Vapor concentrator

Full eye protection should be worn whenever handling acryhc monomers contact lenses must never be worn. Prolonged exposure to Hquid or vapor can result in permanent eye damage or blindness. Excessive exposure to vapors causes nose and throat irritation, headaches, nausea, vomiting, and dizziness or drowsiness (solvent narcosis). Overexposure may cause central nervous system depression. Both proper respiratory protection and good ventilation are necessary wherever the possibiHty of high vapor concentration arises. 

Fig. 3. Passage of the adsorption wave through a stationary bed during the course of an adsorption cycle. The progressing S-shaped curves indicate the nonadsorbed vapor concentration by position in the bed at different time periods. represents the maximum permissible oudet concentration for release...

Exposure to formic acid vapor causes irritation of the eyes and respiratory tract. The TLV/TWA occupational exposure limit is 5 ppm (40). Self-contained breathing apparatus should be used when there is a risk of exposure to high vapor concentrations. 

Organic fluids also are mixed with water to serve as secondary coolants. The most commonly used fluid is ethylene glycol. Others include propjiene glycol, methanol (qv), ethanol, glycerol (qv), and 2-propanol (see Propyl alcohols, isopropyl alcohol). These solutions must also be inhibited against corrosion. Some of these, particularly methanol, may form flammable vapor concentrations at high temperatures. 

Aromatic Hydrocarbons. These are the most toxic of the hydrocarbons and inhalation of the vapor can cause acute intoxication. Benzene is particularly toxic and long-term exposure can cause anemia and leukopenia, even with concentrations too low for detection by odor or simple instmments. The currendy acceptable average vapor concentration for benzene is no more than 1 ppm. PolycycHc aromatics are not sufftcientiy volatile to present a threat by inhalation (except from pyrolysis of tobacco), but it is known that certain industrial products, such as coal tar, are rich in polycycHc aromatics and continued exposure of human skin to these products results in cancer. 

Ammonia is a strong local irritant which also has a corrosive effect on the eyes and the membranes of the pulmonary system. Vapor concentrations of 10,000 ppm are mildly irritating to the skin, whereas 30,000 ppm may cause bums. The physiological effects from inhalation are described in Table 16. Prolonged, intentional exposure to high levels of ammonia is unlikely because its characteristic odor can be detected at levels as low as 1 —5 ppm (94). The real danger occurs when escape is impossible, or the exposure victim has lost consciousness. 

Use of isopropyl alcohol in industrial appHcations does not present a health hazard. The alcohol produces anesthetic effects in high vapor concentration. Consequently, the OSHA permissible exposure limit (PEL) and the ACGIH threshold limit value (TLV) have been estabUshed at 400 ppm (0.098 mg/L) for an 8-h exposure (TWA) (138). This level causes a mild irritation of the eyes, nose, and throat (139). However, the TLV level does not produce symptoms of anesthesia (140). The OSHA and ACGIH short-term exposure limits (STELs) are 500 ppm. The odor threshold for isopropyl alcohol ranges from 3 to 200 ppm, which is the minimum concentration having identifiable odor (141). 

Eye contact can cause irritation or bums. Repeated skin contact can result iu dermatitis. Exposure to excessive vapor concentrations irritates the eyes and respiratory tract. Very high concentrations have a narcotic effect (43). 

Under most circumstances the equiUbtium shape of silicon crystals is octahedral, ie, the slowest-growing faces are (111). However, external conditions can radically alter that shape. For example, when growth is from the vapor, concentration gradients in the gas stream may affect the shape, and when growth is from the melt, the shape is primarily determined by thermal gradients in the melt. 

Health and Safety. Halosilane vapors react with moist air to produce the respective hydrohalogen acid mist. Federal standards have not set exposure to halosilanes, but it is generally beheved that there is no serious risk if vapor concentrations are maintained below a level that produces an irritating concentration of acid mist. The exposure threshold limit value (TLV) for HCl is 5 ppm, expressed as a ceiling limit. Because most people experience odor and irritation at or below 5 ppm, HCl is considered to have good warning properties. 

Figure 3 gives the % humidity as the measure of vapor concentration, whereas Figure 2 gives relative humidity in %. 

Toxicity Data on Af- Vinyl-2-Pyrrolidinone. Results of a chronic inhalation study in rats warrant a review of industrial hygiene practices to assure that VP vapor concentrations are maintained at a safe level. One of the manufacturers, ISP, recommends that an appropriate workplace exposure limit be set at 0.1 ppm (vapor) (9). Additionally, normal hygienic practices and precautions are recommended, such as prompt removal from skin and avoidance of ingestion. In case of accidental eye contact, immediately flush with water for at least 15 minutes and seek medical attention. Refer to the manufacturers Material Safety Data Sheets for more detailed information. Table 3 provides some toxicity data. 

Human sensitization studies were negative at 10% solution (47). Undiluted benzyl alcohol produces moderate dermal irritation in guinea pigs and mild dermal irritation in rabbits (48,49). Severe eye irritation was noted in a rabbit study (50). Acute oral rat LD q values were reported between 1.23 and 3.10 g/kg (50—52). A dermal rabbit LD q value of 2.0 g/kg has been reported (49). Rats died after 2 h when exposed to a 200-ppm vapor concentration (53). Benzyl alcohol is readily oxidized in animals and humans to benzoic acid [65-85-0] which is then conjugated with glycine [56-40-6], and rapidly eliminated in the urine as hippuric acid [495-69-2] (54). 

The characteristics of WC, especially grain size, are determined by purity, particle shape and grain size of the starting material, and the conditions employed for reduction and carburization. The course of the reaction WO3 — W — WC is dependent on temperature, gas flow rates, water-vapor concentration in the gas, and the depth of the powder bed. All these factors affect the coarsening of the grain. 

