exposure threshold has been adopted to account for the acute effects of substances that have primarily chronic affects. Threshold Limit Value Ceiling (TLV-C): This is the concentration that should not be exceeded during – any part of the working exposure. Peak exposures should be always controlled. For substances that do not have TLV-TWA or TLV-C established, the maximum admissible peak concentrations must not exceed: Three-times the value of the TLV-TWA for no more than 15 minutes, no more than four times per workday. Exposures must be at least 1 hour apart during the workday. Five times the TLV-TWA under any circumstances. Action Level: is the level of exposure to a hazardous substance at which an employer must take the required precautions to protect the workers; it is normally one-half of the permissible exposure limit. The of measures for the threshold limit values are ppm and mg/m3. The TLVs for aerosols are expressed usually in mg/m3. The TLVs for gases and vapors are expressed in ppm or mg/m3. An exposure rating is assigned to each chemical and activity pair. Where air monitoring results are available, the weekly time weighted average exposure may be estimated using the following equation: Where: E = weekly exposure (ppm or mg/m3) F = frequency of exposure per week (no. per week) M = magnitude of exposure (ppm or mg/m3) W = average working hours per week (40 hours) D = average duration of each exposure (hours) Table . Calculating the exposure rating when PEL (OEL or TWA) data is available Exposure Rating E / PEL (ER) 1 < 0.1 2 0.1 to < 0.5 3 0.5 to < 1.0 4 1.0 to < 2.0 5 2.0 ≥
exposure threshold has been adopted to account for the acute effects of substances that have primarily chronic affects. Threshold Limit Value – Ceiling (TLV-C): This is the concentration that should not be exceeded during any part of the working exposure. Peak exposures should be always controlled. For substances that do not have TLV-TWA or TLV-C established, the maximum admissible peak concentrations must not exceed: Three-times the value of the TLV-TWA for no more than 15 minutes, no more than four times per workday. Exposures must be at least 1 hour apart during the workday. Five times the TLV-TWA under any circumstances. Action Level: is the level of exposure to a hazardous substance at which an employer must take the required precautions to protect the workers; it is normally one-half of the permissible exposure limit. The of measures for the threshold limit values are ppm and mg/m3. The TLVs for aerosols are expressed usually in mg/m3. The TLVs for gases and vapors are expressed in ppm or mg/m3. An exposure rating is assigned to each chemical and activity pair. Where air monitoring results are available, the weekly time weighted average exposure may be estimated using the following equation: Where: E = weekly exposure (ppm or mg/m3) F = frequency of exposure per week (no. per week) M = magnitude of exposure (ppm or mg/m3) W = average working hours per week (40 hours) D = average duration of each exposure (hours) Table . Calculating the exposure rating when PEL (OEL or TWA) data is available Exposure Rating (ER) E / PEL 1 < 0.1 2 0.1 to < 0.5 3 0.5 to < 1.0 4 1.0 to < 2.0 5 ≥ 2.0
Risk-Assessment_Guide_Chem.docx