Robert L. Harris

A model for deposition of fibers in the human respiratory system

A mathematical model for estimating lung deposition of fibers is described. It is based on the aerodynamic behavior of thin straight rods. Predicted deposition values for rods of various equivalent aerodynamic diameters and lengths, for each of three tidal volumes and for each of three respiratory system compartments are reported.

Reconstruction of Silica Exposure in the North Carolina Dusty Trades

The current occupational standard for quartz exposure is largely drawn from studies of the granite workers at Barre, Vermont. Since 1935, the North Carolina Dusty Trades program has accumulated data on work-place environmental conditions, occupational history and health status for persons exposed to silica in a broad range of mineral industries, including granite dimension stone. The environmental data have been collected with Greenburg-Smith and midget impingers and the respirable mass dust sampler. A procedure is presented to combine the results of these sampling methods and estimate exposure at the various jobs at each dusty trades plant. From an individuals occupational history, the environmental exposure estimates are used to formulate personal lifetime exposure summaries. The results of this procedure in the North Carolina granite industry compared well with historical data from Vermont granite sheds.

Worker exposures to chemical agents in the manufacture of rubber tires: Solvent vapor studies

Environmental sampling surveys have been conducted in ten large tire manufacturing plants across the U.S. to characterize the nature and intensity of current exposure to solvent vapors. These plants were chosen to represent a cross-section of the industry and include both old and new plants, plants of four different companies and plants with wide geographic distributions. A variety of organic solvents is used in the manufacture of tires and tubes; accordingly solvent vapors comprise one category of exposure for workers in specific Occupational Title Groups (OTGs). Approximately 1000 determinations of various solvent vapor components in air samples have been made with special emphasis on pentane, hexane, heptane, benzene and toluene vapor levels. Exposures stem from the widespread use of bulk materials including petroleum naphthas, gasoline and aliphatic and rubber solvents in various tire manufacturing operations.

Worker exposure to chemical agents in the manufacture of rubber tires and tubes: Particulates

The Occupational Health Studies Group industrial hygiene studies at a group of 14 tire and tube manufacturing plants chosen to represent a cross-section of the industry include numerous evaluations of potential exposure to airborne particulate matter. Results of these environmental particulate sampling studies are reported by plant and by occupational groups within plants. High volume, open face and cyclone samplers were employed to evaluate both personnel and area particulate concentrations. The concentrations of particulates yielded by high volume and open face total particulate samplers are compared with those of comparison samples of respirable material. Personnel samples of particulates are compared with general air samples taken in the same work areas. An overall review and comparison is given of particulate exposures to workers in various occupational title groups where particulate materials are released to the air from processes or operations.

Autocorrelation of Interday Exposures at an Automobile Assembly Plant

This article presents an analysis of interday autocorrelation in the exposure time series of workers in an automobile assembly plant. In all, serial 8-hour time-weighted average exposures for six workers, two each at three separate processes, were monitored for periods ranging from 20 to 110 consecutive days. Autocorrelation was assessed in each case. In general the results support the conclusions of previous investigations, in that relatively little autocorrelation was observed. However, uncertainties regarding the stationarity of the time series over the period of interest highlight potential difficulties in autocorrelation analysis. Particularly, nonrandom events in a plant, such as ventilation and process changes and extended down times, should be considered in any autocorrelation analysis inasmuch as these factors may affect the distributional parameters as well as the stationarity of the time series. In the workplace under study these nonrandom events appear to be more important in the overall asses...

Guideline for Collection of Industrial Hygiene Exposure Assessment Data for Epidemiologic Use

Abstract Workplace exposures of employees are assessed by corporate industrial hygienists for a variety of purposes, most often for compliance with regulations or with consensus or corporate exposure guidelines. With adequate documentation and means for linking results with groups of workers, the results of most exposure assessment efforts may be useful in future epidemiologic studies. As part of its Epidemiology Resource and Information Center (ERIC) program, the Chemical Manufacturers Association supported the development of guidelines for the collection of industrial hygiene exposure assessment data in such a way that they will be useful in future epidemiology studies. Discussions with corporate experts and a review of forms used by several well-developed corporate industrial hygiene programs demonstrated that most of the documentation needed to make exposure assessment information somewhat, if not ideally, useful in epidemiology is currently routinely collected in those programs. The guideline develop...

Effects of Endocrine Disruptors on Dehydroepiandrosterone Sulfotransferase and Enzymes Involved in PAPS Synthesis: Genomic and Nongenomic Pathways

Background Sulfation plays an important role both in detoxification and in the control of steroid activity. Studies in rodents have shown that the conversion of dehydroepiandrosterone (DHEA) to DHEA-sulfate is involved in learning and the memory process. Methods The effects of a range of plasticizers and related compounds commonly encountered in the environment were evaluated kinetically against human DHEA sulfotransferase (SULT 2A1) and by reverse transcriptase-polymerase chain reaction (RT-PCR) against several enzymes involved in the synthesis of the sulfotransferase cofactor adenosine 3′-phosphate 5′-phosphosulfate (PAPS). Results We found that several of the chemicals acted as competitive inhibitors of SULT 2A1 (Ki for 4-tert-octylphenol is 2.8 μM). Additionally, after treatment of TE 671 cells with 0.005–0.5 μM 4-n-octylphenol, bis(2-ethylhexyl)phthalate, and diisodecyl phthalate, real-time RT-PCR showed dose-dependent decreases in the steady-state mRNA levels of cysteine dioxygenase type I, sulfite oxidase, and 3′-phosphate 5′-phosphosulfate synthase I. Conclusions These data suggest that environmental contaminants may exert effects on neuronal function both by direct inhibition of sulfotransferase enzymes and by interrupting the supply of PAPS, which has wider implications for endocrine disruption and xenobiotic metabolism.

Computer Simulation of Radiant Heat Load and Control Alternatives

A digital computer program for calculating the exchange of radiant heat between an absorber and a multiplicity of radiators in its surroundings is described. A matrix of absorber locations within a workspace having radiators in its surroundings may be specified, permitting the construction of isopleths of heat load in the workspace for any elevation of interest. The contribution of each individual radiator to the heat load on the absorber is obtained. Repeated computer runs with simple changes in input data may be used to simulate various control alternatives. The program permits mathematical assessment of radiant heat exchange problems for which manual calculations would be prohibitively tune-consuming and costly.

Design of Dilution Ventilation for Sensible and Latent Heat

Abstract The design of dilution ventilation for control of heat stress requires consideration of both sensible and latent heat. Heat balance equations are used to develop a design procedure which takes into account both forms of heat. By use of the WBGT index in the American Conference of Governmental Industrial Hygienists Threshold Limit Value (TLV) for heat stress, a limiting exposure value for the natural wet bulb temperature in a workplace can be determined. The psychrometric chart constant enthalpy line for moist air associated with this limiting natural wet bulb temperature, along with psychrometric conditions of available dilution air, permits calculation of the amount of dilution ventilation required to satisfy the TLV. For design of dilution ventilation for plants or processes not yet in operation, values for the amounts of latent and sensible heat to be released to the ventilated space and mixing coefficients may have to be estimated. For existing processes or operations, the measurements of ven...