Exposure continued level, time-weighted

TLV The TLV or Threshold Limit Value refers to a safe level of exposure by inhalation. The definition was established by the American Conference of Governmental Hygienists. There are several variations or criteria levels for the TLV. As an example, hydrogen sulfide has a TLV for short-term exposure limits (STEL) of 15 minutes of only 5 ppm. Comparing this to the TLV-STEL of 400 ppm for carbon monoxide provides an indication of the need to be extremely careful when H2S is suspected. Under OSHA Standards, and particularly on MSDS (Material Safety Data Sheets) compounds are associated with a time weighted average (TWA) TLV, which is the allowable concentration for an 8-hour continuous exposure period. For firefighting purposes, the short-term exposure is likely more realistic. 

OELs are expressed either as parts per million (ppm) volume/volume or as mg/m, and are related to a time reference period (e.g. 8h Time Weighted Average (TWA) or 15 min Short Term Exposure Limit (STEL)). They do not provide a rigid dividing line between safe and unsafe conditions and it is good practice to maintain exposure as low as reasonably practicable below the limit. Exposures measured as described earlier may be compared with these limits and a decision taken on whether exposure is satisfactorily low or whether further exposure reduction is necessary. Exposure should be monitored with a frequency depending on its likely variability and the extent to which it is below the relevant OEL. Continuous monitoring of exposure is rarely required. It is important to remember that for substances with a SKIN notation the OEL is only valid as a level likely to be sufficiently low to protect health when adequate precautions have been taken to prevent skin exposure. 

Administer a continuing, effective hearing conservation program IF employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) OR equivalently, a dose of fifty percent. 

Research on the long-term effects of low-level pollution continues. Air pollution by ozone, sulfur dioxide, and particulates in Britain kills 24,000 people annually.58 It is estimated that exposure to diesel exhaust over a 70-year lifetime will cause 450 cases of cancer per million people in California.59 Epidemiologists continue to investigate clusters of diseases such as the two to four times higher incidence of neural tube and certain heart defects in children born within A mile of Superfund sites in California,60 the lower birth weight and prematurity of infants born to... 

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