TWA

Health and Safety Factors. See "General Health and Safety Eactors." The following toxicides for adiponitrile have been reported oral LD q (rats), 300 mg/kg dermal LD q (rabbits), 2,134 mg/kg and inhalation 4-h LC q (i ts), 1.7 mg. NIOSH has proposed an exposure limit of 4 ppm as a TWA (68). 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

Material Safety Data Sheets (MSDS) issued by suppHers of acetone ate requited to be revised within 90 days to include new permissible exposure limits (PEL). Current OSHA PEL (54) and ACGIH threshold limit values (TLV) (55) ate the same, 750 ppm TWA and 1000 ppm STEL. Eot comparison, the ACGIH TWA values for the common mbbing alcohols are ethyl, 1000, and isopropyl, 400 ppm. A report on human experience (56) concluded that exposure to 1000 ppm for an 8-h day produced no effects other than slight, transient irritation of the eyes, nose, and throat. 

Current TLV/TWA values are provided in Matena/Safety Data Sheets provided by manufacturers upon request. Values for 1989 (83,107) appear in Table 5. 

Exposure limits for siHcon carbide and powders of zirconium compounds (including zirconium dioxide) have been estabHshed by ACGIH. TLV—TWA s are 10 mg/m and 5 mg/m, respectively. OSHA guidelines for zirconium compounds call for a PEL of 5 mg/m. There are no exposure limits for siHcon nitride powder, but pmdent practice suggests a TLV—TWA of 0.1 mg/m. The soHd ceramics present no apparent health hazard. In machining such ceramics, however, care should be taken to prevent inhalation of respirable particles in amounts in excess of estabHshed limits. Disposal should be in approved landfills the materials are inert and should pose no danger to the environment. 

The OSHA permissible exposure limit (11) and the American Conference of Governmental Industrial Hygienists (ACGIH) estabHshed threshold limit value (TLV) (12) for fluorides is 2.5 mg of fluoride per cubic meter of air. This is the TLV—TWA concentration for a normal 8-h work day and a 40-h work week. 

OSHA has a TWA standaid on a weight of Sb basis of 0.5 mg/for antimony in addition to a standard TWA of 2.5 mg/m for fluoride. NIOSH has issued a criteria document on occupational exposure to inorganic fluorides. Antimony pentafluoride is considered by the EPA to be an extremely hazardous substance and releases of 0.45 kg or more reportable quantity (RQ) must be reported. Antimony triduoride is on the CERCLA bst and releasing of 450 kg or more RQ must be reported. 

Health and Safety Factors. The low solubiUty of calcium fluoride reduces the potential problem of fluoride-related toxicity. Water saturated with calcium fluoride has a fluoride concentration of 8.1 ppm as compared to the recommended water fluoridation level of 1 ppm fluoride ion. However, because the solubiUty of calcium fluoride ia stomach acid is higher, continued oral ingestion of calcium fluoride could produce symptoms of fluorosis. The adopted TWA limit for fluorides as F is 2.5 mg/m (68,69). 

The ACGIH adopted TLV/TWA for 1992—1993 for fluorides as F is TWA 2.5 mg/m, and for cobalt as Co metal dust TWA 0.05 mg/m. Dust masks should be used while handling both the cobalt fluorides and all other cobalt compounds. CoF is shipped as an oxidizer and a corrosive material. 

The time-weighted average (TWA) concentrations for 8-h exposure to bromine ttifluoride, bromine pentafluoride, chlorine ttifluoride, chlorine pentafluoride, and iodine pentafluoride have been estabHshed by ACGIH on a fluoride basis to be 2.5 mg/m. NIOSH reports (121) the foUowing inhalation toxicity levels for chlorine ttifluoride LC q monkey, 230 ppm/h LC q mouse, 178 ppm/h for chlorine pentafluoride LC q monkey, 173 ppm /h mouse, 57 ppm/h. 

Lead fluorides are highly toxic and should be handled with great care. The ACGIH adopted toxicity value for lead compounds as Pb is TWA 0.15 mg/m and for fluorides as F 2.5 mg/m. PbF is prepared by the action of elemental fluorine on very dry Pbp2 at 280—300°C (15). 

Mercury salts are highly toxic and must be handled carefliUy. It is necessary to consult the material safety data sheet prior to handling. Strict adherence to OSHA/EPA regulations is essential. The ACGIH adopted (1991—1992) TLV for mercury as inorganic compounds is TWA 0.1 mg/m and for fluorides as F 2.5 mg/m. ... 

