Respirable crystalline silica exposures during asphalt pavement milling at eleven highway construction sites.

Asphalt pavement milling machines use a rotating cutter drum to remove the deteriorated road surface for recycling. The removal of the road surface has the potential to release respirable crystalline silica, to which workers can be exposed. This article describes an evaluation of respirable crystalline silica exposures to the operator and ground worker from two different half-lane and larger asphalt pavement milling machines that had ventilation dust controls and water-sprays designed and installed by the manufacturers. Manufacturer A completed milling for 11 days at 4 highway construction sites in Wisconsin, and Manufacturer B completed milling for 10 days at 7 highway construction sites in Indiana. To evaluate the dust controls, full-shift personal breathing zone air samples were collected from an operator and ground worker during the course of normal employee work activities of asphalt pavement milling at 11 different sites. Forty-two personal breathing zone air samples were collected over 21 days (sampling on an operator and ground worker each day). All samples were below 50 µg/m(3) for respirable crystalline silica, the National Institute for Occupational Safety and Health recommended exposure limit. The geometric mean personal breathing zone air sample was 6.2 µg/m(3) for the operator and 6.1 µg/m(3) for the ground worker for the Manufacturer A milling machine. The geometric mean personal breathing zone air sample was 4.2 µg/m(3) for the operator and 9.0 µg/m(3) for the ground worker for the Manufacturer B milling machine. In addition, upper 95% confidence limits for the mean exposure for each occupation were well below 50 µg/m(3) for both studies. The silica content in the bulk asphalt material being milled ranged from 7-23% silica for roads milled by Manufacturer A and from 5-12% silica for roads milled by Manufacturer B. The results indicate that engineering controls consisting of ventilation controls in combination with water-sprays are capable of controlling occupational exposures to respirable crystalline silica generated by asphalt pavement milling machines on highway construction sites.

Evaluation of engineering controls for the mixing of flavorings containing diacetyl and other volatile ingredients.

Exposures to diacetyl, a primary ingredient of butter flavoring, have been shown to cause respiratory disease among workers who mix flavorings. This study focused on evaluating ventilation controls designed to reduce emissions from the flavor mixing tanks, the major source of diacetyl in the plants. Five exhaust hood configurations were evaluated in the laboratory: standard hinged lid-opened, standard hinged lid-closed, hinged lid-slotted, dome with 38-mm gap, and dome with 114-mm gap. Tracer gas tests were performed to evaluate quantitative capture efficiency for each hood. A perforated copper coil was used to simulate an area source within the 1.2-meter diameter mixing tank. Capture efficiencies were measured at four hood exhaust flow rates (2.83, 5.66, 11.3, and 17.0 cubic meters per min) and three cross draft velocities (0, 30, and 60 meters per min). All hoods evaluated performed well with capture efficiencies above 90% for most combinations of exhaust volume and cross drafts. The standard hinged lid was the least expensive to manufacture and had the best average capture efficiency (over 99%) in the closed configuration for all exhaust flow rates and cross drafts. The hinged lid-slotted hood had some of the lowest capture efficiencies at the low exhaust flow rates compared to the other hood designs. The standard hinged lid performed well, even in the open position, and it provided a flexible approach to controlling emissions from mixing tanks. The dome hood gave results comparable to the standard hinged lid but it is more expensive to manufacture. The results of the study indicate that emissions from mixing tanks used in the production of flavorings can be controlled using simple inexpensive exhaust hoods.

Interlaboratory evaluation of trace element determination in workplace air filter samples by inductively coupled plasma mass spectrometry.

