PRINCIPLES OF TOXICOLOGY - Biology East Borneo

548 CONTROLLING OCCUPATIONAL AND ENVIRONMENTAL HEALTH HAZARDSthose of the cans. In short, acceptable TWA sampling results can be obtained at low cost by using bagsfollowed by on-site analysis using short-term detector tubes.The results of the sampling in all three plants showed that the highest concentrations were foundin the holding coolers, and that they can exceed the IDLH level of 50,000 ppm. In one plant, workersspent nearly the entire shift working on a palletizing operation inside a relatively large holding cooler.In another plant, entry into a smaller holding cooler was confined to forklift drivers, whose time insidewas relatively short. Ventilation in both areas was relatively poor, since incursion of fresh outdoor airwas minimized to maintain proper refrigeration.The rate of generation of carbon dioxide gas from dry ice in these settings is dependent upon anumber of variables, including the quantity of dry ice present, the temperature, the degree of outdoorair infiltration, the size of the room, and the length of time the meat packages are held before beingloaded onto trucks. Table 22.4 shows that exposures can be highly variable when measuring concentrationswith short-term detector tubes. Table 22.5 shows the results of TWA exposure measurements.All workers were exposed to levels above the TLV ® of 5000 ppm, and excursions well above theallowable levels were commonplace.Several control alternatives were considered. Substitution of other methods of quick freezing offerthe best method of controlling the hazard, since no carbon dioxide is present. Freeze tunnels or blasttunnels which use low-temperature air or nitrogen can be used. The meat is frozen and then packaged;this method requires more rigorous control of temperatures inside holding coolers and trucks, sinceno refrigerant is present inside the package itself. Nitrogen poses the potential hazard of displacementof oxygen, although it is preferable to carbon dioxide, since it poses no toxicity other than acting asan asphyxiant. The chief drawback to blast tunnels is that they occupy a great deal of floor space, andare thus difficult to fit into existing facilities. Spiral tunnels, which occupy less floor space are nowavailable.Another control method involves the use of local exhaust ventilation to exhaust fugitive carbondioxide emissions from the machines that deliver the dry ice (which actually is applied in a pressurizedliquid form) to the poultry package. Determination of the adequacy of the exhaust ventilation systemoften can be determined visually, since the cold CO 2gas is visible. The local exhaust systems foundin the three plants studied all had inadequate hood designs and airflow rates that failed to capture theTABLE 22.4 Initial Short-Term Detector Tube Sampling at Four Poultry Processing PlantsConcentration (ppm)Plant Area Number of Employees Range Average1 Breathing zone inside freezer 9 8,000–29,000 18,000Loading dock 2 5,000–6,500 5,750Dry Ice delivery to poultry3 8,000–11,000 8,000packages2 Holding cooler and3 12,000 12,000palletizing areaLoading dock 2 12,000–13,000 12,500Dry ice delivery to poultry6 5,000–8,000 6,400packages3 Holding cooler 5 23,000–60,000 33,000Dry Ice delivery to poultry6 2,700–5,000 3,700packages (local exhaustpresent)4 Holding cooler 3 5,000–26,000 18,000Palletizing area 2 11,000–30,000 21,000Dry ice delivery to poultrypackages4 8,000–22,000 12,000