be ... 

Another type of time-weighted average exposure limit is the decision level (DL), which is expressed as a fraction of the OEL. In general, it is based on judgment, and it is greater than a dose of 50% and usually corresponds to one-fourth of the dose. For special substances, such as carcinogens, it should... 

WPL AEL Worker Population Airborne Exposure Limits developed for the military by the CDC. They are based on a time-weighted average exposure over an 8-h period and 40-h work week. 

STEL Short-Term Exposure Limits based on a time-weighted average exposure of 15 min (unless otherwise noted). A [Skin] notation indicates that percutaneous absorption of the material is a potential hazard and may contribute to the overall exposure. 

The PELs are promulgated by OSHA and have force of law. These levels are similar to the ACGIH criteria for TLV-TWAs because they are also based on 8-hr time-weighted average exposures. OSHA-cited acceptable ceiling concentrations, excursion limits, or action levels may be appropriate for use as benchmarks. 

The estimated ambient vapor-phase concentrations of chemicals in indoor air were, in general, below the NIOSH time-weighted average exposure limits for a 40 hr workweek. However, the authors of this study concluded that the consequences of long term human exposure to these complex mixtures of airborne... 

A STEL is defined as a 15-min time-weighted average exposure which should not be exceeded at any time during a workday even if the 8-h TWA is within the TLV. Exposures at the STEL should not be longer than 15 min and should not be repeated more thanfour times per day. There should be at least 60 minutes between successive exposures at the STEL. An averaging period other than 15 min may be recommended when warranted by observed biological effects. 

Evans, M., et al, The Practical Application of the Praton Diffusion Sampler for the Measurement of Time-Weighted Average Exposure to Volatile Organic Substances in Air,... 

Table 6. Eight-hour time-weighted average exposure levels in personal breathing zone samples at four butadiene monomer production facilities, United States, 1985...

Occupational exposure to 1,3-butadiene occurs in the production of monomeric 1,3-butadiene and of 1,3-butadiene-based polymers and 1,3-butadiene-derived products. The mean full-shift, time-weighted average exposure levels measured for workers in these industries have usually been below 10 ppm [22 mg/m- ], although that level may be exceeded during some short-term activities. Recent data from monomer extraction and styrene-butadiene rubber plants showed lower average concentrations (< 5 ppm [< 11 mg/m ]). 1,3-Butadiene is not usually found at detectable levels in workplace air during manufacture of finished rubber and plastic products. 

The American Conference of Governmental Industrial Hygienists (ACGIH) (1997) has not proposed any occupational exposure limit for 1,2-epoxybutane in workplace air. However, manufacturers in the United States have recommended a voluntary standard of 40 ppm [118 mg/m ] for an 8-h time-weighted average exposure limit (United States National Toxicology Program, 1988). 

A longitudinal study was conducted in 10 forestry employees and six unexposed men in Colorado, United States, with an exposure time of approximately six weeks. Spenn velocity decreased in all 10 exposed men and in only two unexposed men. Semen volume was also decreased. The time-weighted average exposure of these men was 60 ppb [0.46 mg/m ] with peak exposures in the order of 2165 ppb [16.6 mg/m ]. The authors suggested that the exposure may have effected the accessory sex glands and that ethylene dibromide may have multiple sites of action (Schrader et al., 1988). 

In a study of 64 men employed in the production of chlorinated compounds [time-weighted average exposures, < 1 ppm [4.5 mg/m l 1,3-dichloropropene, 3.1 mg/m allyl chloride and 3.8 mg/m epichlorohydrin], sperm counts and percentages of normal sperm were similar in the study group and among 63 controls. The volunteer participation rate for the study group was 64% (lARC, 1986). 

The concentrations of white phosphorus levels in the atmosphere of a wet fill production line at Pine Bluff Arsenal, Arkansas, were measured in 1975 (Berkowitz et al. 1981). The levels of white phosphorus at this location exceeded the OSHA 8-hour time-weighted average exposure limit of 0.1 mg/m3. At one location, the concentration of elemental phosphorus was 0.45 mg/m3 and may have been underestimated due to poor quality control (Berkowitz et al. 

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... 

A significant correlation (r=0.71) was found between exposure levels and postshift, urinary chromium in workers exposed to chromium(VI) as chromium trioxide in the chrome plating industry. The urinary chromium level of 5.2 pg/L reflects a time-weighted average exposure of 0.002 mg chromium(VI)/m3. This correlation was obtained by excluding workers with obvious skin contamination (Lindberg and... 

Canada has generated time-weighted average exposures for occupational and residential post-application exposnre scenarios where dislodgeable (transferable) foliar residue data have yielded dissipation curves which allow generation of daily exposure estimates on snccessive days following apphcation. These estimates have potential utility in risk assessments not based on acute toxicological endpoints. 

Workplace exposure limits (WELs) were adopted in the UK in 2005 to replace maximum exposure limits (MELs) and occupational exposnre standards (OESs). Workplace exposure limits—longterm exposnre limits (eight-hour time-weighted average exposures) and short-term exposme limits (hfteen-minnte time-weighted average exposmes)—are set by the Health and Safety Executive (HSE) and pnblished in document EH40 (http //www.hse.gov.uk/coshh/tablel.pdf). 

Within the refinery fence Une, maximum observed and/or calculated airborne concentrations of chemicals reported in the airnual TRI were below OSHA action and permissible exposure levels for 8-hour time-weighted average exposures. Impacts on air quality by the refinery were calculated using air dispersion modeling techniques and the emissions inventory developed during this study. 

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