PRINCIPLES OF TOXICOLOGY - Biology East Borneo

22.4 CASE STUDIES 547top, and numerous slots with smaller widths at the top than at the bottom were placed in the hood tomake the airflow more uniform throughout the work area. The floor fan was removed to eliminatecross-flow, which would increase turbulence and reduce the capture efficiency of the hood. Workerswere instructed and required to wear synthetic rubber gloves to minimize hand contact with the styreneand reduce the need to use acetone to clean the hands. Exposures in the area had been reduced to lessthan 40 ppm as a result of these measures.Exposure to Carbon Dioxide in a Meat-Processing IndustryThe rapidly growing demand for meat products in the fast-food industry has resulted in an increaseduse 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 highexposure 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 stimulantand depressant of the central nervous system, an asphyxiant, and a potent respiratory stimulant. Rapidbreathing, increased heart rate, headache, sweating, visual disturbances, convulsions, and death areamong the symptoms related to carbon dioxide overexposure. The gas can be weakly narcotic at 30,000ppm, and intoxication can be produced by a 30-min exposure to 50,000 ppm. Because of the extremesensitivity of various chemoreceptors to CO 2, its high solubility in tissue fluids (20 times that ofoxygen), and the permeability of the blood–brain barrier to CO 2, the effects on the respiratory andcentral nervous systems are rapid.Carbon dioxide poisonings have been reported in aircraft transporting frozen food, meat-processingplants, farm silos, fermentation tanks, shipping, mining, and firefighting. Both the OSHA PEL and1993-4 ACGIH TLV ® are 5000 as an 8-h TWA. The “immediately dangerous to life and health” levelset by NIOSH is 50,000 ppm.This study describes an occupational hygiene study in three different meat-processing plants, whichused dry ice to refrigerate packages, and documents how a change in production techniques (i.e., theincreased 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 hospitalizedfor dizziness, hyperventilation, vomiting, and headaches. The interviews also revealed that the amountof dry ice used from one day to another varied greatly. Scheduling the full-day survey so thatrepresentative 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. Carewas taken not to include exhaled air while sampling inside workers’ breathing zones, since exhaledbreath can contain as much as 59,000 ppm carbon dioxide. Normal outdoor air contains about 350–400ppm of carbon dioxide.The short-term detector tubes were used to determine where full-shift samples were needed. The8-h TWA was determined using a bag sampling procedure and gas chromatography (NIOSH AnalyticalMethod 5249). A previous attempt to measure TWA exposures using long-term detector tubes showedthat 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 thelong-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 inthe bag was determined in three ways: (1) short-term detector tubes were used to measure theconcentration of CO 2inside the bag, (2) an aliquot from the bag was transferred to a vacuum samplerand then shipped to the laboratory (this was considered necessary because of the possibility of bagbreakage 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 becauseof 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