Inductively coupled plasma mass spectrometry (ICP-MS) is becoming more widely used for trace elemental analysis in the occupational hygiene field, and consequently new ICP-MS international standard procedures have been promulgated by ASTM International and ISO. However, there is a dearth of interlaboratory performance data for this analytical methodology. In an effort to fill this data void, an interlaboratory evaluation of ICP-MS for determining trace elements in workplace air samples was conducted, towards fulfillment of method validation requirements for international voluntary consensus standard test methods. The study was performed in accordance with applicable statistical procedures for investigating interlaboratory precision. The evaluation was carried out using certified 37-mm diameter mixed-cellulose ester (MCE) filters that were fortified with 21 elements of concern in occupational hygiene. Elements were spiked at levels ranging from 0.025 to 10 µg filter(-1), with three different filter loadings denoted "Low", "Medium" and "High". Participating laboratories were recruited from a pool of over fifty invitees; ultimately twenty laboratories from Europe, North America and Asia submitted results. Triplicates of each certified filter with elemental contents at three different levels, plus media blanks spiked with reagent, were conveyed to each volunteer laboratory. Each participant was also provided a copy of the test method which each participant was asked to follow; spiking levels were unknown to the participants. The laboratories were requested to prepare the filters by one of three sample preparation procedures, i.e., hotplate digestion, microwave digestion or hot block extraction, which were described in the test method. Participants were then asked to analyze aliquots of the prepared samples by ICP-MS, and to report their data in units of µg filter(-1). Most interlaboratory precision estimates were acceptable for medium- and high-level spikes (RSD <25%), but generally yielded greater uncertainties than were anticipated at the outset of the study.

Status of worker exposure to asphalt paving fumes with the use of engineering controls.

Since 1996, industry, labor, and government have partnered to minimize workers' exposure to asphalt fumes using engineering controls. The objective of this study was to determine the use after some years of experience and to benchmark the effectiveness of the engineering controls as compared to the current exposure limits. To accomplish this objective, the current highway class pavers equipped with controls to reduce asphalt fumes, occupational exposure levels, and ventilation flow rates were monitored, and a user acceptance survey was conducted. Personal breathing-zone sampling was administered to determine concentrations of total particulate matter (TPM) and benzene soluble matter (BSM). Personal monitoring of workers yielded a BSM arithmetic mean of 0.13 mg/m3 (95% confidence limits (0.07, 0.43) mg/m3). All site average worker BSM values are below the American Conference of Governmental Industrial Hygienists (ACGIH) adopted threshold limit value (TLV) time weighted average (TWA) of 0.5 mg/m3 as benzene soluble inhalable particulate, although five sites contained 95% confidence limits slightly above the ACGIH TLV. The TPM arithmetic mean was 0.35 mg/m3 (95% confidence limits (0.27, 0.69) mg/m3). All sites showed average worker and area TPM values below NIOSH's recommended exposure limit for asphalt fumes (5 mg/m3, 15 min). One screed area sample and one operator area sample were also taken each day. Area samples followed a similar pattern to the worker breathing zone samples, but were generally slightly higher in TPM and BSM concentration. The effect of work practices and application temperatures appears to have an impact on the ability of the engineering controls to keep exposure below the TLV for BSM. To gain a better understanding of the aerodynamic properties of asphalt fumes, particle size and airborne concentrations were also monitored using a TSI model 3320 aerodynamic particle sizer spectrometer. The geometric mean particle size was between 0.64 and 0.98 micrometers for the worker breathing zone samples, with a geometric mean of 0.73 micrometers for all sites. Total airborne concentrations were typically higher for the asphalt fume exposed groups than for the background samples. During high fume events, four 15-minute samples were taken each day. Only one 15-minute sample was above the limit of quantification. Stack flow rates were measured, and results are discussed and compared to the manufacturers' nominal values. Survey results were generally positive, with recommendations discussed for continuous improvement.

Control of wake-induced exposure using an interrupted oscillating jet.

