AWS F3.2:2018 pdf download.Ventilation Guide for Weld Fume
4. Occupational Exposure Limits
The need to prevent unacceptable airborne contaminant exposures in the workplace environment is most often the impe-tus behind the deployment of ventilation systems. Ultimately, it is likely that the effectiveness of those ventilation sys-tems will be judged more by the extent to which airborne contaminant exposures are maintained or controlled to levels below specific occupational exposure limits than by their ability to meet targeted system performance characteristics.Regulations related to contaminant and other exposures in the workplace tend to be performance based and compliance is determined by taking measurements of employee exposure levels and comparing them to occupational exposure lim-its. Therefore, it is crucial that those involved in decisions related to the selection or application of ventilation systems understand the fundamental concepts related to occupational exposure limits.
4.1 Permissible Exposure Limits. Permissible Exposure Limits (PELs) are regulatory values in the U.S. and are pub-lished by the Occupational Safety and Health Administration (OSHA). PELs are enforceable to protect workers against the potential health effects of overexposure to hazardous substances. PELS are regulatory limits on the amount or con-centration of a substance in the air, expressed in terms of an averaged 8-hour exposure period or 8 Hour Time-Weighted Average (TWA). OSHA also designates compounds requiring engineering and other controls to prevent skin exposures.PELs can be found in 29 CFR 1910. 1000, Tables Z-1, Z-2, and Z-3, and references within. Some states have their own occupational safety and health programs, so state exposure limits may differ, but they must be at least as stringent as the federal OSHA limits.
OSHA has established other types of exposure limits. The Short Term Exposure Limit (STEL) is expressed in terms of a concentration averaged over a 15-minute interval. A Ceiling Limit (C) indicates a level of exposure which may not be exceeded at any time, regardless of duration. Action Levels, designated for certain substances, are the levels where cer-tain required activities such as exposure monitoring and medical surveillance are required. It is important to understand that specific contaminants may have one or more of these limits associated with them.
4.2 Threshold Limit Values. The ACGIH (American Conference of Governmental Industrial Hygienists) is an indepen-dent, not-for-profit, nongovernmental corporation. The ACGIH members review published studies and scientific litera-ture to make recommendations and establish Threshold Limit Values (TLVs2) and Biological Exposure Indices (BEIs2).The ACGIH states that the TLVs formulate a conclusion, based on available information, as to the level of exposure that nearly all workers can experience repeatedly without adverse health effects. The ACGIH establishes TLVs and BEIs for the practice of industrial hygiene and they are not intended to indicate a fine line between safe and unsafe exposures.They represent the opinion of the scientific community that has reviewed the data described in the documentation, that exposure at or below the level of the TLV does not create an unreasonable risk of disease or injury. TLVs and BEIs are not standards.AWS F3.2 pdf download.