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27). 

Eatahties have occurred when unprotected workers have entered an unventilated tank or piece of equipment that contained high vapor concentrations of a chlorinated solvent such as methylene chloride. 

Carbon tetrachloride is toxic by inhalation of its vapor and oral intake of the Hquid. Inhalation of the vapor constitutes the principal ha2ard. Exposure to excessive levels of vapor is characterized by two types of response an anesthetic effect similar to that caused by compounds such as diethyl ether and chloroform and organic injury to the tissues of certain organs, in particular the Hver and kidneys. This type of injury may not become evident until 1—10 days after exposure. The nature of the effect is deterrnined largely by the vapor concentration but the extent or severity of the effect is deterrnined principaHy by the duration of exposure (38). 

Toxicity. 1,1-Dichloroethane, like all volatile chlorinated solvents, has an anesthetic effect and depresses the central nervous system at high vapor concentrations. The 1991 American Conference of Governmental Industrial Hygienists (ACGIH) recommends a time-weighted average (TWA) solvent vapor concentration of 200 ppm and a permissible short term exposure level (STEL) of 250 ppm for worker exposure. The oral LD q of... 

Dichloroethane is one of the more toxic chlorinated solvents by inhalation (49). The highest nontoxic vapor concentrations in chronic exposure studies with various animals range from 100 to 200 ppm (50,51). 1,2-Dichloroethane exhibits a low single-dose oral toxicity in rats LD q is 680 mg/kg (49). Repeated skin contact should be avoided since the solvent can cause defatting of the skin, severe irritation, and moderate edema. Eye contact may have slight to severe effects. 

Entry into a tank that has contained any chlorinated or any easily evaporated solvent requires special procedures to ensure worker safety. The heavier vapors tend to concentrate in unventilated spaces. The proper tank entry procedure requires positive ventilation, testing for residue solvent vapor and oxygen levels, and the use of respiratory equipment and rescue harness. Monitoring the tank from outside is also important. The use of an appropriate gas mask is permissible in vapor concentrations of less than 2% and when there is no deficiency of atmospheric oxygen, but not for exposures exceeding one-half hour. Skin exposure to 1,1,1-trichloroethane can cause irritation, pain, bHsters, and even burning. Eye exposure may produce irritation, but should... 

Dichloroethylene is toxic by inhalation and ingestion and can be absorbed by the skin. It has a TLV of 200 ppm (10). The odor does not provide adequate warning of dangerously high vapor concentrations. Thorough ventilation is essential whenever the solvent is used for both worker exposure and flammabihty concerns. Symptoms of exposure include narcosis, dizziness, and drowsiness. Currently no data are available on the chronic effects of exposure to low vapor concentrations over extended periods of time. 

Trichloroethylene is acutely toxic, primarily because of its anesthetic effect on the central nervous system. Exposure to high vapor concentrations is likely to cause headache, vertigo, tremors, nausea and vomiting, fatigue, intoxication, unconsciousness, and even death. Because it is widely used, its physiological effects have been extensively studied. 

Victims of overexposure to trichloroethylene should be removed to fresh air, and medical attention should be obtained immediately. A self-contained positive pressure breathing device should be used wherever high vapor concentrations are expected, eg, when cleaning up spills or when accidental releases occur. 

The distinctive odor of trichloroethylene may not necessarily provide adequate warning of exposure, because it quickly desensitizes olfactory responses. EataUties have occurred when unprotected workers have entered unventilated areas with high vapor concentrations of trichloroethylene or other chlorinated solvents. Eor a complete description of proper entry to vessels containing any chlorinated solvent, see ASTM D4276-84, Standard Practice for Confined Area Entry (34). 

Overexposure to tetrachloroethylene by inhalation affects the central nervous system and the Hver. Dizziness, headache, confusion, nausea, and eye and mucous tissue irritation occur during prolonged exposure to vapor concentrations of 200 ppm (15). These effects are intensified and include incoordination and dmnkenness at concentrations in excess of 600 ppm. At concentrations in excess of 1000 ppm the anesthetic and respiratory depression effects can cause unconsciousness and death. A single, brief exposure to concentrations above 6000 ppm can be immediately dangerous to life. Reversible changes to the Hver have been reported foUowing prolonged exposures to concentrations in excess of 200 ppm (16—22). Alcohol consumed before or after exposure may increase adverse effects. 

No teratogenic effects were observed in mice and rats exposed to vapor concentrations of 300 ppm. Exposure levels having no effect on the mother are not anticipated to affect the fetus (36). 

Because chloroprene is a flammable, polymerisable Hquid with significant toxicity, it must be handled with care even in the laboratory. In commercial quantities, precaution must be taken against temperature rise from dimerisation and polymerisation and possible accumulation of explosive vapor concentrations. Storage vessels for inhibited monomer require adequate cooling capacity and vessel pressure rehef faciUties, with care that the latter are free of polymer deposits. When transportation of monomer is required, it is loaded cold (< — 10° C) into sealed, insulated vessels with careful monitoring of loading and arrival temperature and duration of transit. 

Ethyl alcohol is a flammable Hquid requiring a red label by the DOT and Coast Guard shipping classifications its flash point is 14°C (Tag, closed cup). Vapor concentrations between 3.3 and 19.0% by volume in air are explosive. Liquid ethyl alcohol can react vigorously with oxidi2ing materials. Ethyl alcohol has found wide appHcation in industry, and experience shows that it is not a serious industrial poison (273—275). If proper ventilation of the work environment is maintained, there is Httle likelihood that inhalation of the vapor will be ha2ardous. 

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