Michael J. Ellenbecker

Analyses of the recycling potential of medical plastic wastes

This study analyzed the recycling potential of plastic wastes generated by health care facilities. For this study, we obtained waste streams and recycling data from five typical city hospitals and medical centers and three animal hospitals in Massachusetts. We analyzed the sources, disposal costs and plastic content of medical wastes, and also determined the components, sources, types and amounts of medical plastic wastes. We then evaluated the recycling potential of plastic wastes produced by general city hospital departments, such as cafeterias, operating rooms, laboratories, emergency rooms, ambulance service and facilities, and animal hospitals. Facilities, laboratories, operating rooms, and cafeterias were identified as major sources of plastic wastes generated by hospitals. It was determined that the recycling potential of plastics generated in hospital cafeterias was much greater than that in other departments. This was mainly due to a very slight chance of contamination or infection and simplification of purchasing plastic components. Finally, we discuss methods to increase the recycling of medical plastic wastes. This study suggests that a classification at waste generating sources, depending upon infection chance and/or plastic component, could be a method for the improved recycling of plastic wastes in hospitals.

Focused actions to protect carbon nanotube workers

There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers.

Particulate emission factors for small wood and coal stoves

Emission factors for particulate matter and carbon monoxide have been measured for wood, anthracite coal, and bituminous coal burned in residential heaters operated at less than 15 kW (50,000 Btu/hr). In these studies the stove effluent is mixed with about four volumes of outside air and samples are collected about two minutes after mixing. The main purpose of using this sampling method is to simulate atmospheric conditions more closely. Particulate samples are collected on 20 × 25 cm filters after cyclone preseparation of particles larger than 4 μm. Carbon monoxide concentrations are measured with Draeger tubes. Particulate emission factors for wood ranged from 1.6 to 6.4 g/kg (fuel) and were found to depend on the fuel load and the firing rate, as indicated by earlier studies. These values are substantially less than the values obtained previously for stoves operated under similar conditions. The average particulate emission factors for bituminous and anthracite coal are 10.4 and 0.50 g/kg, respectively...

Airborne Nanoparticle Exposures while Using Constant-Flow, Constant-Velocity, and Air-Curtain-Isolated Fume Hoods

Tsai et al. (Airborne nanoparticle exposures associated with the manual handling of nanoalumina and nanosilver in fume hoods. J Nanopart Res 2009; 11: 147-61) found that the handling of dry nanoalumina and nanosilver inside laboratory fume hoods can cause a significant release of airborne nanoparticles from the hood. Hood design affects the magnitude of release. With traditionally designed fume hoods, the airflow moves horizontally toward the hood cupboard; the turbulent airflow formed in the worker wake region interacts with the vortex in the constant-flow fume hood and this can cause nanoparticles to be carried out with the circulating airflow. Airborne particle concentrations were measured for three hood designs (constant-flow, constant-velocity, and air-curtain hoods) using manual handling of nanoalumina particles. The hood operators airborne nanoparticle breathing zone exposure was measured over the size range from 5 nm to 20 mum. Experiments showed that the exposure magnitude for a constant-flow hood had high variability. The results for the constant-velocity hood varied by operating conditions, but were usually very low. The performance of the air-curtain hood, a new design with significantly different airflow pattern from traditional hoods, was consistent under all operating conditions and release was barely detected. Fog tests showed more intense turbulent airflow in traditional hoods and that the downward airflow from the double-layered sash to the suction slot of the air-curtain hood did not cause turbulence seen in other hoods.

Engineering controls as an intervention to reduce worker exposure

The implementation of controls to reduce worker exposure should be considered the ultimate goal of any successful industrial hygiene program. The industrial hygiene literature has consistently described a hierarchy of controls, consisting first of the engineering controls (substitution, isolation, ventilation), and followed by administrative controls (personal protective equipment, worker education, scheduling etc.). Recently, exhaust ventilation has been the most popular form of engineering control technology for controlling exposure to airborne contaminants. The use of ventilation to control exposures is not without its problems, however, and many of these problems potentially are more severe in smaller companies. This paper proposes a new emphasis on the first control in the hierarchy, substitution. Historically, substitution has meant the substitution of a hazardous chemical or process by one that is less so. This definition is too restrictive; because of this, it is proposed instead to use the term process change, defined as the use of any process modifications that serve to reduce worker exposure. The advantages and disadvantages of the process change approach are discussed and are illustrated with case studies.

