PRINCIPLES OF TOXICOLOGY

TABLE 22.5 Comparison of Time-Weighted Average Breathing Zone Samples Using Bag Sampling,
Vacuum-Sampling Cans, and Short-Term Detector Tubes a
TWA Bag
TWA Bag
TWA Bag Concentration Concentration
Concentration Measured Using Vacu- Measured Directly
Measured with Sampler and Gas Using Gas
Detector Tube on Site Chromatography in Chromatography in
Plant Location
(ppm) Laboratory (ppm) Laboratory (ppm)
1 Holding cooler worker 4,900 5,800 3,700
Palletizing line
(outside holding cooler)
4,500 5,200 3,300
Dry ice packaging, worker 1 4,500 6,300 3,500
Dry ice packaging, worker 2 12,700 13,000 800 b
3 Holding cooler worker 5,600 6,400 1,900 b
Dry ice packaging, worker 1 5,900 6,500 500 b
Dry ice packaging, worker 2 9,700 11,500 8,000
Dry ice packaging worker 3 6,800 7,800 4,600
4 Dry ice packaging, worker 1 9,700 10,800 10,300
Dry ice packaging, worker 2 14,000 15,100 12,800
Dry ice packaging, worker 3 20,000 21,800 25,000
Holding cooler, worker 1
(palletizing operation)
9,000 10,400 9,600
Holding cooler, worker 2
(palletizing operation)
14,000 15,300 14,300
a
Sampling times were approximately 300 min.
b
Bags clearly leaked during shipment to laboratory.
22.4 CASE STUDIES 549
CO 2 generated during package charging. Recommendations involving more complete enclosure (i.e.,
a better hood design) and increased exhaust air flow rates were made and found to be feasible.
Local exhaust ventilation systems obviously are not appropriate for controlling exposure levels
inside the holding coolers where concentrations are greatest. Dilution ventilation rates were calculated,
along with the cost of cooling the incoming fresh air. One way of reducing the energy costs involved
the specification of an air-to-air heat exchanger to recover the energy in the cool, contaminated air
about to be exhausted. Alarm systems were also specified for holding coolers to warn of dangerous
atmospheres.
Administrative controls were also found to be effective. Workers involved in the palletizing
operation inside the holding cooler were simply relocated to the outside plant area, where there was
greater dilution. In another plant, workers were rotated in and out of the holding coolers on an hourly
basis. This reduced TWA exposure but increased the chances of a sensitive worker being adversely
affected. Some entry into holding coolers by forklift drivers was still necessary, but the overall
exposures were dramatically reduced, and no further hospitalizations were reported.
Training efforts were also conducted to dispel the myth that dry ice is a harmless substance. Workers
became skilled in recognizing the various signs of carbon dioxide intoxication in both themselves and
in others. Material Safety Data Sheets were made available, and areas which could contain high levels
of carbon dioxide were placarded with warning signs. Workers were trained in how to respond to the
alarm systems which were installed.
Residential Lead-Based Paint Risk Assessment
Industrial hygiene includes evaluation and control of hazards in the community as well as the
workplace. This case study describes how hazards associated with childhood lead poisoning were