A problem may arise in ventilation design when the contaminant source is located in the worker's wake, where turbulence and vortex formation can carry the contaminant into the breathing zone even though the source is downwind. It was found previously that forced directional variations in the flow can reduce or eliminate the vortex formation that causes these local reversals. Reported here is a simple realization of this concept, in which an oscillating jet of air was directed at a mannequin in an otherwise steady flow of air. A 50th percentile male mannequin was placed in a nearly uniform flow of approximately 0.18 m/sec (36 ft/min). A low-velocity tracer gas source (isobutylene) was held in the standing mannequin's hands with the upper arms vertical and the elbows at 90 degrees. Four ventilation scenarios were compared by concentration measurements in the breathing zone, using photoionization detectors: (A) uniform flow; (B) addition of a steady jet with initial velocity 5.1 m/sec (1.0 x 10(3) ft/min) directed at the mannequin's back, parallel to the main flow; (C) making the jet oscillate to 45 degrees on either side of the centerline with a period of 13 sec; and (D) introducing a blockage at the centerline so the oscillating jet never blew directly at the worker. At the 97.5% confidence level the interrupted oscillating jet (case D) achieved at least 99% exposure reduction compared with the uniform flow by itself (case A), at least 93% compared with the steady jet (case B), and at least 45% exposure reduction compared with the unblocked oscillating jet (case C).

Engineering controls for furniture strippers to meet the OSHA methylene chloride PEL.

This case study demonstrates how methylene chloride exposures during furniture stripping can be reduced to below the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 25 ppm (as an 8-hour time-weighted average). Five surveys were conducted at one facility; the first four resulted in employee exposure geometric means from 39 to 332 ppm. For the fifth survey local exhaust ventilation was used at the stripping tank and the rinsing area, which together exhausted 138 m3/min (4860 ft3/min). Additional controls included providing adequate make-up air, adding paraffin wax to the stripping solution, raising the level of the stripping solution in the tank, and discussing good work practices with the employee. The employees' methylene chloride exposures during the fifth survey resulted in a geometric mean of 5.6 ppm with a 95% upper confidence limit of 8.3 ppm, which was found to be significantly lower than the OSHA PEL and the OSHA action level of 12.5 ppm. The cost of the ventilation system was $8900.

The impact of maintenance and design for ventilation systems.

Ventilation systems need to be designed to include access for cleaning and preventive maintenance. Without such access, the exhaust volume will deteriorate. Because of access difficulties and the many demands on their time, plant managers are sometimes errant in performing proper preventive maintenance. Three surveys measuring workers' exposures to methylene chloride were conducted at the same furniture stripping facility. A new ventilation system was installed for the first survey, resulting in an exhaust volume of 2900 cfm and worker exposure to methylene chloride of 59 ppm (geometric mean). Immediately after the first survey, the gasoline-powered fan was replaced by a smaller capacity electrically powered fan. Deterioration in the ventilation system was seen after seven years. Problems included clogged slots, paint chips and sawdust deposits in plenums, and a loose and frayed fan belt. The second survey indicated a reduction in exhaust volume to 1060 cfm and increased worker exposure to 330 ppm. With the smaller capacity fan still in place, the system was otherwise upgraded to allow for easier access and maintenance was performed. The third survey showed that the ventilation system performance was better (exhaust volume improved to 2080 cfm) and the worker exposures were reduced to 73 ppm. This study shows the benefits of designing for preventive maintenance and the necessity of keeping the ventilation systems clean.

A method for estimation of bias and variability of continuous gas monitor data: application to carbon monoxide monitor accuracy.

A method is presented for the evaluation of the bias, variability, and accuracy of gas monitors. This method is based on using the parameters for the fitted response curves of the monitors. Thereby, variability between calibrations, between dates within each calibration period, and between different units can be evaluated at several different standard concentrations. By combining variability information with bias information, accuracy can be assessed. An example using carbon monoxide monitor data is provided. Although the most general statistical software required for these tasks is not available on a spreadsheet, when the same number of dates in a calibration period are evaluated for each monitor unit, the calculations can be done on a spreadsheet. An example of such calculations, together with the formulas needed for their implementation, is provided. In addition, the methods can be extended by use of appropriate statistical models and software to evaluate monitor trends within calibration periods, as well as consider the effects of other variables, such as humidity and temperature, on monitor variability and bias.