Ambient threshold limit value

Because pulp bleaching agents are, for the most part, reactive oxidising agents, appropriate precautions must be taken in their handling and use. For example, it is important to ensure that the threshold limit values (TLV) (20) in Table 2 are not exceeded in the workplace air. These are airborne concentrations in either parts per million by volume under standard ambient conditions or mg per cubic meter of air. They "represent conditions under which it is beUeved that nearly all workers may be repeatedly exposed, day after day, without adverse effect" (20). TWA refers to a time-weighted average for an 8-h workday STEL is a short-term exposure limit or maximum allowable concentration to which workers can be continuously exposed for 15 minutes. 

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... 

Employing this equation, the concentration of BCME likely to form from any mixture of formaldehyde and HC1 may be calculated. In the workplace, assuming that exposure occurred at the Threshold Limit Values for each (1 ppm for formaldehyde and 5 ppm for HC1), the resulting BCME concentration would be 0.02 ppb. Concentrations in the home and the ambient environment are likely to be significantly lower for one or both reactants, and concentrations of BCME would be expected to be essentially negligible. 

Ozone (O3) is a bluish irritant gas that occurs normally in the earth s atmosphere, where it is an important absorbent of ultraviolet light. In the workplace, it can occur around high-voltage electrical equipment and around ozone-producing devices used for air and water purification. It is also an important oxidant found in polluted urban air. The effect of low ambient levels of ozone on admission to Ontario, Canada, hospitals for respiratory problems revealed a near-linear gradient between exposure (1-hour level, 20-100 ppb) and response. See Table 57-1 for 1999-2000 threshold limit values. 

Ambient mercury vapor concentrations of 100 pg/ m or higher have been measured during chloralkah production and mercury mining [18]. Adverse health effects were common sequelae from such exposures. During recent years, most countries have reduced mercury s occupational threshold limit value to 50... 

The USEPA standards for 24-h PM, and PM2.5 concentrations in ambient environments are 150 and 65 pg/m , respectively. Indeed in some settings the levels exceed what is considered acceptable for even occupational exposures. The threshold limit value adopted by the American Conference of Governmental Industrial Hygienists for respirable dusts is 5,000 pg/m and for carbon monoxide is 29 mg/m The comparison with these health-based standards (although currently available for settings other than indoor household environments) indicates the potential for significant health risks. 

There is no known biochemical reaction in organisms that applies Hg as an essential element. Mercury is the only metal which is a liquid at ordinary temperatures. The boiling point of this metal is 357 °C. This temperature is relatively low for metals and its vapor pressure is significant even at room temperature. The threshold limit value (TLV) of elemental mercury is 0.05 mg/m- a value that is less than the equilibrium vapor pressure at ambient temperatures. However, in the mercury miners in Sicily, where the mercury occurs in shales, the miners are exposed to elemental mercury vapor, which content in the air may reach toxic levels of about 5 mg/nr Another source of exposure in mines is the mercury-containing dust. 

U.S. National Institute for Occupational Safety and Health (NIOSH) is 35 ppm with a ceiling value of 200 ppm. The U.S. Environmental Protection Agency (EPA) has set an ambient air quality standard of 9 ppm, averaged over an 8-h period, and 35 ppm for 1 h, not to be exceeded more than once a year. The American Conference of Governmental and Industrial Hygienists (ACGIH) has set a threshold limit value for CO of 25 ppm. ... 

The advantages of carbon dioxide as solvent have been well publicized it is, in fact, classified as GRAS - generally regarded as safe, it has low toxicity (threshold limit value - TLV = 5000 ppm), it is supercritical just above ambient temperature (critical temperature 31 C) and it is cheap. Also, like other supercritical fluids, it has advantageous gas-like transport properties, such as low viscosity and high diffusivity. 

Metallic or elemental mercury volatilizes to mercury vapor at ambient air temperatures, and most human exposure is by way of inhalation. The saturated vapor pressure at 20.0°C is 13.2mg/m. This value far exceeds the threshold limited value (TLV) of 0.05 mg/m accordingly, mercury intoxication due to inhalation of the vapor readily occurs in various occupational and environmental situations. Mercury vapor readily diffuses across the alveolar membrane and is hpid soluble so that it has an affinity for the central nervous system and red blood cells. Metallic mercury, unlike mercury vapor, is only slowly absorbed by the G1 tract (0.01%) at a rate related to the vaporization of the elemental mercury and is of negligible toxicological significance. 

There are no established tolerances for chlordane or heptachlor in the ambient air in home environments. An interim guideline level of 5.0 pg/m3 (chlordane) and 2.0 pg/m (heptachlor) has been recommended by the Committee on toxicology of the National Academy of Sciences (8). The maximum allowable limit in work-space air during a 40 h workweek (Threshold Limit Value, Time Weighted Average) (TLV-TWA) is 500 pg/m for chlordane and heptachlor (9). 

Kramer et al. found xylenes during paint production and paint-spraying in ambient air and in the blood and urine of workers. Threshold limit values (TLV) and biological exposure indices (BEI) were not exceeded. ... 

The exposure to solvents is regulated by relevant threshold limit values. Exposure and exposure values ean be eontrolled by defined methods (e.g., ambient and biologieal monitoring). 

According to the OSHA Technical Manual, which prescribes workloads for workers under temperatures typically experienced outdoors during the summer months, to keep from exceeding the Threshold Limit Value (TLV) when the ambient temperature is above 86° F, the work regimen will consist of 25 percent work and 75 percent rest. This type of schedule plays havoc on productivity, as does the lost time incurred when a worker succumbs to heat stress. Plus, as workers become fatigued by back-to-back days — where each day they approach their TLV — their quality of life diminishes. That affects productivity and causes a rise in sick days. 

Through EU legislation, major air pollutants have been regulated. For example, through an EU Directive (EC 1999), the EU has estabhshed limit values for concentrations of sulfur dioxide, nitrogen dioxide and nitrogen oxides, particulate matter and lead, as well as alert thresholds for concentrations of sulfur dioxide and nitrogen oxide, in ambient air. Member States must take the measures necessary to ensure that concentrations of the pollutants in ambient air do not exceed the limit values. 

During the past 15 years formaldehyde exposures and emission limits have been significantly lowered. Occuptional threshold limits are now 1.0 ppm or lower in most countries, and actual industrial exposures are almost always half of this value or less. Indoor air standards of 0.1 ppm are now contemplated in several nations, following established procedures for correlating occupational levels of toxic chemicals with ambient air levels. Furthermore, emission standards for UF-bonded wood products have been developed that allow the prediction of formaldehyde levels under various product use conditions before formaldehyde emitting products are installed. 

Many of these food and pharmaceutical products are heat sensitive that is, the finished product may be damaged or destroyed if it is exposed to too great a temperature over an extended period of time. Even common products like tomato catsup and penicillin spoil or lose their efficacy when exposed to ambient temperatures for long periods of time. The chemical reactions that limit shelf life are strongly temperature dependent. Some biological products may be handled at elevated temperatures in dilute solutions, but may degrade at the same temperature once the concentration exceeds a certain threshold value. 

---