Time-weighted average employees, exposure

The purpose of the air contaminants standards are to reduce risk of occupational illness for workers by reducing permissible exposure limits (PEL) for chemicals. Table 14.10.3 lists the PELs [8-hr time-weighted average (TWA) exposure] for the solvents discussed. To achieve complianee with the PEL, administrative or engineering controls must first be determined and implemented, whenever feasible. When such controls are not feasible to achieve full eompliance, personal protective equipment, work practices, or any other protective measures are to be used to keep employee exposure below the PEL. 

Evaiuation of 8-hour Exposure Measurements taken for the purpose of determining time-weighted average (TWA) exposures are best taken with samples covering the full shift. Samples collected must be taken from the employee s breathing zone air. 

Hearing conservation record Employee s audiometric record that includes name, age, job classification, time-weighted average (TWA) exposure, date of audiogram, and name of audiometric technician. It is to be retained for the duration of employment for OSHA and kept indefinitely for workers compensation. 

OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 1 ppm for vinyl 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. Additionally, there shall not be exposure to concentrations greater than 5 ppm averaged over any period not exceeding 15 minutes. A complete standard describing control of employee exposure to vinyl chloride as required by OSHA is given in 29 CFR 1910.1017 [2]. 

The U.S. Department of Labor (OSHA) has ruled that an employee s exposure to dimethyl acetamide in any 8-h work shift of a 40-h work week shall not exceed a time-weighted average of 10 ppm DMAC vapor in air by volume or 35 mg/m in air by weight (7). If there is significant potential for skin contact with DMAC, biological monitoring should be carried out to measure the level of DMAC metaboHtes in urine specimens collected at the end of the shift. One industrial limit is 40 ppm DMAC metaboHtes, expressed as AJ-methylacetamide [79-16-3] for individuals, and 20 ppm metaboHte average for workers on the job (8). 

Phenol fumes are irritating to the eyes, nose, and skin. According to the National Institute for Occupational Safety and Health (NIOSH), exposure to phenol should be controUed so that no employees are exposed to phenol concentrations >20 mg/m, which is a time-weighted average concentration for up to a 10-h work day, 40-h work week. Phenol is very toxic to fish and has a nearly unique property of tainting the taste of fish if present in marine... 

The U.S. Department of Labor (OSHA) has ruled that an employee s exposure to aniline in an 8-h work shift of a 40-h work week shaU not exceed an 8-h time-weighted average (TWA) of 5 ppm vapor in air. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a... 

As an example, several air samples collected during an 8-hour work shift for benzene (8-hour time-weighted average = 10 ppm) were 3 hours at 4 ppm, 1 hour at 15 ppm, 2 hours at 6 ppm and 2 hours at 9 ppm. The employee s time-weighted average exposure would be ... 

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... 

OSHA requires employers of workers who are occupationally exposed to -hexane to institute engineering controls and work practices to reduce and maintain employee exposure at or below permissible exposure limits (PELs). The employer must use controls and practices, if feasible, to reduce exposure to or below an 8-hour time-weighted average (TWA) of 500 ppm (1,800 mg/m3) (OSHA 1974). The PEL for -hexane was to have been lowered to 50 ppm in 1989 however, a U S. Court of Appeals decision overturned a number of PELs promulgated in 1989, including that for -hexane. The PEL in force prior to this decision (500 ppm) is currently in effect. 

Temperature and humidity is controlled to minimize evaporation of reagents and to keep performance of electronic equipment optimal. Ventilation is adequate for the removal of noxious fumes and odors. Formaldehyde and xylene vapor concentrations must be below maximum permissible levels. For formaldehyde, this level is 0.75 ppm for an 8-h time-weighted average, or 2.0 ppm for a 15-min short-term exposure. For xylene, the level is 100 ppm for an 8-h time-weighted average and 200 ppm for a 15-min short-term exposure. The monitoring of the work area and employees can be performed on a yearly basis. Chemical and biological safety cabinets are checked for proper airflow on a yearly basis. 

An exposure-related increase in serum bilirubin was observed in workers exposed to dichloromethane, but no other sign of liver injury or haemolysis was reported (Ott et al., 1983a). A cross-sectional study of 24 employees at a fibre production plant showed no excess of electrocardiographic abnormalities among those exposed to 60-475 ppm [208-1650 mg/m ] (time-weighted average) dichloromethane and monitored for 24 h (Ott etal., 1983b). 

A longitudinal study was conducted in 10 forestry employees and six unexposed men in Colorado, United States, with an exposure time of approximately six weeks. Spenn velocity decreased in all 10 exposed men and in only two unexposed men. Semen volume was also decreased. The time-weighted average exposure of these men was 60 ppb [0.46 mg/m ] with peak exposures in the order of 2165 ppb [16.6 mg/m ]. The authors suggested that the exposure may have effected the accessory sex glands and that ethylene dibromide may have multiple sites of action (Schrader et al., 1988). 

Health and Safety Factors. Some of the Vazo products are mild skin or eye irritants in laboratory animals (Table 9) but none are skin sensitizers. In the absence of a polymerizable vinyl polymer, tetramethylsuccinonitrile [3333-52-6] (TMSN) is the principal decomposition product of Vazo 64. TMSN is highly toxic orally (rat oral LD50 of 39 mg/kg) and by inhalation (29). OSHA regulations require that an employee s exposure to TMSN in any 8-h shift does not exceed an 8-h time-weighted average of 0.5 ppm in air (=3 mg/m3). Because both TMSN solid and vapor are capable of penetrating the skin and mucous membranes, control of vapor inhalation alone may not be sufficient to prevent absorption of an excessive dose. 

---