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An extensive literature review revealed few published reports on the wet cleaning and reusing industrial HEPA filters, except for those on metallic and glass fiber filters. Accordingly, the effects of particulate loading on pressure drop and the capture efficiency of new custom-fabricated high-efficiency particulate air (HEPA) filters were determined in this research and the findings were compared with those of the same filters after being wet cleaned and reused multiple times. A set of five samples from three different types of HEPA rated filtration media, made of polypropylene (Puritrate®), Teflon and glass fiber filters, were fabricated in the cylindrical shape. Each filter was mounted in a specially designed filter-testing unit and gradually loaded with airborne particles of cadmium telluride (CdTe) in 10-gram increments up to a total of 100 grams. During the loading, the face velocity of each filter was kept constant at 17. 8 m/s (3500 ft/min). Four filters (two Puritrate® and two Teflon) were fully loaded 4-10 times. Each time, they were wet cleaned in dilute (< 4%) nitric acid-soaked for 24 hours, rinsed with deionized water, and gradually dried at ambient temperature under a laboratory hood until the filter gained its original weight. The glass fiber was used as a reference medium; it was loaded and tested only once and was not wet-cleaned or reused. The pressure drop across all filters (new or reused) increased by cubic model expression as the filters were gradually loaded. Baseline pressure drop on the new (unused) filters ranged from 45 Pa (Puritrate®) to 115 Pa (Teflon). As the filter loading progressed, the pressure drop ranged from 146 Pa (Puritrate®) to 306 Pa (Teflon). After each wet-cleaning and drying cycle, the filters' pressure drop returned almost to their original baselines. All filters, new or reused, performed well, with particulate capture efficiencies exceeding 99.97% at 0.3 µm. The results suggested that certain custom fabricated HEPA filters can effectively be wet-cleaned and reused. [ABSTRACT FROM AUTHOR]

Respirators are commonly used to protect workers against workplace airborne contaminants, but this equipment may become a safety hazard by creating discomfort, disorientation and postural instability. Although postural stability is critical to workers, especially those working near moving objects or on surfaces where a loss of balance may become life threatening, little attention has been given to the effect of respirators on wearers' postural stability. The purpose of this study was to examine the effects of wearing a half-mask respirator, a full-face respirator, a self-contained breathing apparatus (SCBA), and no-respirator on postural stability, using computerized dynamic posturography (CDP). The subjects' perception of comfort was also assessed. Over 60% of the subjects reported that wearing a respirator was uncomfortable and 20% felt that they had difficulty balancing while wearing the SCBA. The half-mask respirators, full-face respirators or SCBA did not produce any differences in postural stability over a baseline (no-respirator). However, the subjects expressed concerns with comfort. [ABSTRACT FROM AUTHOR]

Objective: To determine the changes in respiratory function within one hour and three hours of exposure to formaldehyde and investigate the relation between exposure to formaldehyde and acute changes in respiratory function. Method: Respiratory function of 50 nonsmoking medical students exposed to formaldehyde in a gross anatomy laboratory were compared with respiratory function of 36 non-exposed, non-smoking physiotherapy students. Formaldehyde concentrations were measured in the breathing zone of each exposed subject and in the general work environment. Results: Formaldehyde concentrations in the breathing zoneof exposed subjects generally exceeded recommended standards. On average, the variables of respiratory function of both the exposed and the control subjects increased significantly within one hour and from one to three hours after exposure. The increase in respiratory function of the exposed subjects was significantly less than that of the control subjects. There was no meaningful correlation between concentration of formaldehyde in the breathing zone and changes in the respiratory function of exposed subjects. Conclusion: As the increase in therespiratory function of the subjects can be attributable to normal diurnal variation, the significantly lower increase in respiratory function of the exposed group than in the control group is probably due to exposure to formaldehyde. The results of this study do not, however, support a dose-response relation. [ABSTRACT FROM AUTHOR]

Storage of radon-producing material in two silos and two waste pits is one of the major environmental and occupational issues at a formeruranium production facility, now a Superfund site. In addition, up to 100 metric tons of thorium is stored on the northeast side of the site. Concentrations of radium up to 17,600 Bq g-1 (477,000pCi g-1) or higher for silos and up to 45 Bq g-1 (1,200 pCi g-1) for waste pits have been reported. Thisstudy was conducted to identify factors and climatic conditions thatcontribute to higher radon levels and to assess workers' exposure atthe site. Data covering a 12-mo period were compiled from monitoringhourly real-time radon levels at indoor (within 3 buildings) and outdoor (at 14 on-site and 2 off-site monitoring stations) locations andfrom hourly site-specific meteorological information. The ranges of radon levels were as follows: 1.8-3,655 Bq m-3 (0.05-98.8 pCi L-1) outdoor on-site, 3.7-329 Bq m-3 (0.1-8.9 pCi L-1) outdoor off-site, and 1.8-111 Bq m-3 (0.05-3.0 pCi L-1) indoor on-site. Only radon levels in the vicinity of the storage silos were significantly higher than levels off-site. Radon concentrations showed diurnal variations, with maximum levels occurring in the early morning and minimum levels in the afternoon. Seasonal variation was also observed, with radon levels higher during the summer through early fall and lower during the late winter through spring. Wind speed, relative humidity, and wind direction appeared to be the most significant predictors of radon concentration. The estimated radon dose to workers, calculated by using exposure models and annual average levels of radon in the work area, was below recommended exposure limits. These results suggest that the emission control methods at this site have been effective in maintaining environmental radon contamination and workers' exposure at acceptable levels. [ABSTRACT FROM AUTHOR]