Sulfur dioxide exposure limits

PPS dust should be treated as a nuisance particulate. The OSHA permissible exposure limit for respirable dust is 5 mg/m for dust containing no asbestos and less than 1% siUca. The principal decomposition products released during mol ding of PPS and their permissible exposure limits are given in Table 10. Sulfur dioxide and carbonyl sulfide are the most significant off-gases for production of mucous membrane irritation. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

Health, Safety, and Environmental Factors. Sulfur dioxide has only a moderate acute toxicity (183). The lowest pubHshed human lethal concentration is 1000 ppm for 10 months. The lowest pubHshed human toxic concentration by inhalation is 3 ppm for 5 days or 12 ppm for 1 hour. The lowest pubHshed human lethal concentration is 3000 ppm for 5 months. In solution (as sulfurous acid), the lowest pubHshed toxic dose is 500 flg/kg causing gastrointestinal disturbances. Considerable data is available by other modes of exposure and to other species NIOSH standards are a time-weighted average of 2 ppm and a short-term exposure limit of 5 ppm (183). 

Process Applications TABLE 8.6.2 Exposure Limits for Sulfur Dioxide 277... 

Community exposure studies typically included concomitant exposures to particles, so the studies have limited utility in defining causation sulfur dioxide was but one of several agents contributing to observed effects. The epidemiologic studies suggest that the respiratory effects of exposure to sulfur dioxide in combination with particles, are greater than are the effects caused by sulfur dioxide alone in healthy individuals-especially in the elderly and those with preexisting cardiac or respiratory disease (WHO 1979). 

WHO (World Health Organization). 1984. Sulfur dioxide. Pp. 115-150 in Recommended Health-Based Occupational Exposure Limits for Respiratory Irritants. WHO Technical Report Series 707. Geneva World Health Organization. 

Exposure limits The U.S. EPA has set a limit of 0.03 ppm for sulfur dioxide for long-term exposure. OSHA has set a limit of 2 ppm over an 8-hour workday (TWA). ... 

The NAC/AEGL Committee estimates the range in variability of response to specific chemical exposures primarily on the basis of quantitative human data. Acceptable experimental data are more likely to be available for AEGL-1 and AEGL-2 endpoints than for AEGL-3 endpoints. For example, numerous studies have considered induction of bronchospasm after controlled exposmes to sulfur dioxide (SO2) in asthmatic and nonasthmatic individuals (see references below). There is marked individual variability in the severity of reaction to inhalation of low concentrations of SO2. Asthmatics, individuals with hyper-reactive airways, smokers, and those with chronic respiratory or cardiac disease respond at relatively lower concentrations (Aleksieva 1983 Simon 1986). Susceptibility may also be increased in people over 60 years of age, but reports have not been consistent (Rondinelli et al. 1987 Koenig et al. 1993). By contrast, comparable human data for AEGL-3 tier concentrations are limited to anecdotal case reports. 

The Clean Air Act recognizes a number of so-called primary air pollutants, and the EPA has established standards for these substances. Ozone, nitrogen dioxide, and sulfur dioxide are among these (the others are carbon monoxide and lead, discussed below, and total suspended particulates ). EPA s standard for ozone is 0.12 parts of the gas per million parts of air (0.12 ppm), as a one-hour exposure limit that is not to be exceeded more than once yearly. Nitrogen dioxide s limit is 0.05 ppm as an annual average. These standards are designed to prevent chronic respiratory toxicity of any type. 

I. Mechanism of toxicity. Sulfur dioxide is an irritant because it rapidly forms sulfurous acid on contact with moist mucous membranes. Most effects occur in the upper respiratory tract because 90% of Inhaled sulfur dioxide is rapidly deposited there, but with very large exposures sufficient gas reaches the lower airways to cause chemical pneumonitis and pulmonary edema, ii. Toxic dose. The sharp odor or taste of sulfur dioxide is noticed at 1-5 ppm. Throat and conjunctival irritation begins at 8-12 ppm and is severe at 50 ppm. The ACGIH-recommended workplace permissible limit (TLV-TWA) is 2 ppm (5.2 mg/m ) as an 8-hour time-weighted average, the short-term exposure limit (STEL) is 5 ppm (13 mg/m ), and the air level considered immediately dangerous to life or health (IDLH) is 100 ppm. Persons with asthma may experience bron-chospasm with brief exposure to 0.5-1 ppm. 

Endosulfan (CAS 115-29-7) Inhalation and skin absorption are major routes of exposure. Symptoms Include nausea, confusion, excitement, twitching, and convulsions. Animal studies suggest liver and kidney Injury from very high exposures. Limited evidence for adverse effects on male reproduction and fetal development In animal studies. See also p 161. 0.1 mg/m S Chlorinated hydrocarbon insecticide. Tan, waxy solid with a mild sulfur dioxide odor. Thermal-breakdown products include oxides of sulfur and hydrogen chloride. 

OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 5 ppm (13 mg/m ) for sulfur dioxide. TWA-PEL is the exposure limit that shall not be exceeded by the 8-hour TWA in any 8-hour work shift of a 40-hour workweek [3]. See Table 2. 

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