Time-Weighted Average-Permissible Exposure Limit TWA-PEL

B. 8-Hour, Time-weighted-average, Permissible Exposure Limit (TWA PEL) ... 

OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 50 ppm (35mg/m ) for ammonia. 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]. 

OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 100 ppm for methyl chloride. 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. In addition, OSHA lists an acceptable ceiling concentration of 200 ppm for methyl chloride. The acceptable ceiling concentration is the exposure limit that shall not be exceeded at any time during an 8-hour shift. Methyl chloride has an exception in that it has an acceptable maximum peak above the acceptable ceiling concentration of 300 ppm for an 8-hour shift as long as the maximum duration is only once for 5 minutes in any hour [3]. 

Exposure Monitoring — Your employer must measrae yora exposure to airborne MC. To help keep you from being overexposed, OSH A has set exposure hmits for MC. These exposrae limits are (1) 25 ppm as an 8-hour Time Weighted Average Permissible Exposrae Limit (TWA/PEL), or 125 ppm as a 15-minute Short Term Exposiae Limit (STEL). 

In the working environment, a principal concern is to ensure that the exposure to elemental phosphorus in air is kept below O.lmg/m, which is the time weighted average permissible exposure limit for workers (TWA, PEL)... 

The American Conference of Governmental Industrial Hygienists threshold limit value (ACGIH TLV), the National Institute for Occupational Safety and Health recommended exposure limit (NIOSH REL), and the Occupational Safety and Health Administration permissible exposure limit (OSHA PEL) for ethyl acetate are 400 ppm. Both the ACGIH TLV and OSHA PEL are 8 h time-weighted average (TWA) while the NIOSH REL is a 10 h TWA. 

For worker exposure to trichloroethylene vapor, OSHA set a maximum eight-hour time-weighted average (TWA) concentration of 100 ppm. This severely restricted certain appHcations, and many organizations converted to other chlorinated solvents. As a result, U.S. production of trichloroethylene declined about 70% from a peak in 1970 (Table 2). In 1989, OSHA lowered the permissible exposure limit (PEL) from 100 ppm eight-hour TWA to 50 ppm eight-hour TWA (33). This added further pressure for some users to consider changing to alternative solvents. 

Workplace. The Occupational Safety and Health Administration (OHSA) has estabUshed workplace permissible exposure limits (PEL) for chromium metal and three forms of chromium compounds. OSHA s PEL for chromic acid and chromates is 0.1 mg/m 3 both a ceiling, ie, no exposure above this concentration is allowed, and an 8-h time-weighted average (TWA). Chromium metal and insoluble chromium salts have an 8-h TWA PEL of 1.0 mg/m Cr, and the same standard is 0.5 mg/m Cr for soluble Cr(III) and Cr(II) compounds (144). 

EL = emissions level ERA = Environmental Protection Agency HSDB = Hazardous Substances Data Bank lARC = International Agency for Research on Cancer IRIS = Integrated Risk Information System NIOSH = National Institute of Occupational Safety and Health OEL = occupational exposure limit OSHA = Occupational Safety and Health Administration PEL = permissible exposure limit RAC = reference air concentration REL = recommended exposure limit RCRA = Resource Conservation and Recovery Act RfD = reference dose TLV = threshold limit value TWA = time-weighted average WHO = World Health Organization... 

OSHA = Occupational Safety and Health Administration PAGs = protective action goals PEL = permissible exposure limit S = soluble REL = recommended exposure limit TWA = time-weighted average... 

PEL Pg pmol PHS PMR ppb ppm ppt REL RfD RTECS sec SCE SIC SIR SMR STEL STORET TLV TSCA TRI TRS TWA u.s. UF yr WHO wk permissible exposure limit picogram picomole Public Health Service proportionate mortality ratio parts per billion parts per million parts per trillion recommended exposure limit Reference Dose Registry of Toxic Effects of Chemical Substances second sister chromatid exchange Standard Industrial Classification Standardized incidence ratio standard mortality ratio short term exposure limit STORAGE and RETRIEVAL threshold limit value Toxic Substances Control Act Toxics Release Inventory total reduced sulfur time-weighted average United States uncertainty factor year World Health Organization week... 

OSHA requires employers of workers who are occupationally exposed to a toxic or hazardous substance to institute engineering controls and work practices that maintain or reduce their exposure to a level that is at or below the permissible exposure limit (PEL) established for the substance. For occupational exposures to lead, the employer must use engineering controls and work practices to achieve an occupational exposure of 50 pg/nr3 (0.006 ppm) or lower, based on an 8-hour time-weighted average (TWA) (OSHA 1995). When employee exposures to lead can not be maintained at or below 50 pg/rn3... 

TIN-TWA Threshold limit value, time-weighted average for 8-h exposures, with ceiling concentrations shown as C, and with skin absorption hazard as S. The OSHA permissible exposure limit (PEL) is the lower of the TWA or the ceiling limit. 

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