Dental distress. A possible relief.

The exacting task of endodontics can be considerably complicated by the behaviour of patients who have heightened fears and reactions to the manipulations involved. Hypnotherapy may offer a way to reduce these fears and enhance the comfort of both patient and dentist.

Mist concentration measurements. II: Laboratory and field evaluations.

Sampling methods to determine occupational exposures to metalworking fluid mists are subject to bias. Light-scattering devices may respond differently to variations in particle size, shape, and refractive index. Gravimetric samplers are prone to evaporative losses of semi-volatile components. The performance of two light scattering devices, an electrostatic precipitator, and filters followed by gravimetric analysis was investigated when measuring metalworking fluid mist in laboratory and field settings. Laboratory tests with soluble oil and field tests with soluble oil, straight oil, and semi-synthetic fluid showed significant evaporative losses from filters. Light-scattering devices tended to overestimate mist concentrations when mass median diameters were less than about 2 microns and to underestimate mist concentrations when mass median diameters were larger. Filters will underestimate occupational exposures to metalworking fluid mists when semi-volatile components are present.

Performance of industrial mist collectors over time.

Effective, economical control of metalworking fluid mists at the source is important, because exposure to these mists may cause adverse health effects. This study investigated performance changes over time for industrial collectors that removed metalworking fluid mist in the laboratory and in a transmission plant. Aerosizers were used to measure the efficiency of each stage in several multistage collectors as a function of mist droplet diameter, for up to one year of continuous operation. Metal-mesh, first-stage filters operated at low pressure drops and were effective at removing droplets larger than 3 to 5 microns in diameter. Some second-stage filters worked better than others. Both "65 percent" and "95 percent" cartridge filters failed after only a few weeks; their efficiencies decreased substantially over that time. Pocket filters and cylindrical cartridges used as second-stage filters also decreased in efficiency for submicron droplets. Whereas filters for solid particles load continuously to form a dust cake that increases efficiency, mist filters form no cake and load only to the point where collection equals drainage. As a mist filter loads, the interstitial gas velocity increases, so that efficiency decreases for small droplets that collect by diffusion. Although a third-stage 95 percent DOP filter showed important decreases in efficiency over time for submicron droplets, third-stage HEPA filters operated with efficiencies that consistently approaches 100 percent for droplets of all sizes, even after one year of operation. These results suggest that the performance of second-stage filters can be improved if they can be made to drain collected liquid more effectively. For high efficiency, mist collectors should use a HEPA filter as a final stage.

Laboratory measurements of oil mist concentrations using filters and an electrostatic precipitator.

This study investigated the potential for mineral oil mist to evaporate, during sampling, from filters and electrostatic precipitator substrates used to assess personal exposure. If sample evaporation occurs, reported mist concentrations will underestimate true exposure. Mineral oil used as a machining fluid is not normally considered volatile; however, when dispersed as mist its aggregate surface area is so high that significant evaporation can occur. National Institute for Occupational Safety and Health Method 5026 specifies that oil mist concentrations should be determined by collecting mist on filters of mixed cellulose esters (MCE) or polyvinyl chloride (PVC). Collected mist droplets remain dispersed on the filter surface and in contact with passing air while sampling continues, conditions that can lead to sample evaporation. Less evaporation should occur for samples taken with an electrostatic precipitator, where mist droplets are separated from the airflow by electrostatic force and coalesce on the precipitator wall to form a film with relatively low surface area. Collection of mineral oil mist was investigated using a precipitator designed for personal sampling and using either an MCE or a PVC filter. The amounts of oil mist collected using the precipitator were significantly higher than the amounts collected using the filters, p < 0.001. Further tests in which clean air passed through mist-loaded precipitators and filters showed that the precipitator retained substantially more collected mist than both filters, p < 0.001, and further suggested that the MCE filter retained more mist than the PVC filter, p = 0.059. Differences in sample collection and retention between the precipitator and the filters were particularly pronounced at mist loadings below 1 mg.

Experimental examination of factors that affect dust generation.

A method is presented to examine factors that affect the amount and size distribution of dust generated by falling granular material in still air. This work was conducted by using an apparatus with separate dust generating and dust measuring sections. The dust generated by a falling material was carried into an elutriation column equipped with a slotted Sierra high-volume impactor at the top. This apparatus can measure dust generation rates for particles between 0.4 and 25 microns in aerodynamic diameter as well as the amount of air entrained by the falling material. Four granular materials were tested, and a simple model was developed to describe the dust generation rate of these materials as a function of particle size, drop height, material flow, and moisture content. Moisture content strongly influenced the interparticle binding forces and the amount of dust generated. Drop height and material flow influenced the material separation forces and also significantly influenced the amount of dust generated.

Evaluation of respiratory effects in miners and millers exposed to talc free of asbestos and silica.

Miners and millers of talc ore, free from asbestos and silica, were examined for respiratory effects. A study of 116 subjects included the modified British Medical Research Council respiratory symptom questionnaire, simple spirometry, chest radiography, and limited examination of the chest. A one-year follow-up evaluation was performed on 103 subjects. Of the 12 subjects whose chest radiographs showed small round or irregular opacities (perfusion 1/0 or greater), five had never smoked cigarettes. Pulmonary function values at the time of the initial study were less than predicted and the rates of loss of FEV1 and FVC greater than expected. These differences were in part attributed to cigarette smoking but were greater than predicted from that source alone. There was evidence of an exposure effect after adjusting for cigarette smoking and we conclude that these workers have been affected by their exposures. No clear interaction between smoking and exposure could be identified. Populations such as this will need to be studied for longer periods to determine what current dust levels are safe.