Industrial Ventilation: A Manual of Recommended Practice, 23rd Edition

from intro: The importance of clean uncontaminated air in the industrial work environment is well known. Modern industry with its complexity of operations and processes uses an increasing number of chemical compounds and substances, many of which are highly toxic. The use of such materials may result in particulates, gases, vapors, and/or mists in the workroom air in concentrations that exceed safe levels. Heat stress can also result in unsafe or uncomfortable work environments. Effective, well-designed ventilation offers a solution to these problems where worker protection is needed. Ventilation can also serve to control odor, moisture, and other undesirable environmental conditions. The health hazard potential of an airborne substance is characterized by the Threshold Limit Value (TL V*). The TLV refers to the airborne concentration of a substance and repre¬sents conditions under which it is believed that nearly all workers may be exposed day after day without adverse health effects. The time-weighted average (TWA) is defined as the time-weighted average concentration for a conventional 8-hour workday and a 40-hour workweek which will produce no adverse health effects for nearly all workers. The TLV-TWA is usually used to determine a safe exposure level. TLVs are published annually by the American Conference of Governmental Industrial Hygienists (ACGIH); revisions and additions are made regularly as information becomes avail¬able. Appendix A of this Manual provides the current TLV list for chemical substances as of the date of publication. Ventilation systems used in industrial plants are of two generic types. The SUPPLY system is used to supply air, usually tempered, to a work space. The EXHAUST system is used to remove the contaminants generated by an operation in order to maintain a healthful work environment....