These salts are corrosive and are to be considered toxic because of the presence of Ag+ ions. The American Conference of Government Industrial Hygienists (ACGIH) (1992—1993) has adopted TWA values of 0.01 mg/m for silver metal and 0.01 mg/m for soluble silver salts. TWA for fluorides as F ions is 2.5 mg/m. The MSDS should be consulted prior to use. Skin contact and inhalation should be avoided. 

Health and Safety Factors. Sulfur hexafluoride is a nonflammable, relatively unreactive gas that has been described as physiologically inert (54). The current OSHA standard maximum allowable concentration for human exposure in air is 6000 mg/m (1000 ppm) TWA (55). The Underwriters Laboratories classification is Toxicity Group VI. It should be noted, however, that breakdown products of SF, produced by electrical decomposition of the gas, are toxic. If SF is exposed to electrical arcing, provision should be made to absorb the toxic components by passing the gas over activated alumina, soda-lime, or molecular sieves (qv) (56). 

Toxicity. Sulfur tetrafluoride has an inhalation toxicity comparable to phosgene. The current OSHA standard maximum allowable concentration for human exposure in air is 0.4 mg/m (TWA) (54). On exposure to moisture, eg, on the surface of skin, sulfur tetrafluoride Hberates hydrofluoric acid and care must be taken to avoid bums. One case of accidental exposure of electrical workers to decomposed SF gas containing SF has been cited (108). 

The OSHA standard maximum allowable concentration for human exposure in air is 0.10 mg/m (TWA) (55). No commercial uses for this compound have developed. 

Titanium trifluoride can be stored in tightly closed polyethylene containers for several years. Shipping regulations classify the material as a corrosive sohd and it should be handled in a fully ventilated area or in a chemical hood. The ACGIH adopted toxicity values (1992—1993) for TiF is as TWA for fluorides as F 2.5 mg/m. ... 

Although titanium compounds are considered to be physiologicaHy inert (21), fluorides in general are considered as toxic above 3 ppm level and extreme care should be taken in handling large amounts of titanium salts as weU as hexafluorotitanic acid. The ACGIH adopted (1992—1993) toxicity limits are as TWA for fluorides as F 2.5 mg/m. ... 

OSHA has a standard time-weighted average (TWA) of 2.5 mg/m based on fluoride. NIOSH has issued a criteria document (24) on occupational exposure to inorganic fluorides. 

Sources of human exposure to formaldehyde are engine exhaust, tobacco smoke, natural gas, fossil fuels, waste incineration, and oil refineries (129). It is found as a natural component in fmits, vegetables, meats, and fish and is a normal body metaboHte (130,131). FaciUties that manufacture or consume formaldehyde must control workers exposure in accordance with the following workplace exposure limits in ppm action level, 0.5 TWA, 0.75 STEL, 2 (132). In other environments such as residences, offices, and schools, levels may reach 0.1 ppm HCHO due to use of particle board and urea—formaldehyde foam insulation in constmction. 

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. 

The U.S. Occupational Safety and Health Administration (OSHA) has set a ceiling level for iodine of 0.1 ppm in air. The American Conference of Government and Industrial Hygienists (ACGIH) estabUshed 0.1 ppm as the TLV (TWA) for iodine. The maximum allowable concentration in air (MAK value) is also 0.1 ppm (104—106). 

Safety. Magnesium oxide (fume) has a permissible exposure limit (PEL) (134) (8 hours, TWA), of 10 mg/m total dust and 5 mg/m respirable fraction. Tumorigenic data (intravenous in hamsters) show a TD q of 480 mg/kg after 30 weeks of intermittent dosing (135), and toxicity effects data show a TC q of 400 mg/m for inhalation in humans (136). Magnesium oxide is compatible with most chemicals exceptions are strong acids, bromine pentafluoride, chlorine trifluoride, interhalogens, strong oxidizers, and phosphorous pentachloride. 

K. W. Reynard, ed.. Inventory ofiMaterials Designation Systems, Versailles Advanced Materials and Standards, TWA-10, National Physical Laboratory, Teddington, U.K., 1992. 

Health and Safety. Remover formulas that are nonflammable may be used in any area that provides adequate ventilation. Most manufacturers recommend a use environment of 50—100 parts per million (ppm) time weighted average (TWA). The environment can be monitored with passive detection badges or by active air sampling and charcoal absorption tube analysis. The vapor of methylene chloride produces hydrogen chloride and phosgene gas when burned. Methylene chloride-type removers should not be used in the presence of an open flame or other heat sources such as kerosene heaters (8). 

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