PRINCIPLES OF TOXICOLOGY

548 CONTROLLING OCCUPATIONAL AND ENVIRONMENTAL HEALTH HAZARDS
those of the cans. In short, acceptable TWA sampling results can be obtained at low cost by using bags
followed by on-site analysis using short-term detector tubes.
The results of the sampling in all three plants showed that the highest concentrations were found
in the holding coolers, and that they can exceed the IDLH level of 50,000 ppm. In one plant, workers
spent 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 inside
was relatively short. Ventilation in both areas was relatively poor, since incursion of fresh outdoor air
was minimized to maintain proper refrigeration.
The rate of generation of carbon dioxide gas from dry ice in these settings is dependent upon a
number of variables, including the quantity of dry ice present, the temperature, the degree of outdoor
air infiltration, the size of the room, and the length of time the meat packages are held before being
loaded onto trucks. Table 22.4 shows that exposures can be highly variable when measuring concentrations
with 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 the
allowable levels were commonplace.
Several control alternatives were considered. Substitution of other methods of quick freezing offer
the best method of controlling the hazard, since no carbon dioxide is present. Freeze tunnels or blast
tunnels 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, since
no refrigerant is present inside the package itself. Nitrogen poses the potential hazard of displacement
of oxygen, although it is preferable to carbon dioxide, since it poses no toxicity other than acting as
an asphyxiant. The chief drawback to blast tunnels is that they occupy a great deal of floor space, and
are thus difficult to fit into existing facilities. Spiral tunnels, which occupy less floor space are now
available.
Another control method involves the use of local exhaust ventilation to exhaust fugitive carbon
dioxide emissions from the machines that deliver the dry ice (which actually is applied in a pressurized
liquid form) to the poultry package. Determination of the adequacy of the exhaust ventilation system
often can be determined visually, since the cold CO 2 gas is visible. The local exhaust systems found
in the three plants studied all had inadequate hood designs and airflow rates that failed to capture the
TABLE 22.4 Initial Short-Term Detector Tube Sampling at Four Poultry Processing Plants
Concentration (ppm)
Plant Area Number of Employees Range Average
1 Breathing zone inside freezer 9 8,000–29,000 18,000
Loading dock 2 5,000–6,500 5,750
Dry Ice delivery to poultry
packages
3 8,000–11,000 8,000
2 Holding cooler and
palletizing area
3 12,000 12,000
Loading dock 2 12,000–13,000 12,500
Dry ice delivery to poultry
packages
6 5,000–8,000 6,400
3 Holding cooler 5 23,000–60,000 33,000
Dry Ice delivery to poultry
packages (local exhaust
present)
6 2,700–5,000 3,700
4 Holding cooler 3 5,000–26,000 18,000
Palletizing area 2 11,000–30,000 21,000
Dry ice delivery to poultry
packages
4 8,000–22,000 12,000