Theory for pressure drop in a pulse-jet cleaned fabric filter

Abstract A theory based on Darcys law has been derived which relates pressure drop in a pulse-jet cleaned fabric filter to characteristics of the filter and dust. Assumptions made are that total pressure drop is the sum of pressure drops across the clean bag and dust deposit, and that the fraction of dust removed from a bag by a cleaning pulse is proportional to the reverse pressure drop across it at cleaning. The theory allows prediction of pressure drop under stable or variable operating conditions including dust concentration, filtration velocity, pulse pressure and pulse frequency, and can be used to identify operating conditions which cause pressure drop to increase without limit. Agreement between the model and experimental data is reasonably good.

Prevention Strategies in Industrial Hygiene: A Critical Literature Review

Little is known of the extent of use of industrial hygiene prevention and control strategies in actual workplaces. The recent occupational safety and health literature was identified as a potential source for identifying which strategies are being utilized and evaluated as a means of controlling or preventing chemical hazards. Using preestablished selection criteria, the peer-reviewed industrial hygiene literature 1994-1999 was searched for articles describing prevention and control strategies for chemical hazards in actual workplaces. Ninety-two articles were found and categorized by the type of strategy discussed, whether strategies were implemented and evaluated, and by several other categories. Almost three-quarters discussed engineering control strategies, mostly local exhaust ventilation. Administrative strategies, including housekeeping, personal hygiene, and medical surveillance, appeared in about half the articles. Personal protective equipment was considered in one-third of the articles, and primary prevention strategies, such as material substitution, were considered in one-quarter. Intervention effectiveness was not consistently evaluated in these articles. In response to these findings, recommendations are made to improve the evaluation and promotion of effective prevention and control strategies.

The effect of dust retention on pressure drop in a high velocity pulse-jet fabric filter

Abstract Pulse-jet fabric filters exhibit abnormally high pressure drops when operated at higher than normal superficial filtration velocities. The causes of high pressure drop are investigated for a pilot scale pulse-jet filter collecting fly ash at 50, 75, 100, 125 and 150 mm/s filtration velocities. The measured equilibrium pressure drops ranged from 0.35 kPa (1.4 in. H2O) at low velocity to 10.2 kPa (40.8 in. H2O) at high velocity. Retention of a large mass of dust on the fabric was found to have a significant effect on equilibrium pressure drop at all the tested filtration velocities. The dust deposits distribution, total mass, and specific resistance (K2) all remained essentially constant at lower filtration velocities, but changed dramatically at the highest test velocity. At the 150 mm/s velocity the total dust mass doubled, the dust distribution equalized over the surface of each bag, and K2 increased by a factor of 4.7.

The potential flow solution for air flow into a flanged circular hood

The empirically derived equation for the centerline velocity gradient of a flanged circular inlet, obtained by DallaValle in the 1930s, is still used today as a basis for local exhaust design. This paper presents a theoretical solution for the three-dimensional velocity field into a flanged circular hood, and compares the results with velocity contours obtained by DallaValle. A simple and easily-used equation is derived for computing the velocity at any point under the influence of the hood.

Empirical Validation of Theoretical Velocity Fields into Flanged Circular Hoods

Previously presented theoretical models of the three-dimensional velocity field into a flanged circular hood, both with and without crossdraft, are examined by hot film anemometry. A final model with empirical modifications is selected and validated. Computer generated streamline maps, which enable visualization of the effects of crossdrafts on hood performance, are presented. The theoretical basis for capture efficiency using the model is discussed.