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SAN JOAQUIN DELTA COLLEGE This last factor required knowledge of body enzymes that may be stimulated or depressed, which then causes rapid or delayed elimination of given chemical Description of Exposure In order to better described the administered dose reported in the literature, six abbreviations are used These terms indicate whether the dose caused death (LD) or other toxic effects (TD) and whether it was administered as a lethal concentration (LC) or toxic concentration (TC)in the inhaled air In general,the term "Lo" is used where the number from the population or the calculated percentage of subjects showing an effect was listed as 100 The definition of terms is as follows TDLo-Toxic Dose Low-the lowest dose of a substance introduced by any routs, other than inhalation, over any given period of time and reported to produce any toxic effect in humans or to produce carcinogenic, neoplastigenic, or teratogenic effects in animals or humans TCLo - Toxic Concentration Low - the lowest concentration of a substance in air to which humans or animals have been exposed for any given period of time that has produced any toxic effect in humans or produced a carcinogenic, neoplastigenic, or teratogenic effect in animals or humans LDLo - Lethal Dose Low - the lowest dose (other than LD50) of a substance introduced by any route, other than inhalation, over any given period of time in one or more divided portions and reported to have caused death in humans or animals LD50 - Lethal Dose Fifty- a calculated dose of a substance which in expected to cause the death of 50% of an entire defined experimental animal population It is determined from the exposure to the substance by any route other than inhalation of a significant number from that population Other lethal dose percentages, such as LD1, LD10, LD30, and LD99, may be published in the scientific literature for the specific purposes of the author Such data would be published if these figures, in the absence of a calculated lethal dose(LD50),were the lowest found in the literature LCLo - Lethal Concentration Low - the lowest concentration of a substance in air, other than LC50, which has been reported to have caused death in humans or animals The reported concentrations may be entered for periods of exposure which are less than 24 hours(acute)or greater that 24 hors(subacute and chromic) LC50-Lethal Concentration Fifty- A calculated concentration of a substance in air, exposure to which for a specified length of time is expected to cause the death of 50% of an entire defined experimental animal population It is determined from the exposure to the substance of a significant number from that population Ventilation - Dilution ventilation is used pnmanly to control vapors and gases which mix readily and uniformly with the workroom air and whose rate of evolution is relatively constant and can be readily determined It is rarely applied to the control of particulate matter such as dust, fumes, and mists since these do not mix uniformly and their rate of evolution is usually impossible to ascertain In some instances,empirical data for fume or mist control by dilution are available One such case is black iron or mild steel welding where cfn dilution rates have been set up on the basis of number of welders in a workroom and size of welding rod used Calculation of Dilution Ventilation Rates One method of calculating cfin dilution rates involves a knowledge of prevailing conditions during normal operations if tests can be made to determine the actual concentration of contaminant and the rate of natural infiltration of air into the workroom during existing conditions, the required dilution ventilation will be found by the following formula Equation I i Dilution(CFM)=Prevailing Concentration(ppm)X Infiltration(cfm)X K/TLV(ppm) where TLV=the threshold limit value K=a factor of safety(see Table below) K Factors At Different Distribution Conditions Toxicity Poor Average Good Excellent Pogo #8