TWA values

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. 

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. 

Barium metal and most barium compounds are highly poisonous. A notable exception is barium sulfate which is nontoxic because of its extreme iasolubihty ia water. Barium ion acts as a muscle stimulant and can cause death through ventricular fibrillation of the heart. Therefore, care must be taken to avoid contact with open areas of the skin. Workers must wear respirators (of type approved for toxic airborne particles), goggles, gloves, and protective clothing at all times. The toxic barium aluminate residue obtained from barium production is detoxified by reaction with a solution of ferrous sulfate and converted iato nontoxic barium sulfate. According to OSHA standards, the TWA value for Ba and Ba compounds ia air is 0.5 mg/m. ... 

Trichloroethane is much more toxic than 1,1,2-trichloroethane in acute exposure studies (108). The 1991 ACGIH recommended TWA value for... 

Once the dispersion calculations are completed, the question arises What concentration is considered dangerous Concentrations based on TLV-TWA values, discussed in chapter 2, are overly conservative and are designed for worker exposures, not short-term exposures under emergency conditions. 

After all data has been compiled to show TWA values this information is then shared with employees using a computerized employee exposure form. This concludes the task of dust measurement by means of the standardized vertical elutriator method. 

We have already been introduced to polyurethane chemistry in Chapter 10, Section 2, where we used toluene diisocyanate (TDI) reacting with a diol to give a polyurethane. Polyurethanes derived from MDI are more rigid than those from TDI. New applications for these rigid foams are in home insulation and exterior autobody parts. The intermediate MDA is now on the Reasonably Anticipated to Be Human Carcinogens list and the effect of this action on the market for MDI remains to be seen. The TLV-TWA values for MDA and MDI are some of the lowest of the chemicals we have discussed, being 0.1 and 0.005 ppm respectively. 

TWA Values for Selected Monomers and Additional Recognized Toxins... 

Table I summarizes the values of the AL and the PEL listed by OSHA for the five chemicals previously mentioned. In each standard, the scheme is essentially the same as described, although the required frequency of monitoring varies. Significantly, all of these chemicals are chronic-exposure hazards and decisions are based upon PELs which are 8-hr TWA values. It is implied...

Perhaps the ultimate failing of the 0SHA/NI0SH scheme is that it bases important decisions on relatively small amounts of data. Intuitively, such a scheme would lead to incorrect conclusions in many cases. Table III gives the number of samples expected to be required for making decisions in various environments (calculated from the relationship derived in the appendix). As in the previous example the PEL is 10 and the AL is 5. In virtually all cases the number of samples is two or less. With such small sample sizes accurate prediction of the long-term rates of exposure is impossible without additional information or assumptions. Stated in slightly different terms, the interday variability of 8-hr TWA values cannot be measured or controlled for with information based strictly on such small sample sizes. 

TLV-TWA is the Threshold Limit Value—time weighted average concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effect (ACGIH 2001). In general, TLV-TWA values are used to derive BEIs (Biological Exposure Indices). 

When considering toxicity manifestation time and vapor dispersion, the detection sensitivity for vapor concentration is one hundredth of LCtso within 1 min. In the case of GB, this required detection sensitivity is 0.15 mg/m, and at this level there is no odor and humans show no signs of toxicity. In the chemical weapon disposal situation, because the workers stay in one place for a long time, the time weighted average (TWA) values are the monitoring target for allowed operational conditions. These TWA values are approximately 1/100,000 of LCtso. The desired alarm time is to be less than several minutes. There is a trade-off relationship between LOD, alarm time, detection accuracy and... 

Lead (blood - women 5-aminolevulinic acid urine, Davies method women <45 years TLV-TWA value (lead)... 

Additionally the TRK value/TLV-TWA value for chromium(VI) compounds of 0.05 mg rrT calculated as Cr03 in total dust has to be complied with [3.137]. 

US OSHA permissible exposure limit (PEL) time-weighted average (TWA) value of 0.1 ppm (0.25 mg m ) short-term exposure limit (STEL) value of 0.3 ppm (0.8 mg m ), not to exceed 15 min. 

AIHA established a committee to develop WEELs for chemicals which have no current exposure guidelines established by other organizations. There are two WEEL limits for most materials. The first is an 8 h TWA value similar to ACGIH TLV - TWA values. The second, which is only available for a limited number of cases, is a short-term TWA for exposure of either I or 15 min duration. 

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