PRINCIPLES OF TOXICOLOGY

top, and numerous slots with smaller widths at the top than at the bottom were placed in the hood to
make the airflow more uniform throughout the work area. The floor fan was removed to eliminate
cross-flow, which would increase turbulence and reduce the capture efficiency of the hood. Workers
were instructed and required to wear synthetic rubber gloves to minimize hand contact with the styrene
and reduce the need to use acetone to clean the hands. Exposures in the area had been reduced to less
than 40 ppm as a result of these measures.
Exposure to Carbon Dioxide in a Meat-Processing Industry
22.4 CASE STUDIES 547
The rapidly growing demand for meat products in the fast-food industry has resulted in an increased
use of dry ice (solid carbon dioxide) in many meat-processing plants. Contrary to conventional wisdom,
carbon dioxide is not a harmless substance. It can cause a variety of health problems at relatively high
exposure levels. If exposures are high enough, the results can be fatal.
The toxicity of carbon dioxide is fairly well established. It has been classified as both a stimulant
and depressant of the central nervous system, an asphyxiant, and a potent respiratory stimulant. Rapid
breathing, increased heart rate, headache, sweating, visual disturbances, convulsions, and death are
among the symptoms related to carbon dioxide overexposure. The gas can be weakly narcotic at 30,000
ppm, and intoxication can be produced by a 30-min exposure to 50,000 ppm. Because of the extreme
sensitivity of various chemoreceptors to CO 2 , its high solubility in tissue fluids (20 times that of
oxygen), and the permeability of the blood–brain barrier to CO 2 , the effects on the respiratory and
central nervous systems are rapid.
Carbon dioxide poisonings have been reported in aircraft transporting frozen food, meat-processing
plants, farm silos, fermentation tanks, shipping, mining, and firefighting. Both the OSHA PEL and
1993-4 ACGIH TLV ® are 5000 as an 8-h TWA. The “immediately dangerous to life and health” level
set by NIOSH is 50,000 ppm.
This study describes an occupational hygiene study in three different meat-processing plants, which
used dry ice to refrigerate packages, and documents how a change in production techniques (i.e., the
increased use of dry ice) resulted in a significant health hazard and how the hazard can be controlled.
Preliminary interviews with workers and managers revealed that several workers had been hospitalized
for dizziness, hyperventilation, vomiting, and headaches. The interviews also revealed that the amount
of dry ice used from one day to another varied greatly. Scheduling the full-day survey so that
representative worst-case exposure levels would be obtained proved to be difficult.
Levels of exposure to carbon dioxide were initially determined with short-term detector tubes. Care
was taken not to include exhaled air while sampling inside workers’ breathing zones, since exhaled
breath can contain as much as 59,000 ppm carbon dioxide. Normal outdoor air contains about 350–400
ppm of carbon dioxide.
The short-term detector tubes were used to determine where full-shift samples were needed. The
8-h TWA was determined using a bag sampling procedure and gas chromatography (NIOSH Analytical
Method 5249). A previous attempt to measure TWA exposures using long-term detector tubes showed
that the color change was not distinguishable from the background color of the medium. Therefore,
long-term detector tubes were rejected as an analytical method for this study. The manufacturer of the
long-term detector tubes was notified of the findings.
Samples were collected in Tedlar bags at a nominal flow rate of 20 cm 3 /min. The concentration in
the bag was determined in three ways: (1) short-term detector tubes were used to measure the
concentration of CO 2 inside the bag, (2) an aliquot from the bag was transferred to a vacuum sampler
and then shipped to the laboratory (this was considered necessary because of the possibility of bag
breakage during shipment to the lab), and (3) finally, the bags themselves were shipped and analyzed.
On return, the bags were checked for leaks, which were found to be common.
Generally, the direct analysis of the bags in the laboratory gave the lowest results, perhaps because
of leakage during shipment. Laboratory analysis of the Vacu-Sampler cans gave the highest results.
On-site analysis of bag air using short-term detector tubes gave results that were only slightly less than