Characterization of particle exposure in ferrochromium and stainless steel production

Exposure characterization and risk assessment of ultrafine particles from the blast furnace process in a steelmaking plant

OBJECTIVES

This study aimed to clarify the exposure characteristics and risks of ultrafine particles from the blast furnace process and to provide a reasonable control strategy for protecting the health of workers.

METHODS

The blast furnace location of a steelmaking plant was selected as a typical investigation site. A membrane-based sampling system was used to collect ultrafine particles to analyze their morphology and elemental compositions. A real-time system was used to monitor the total number concentration (NC), total respirable mass concentration (MC), surface area concentration (SAC), and size distribution by number. The risk level of ultrafine particles was analyzed using the Stoffenmanager-Nano model.

RESULTS

The total NC, total MC, and SAC increased significantly relative to background concentrations after slag releasing started and decreased gradually after the activity stopped. The three highest total concentrations during slag releasing were 3-10 times higher than those of the background or non-activity period. The ultrafine particles were mainly gathered at 10.4 or 40 nm, and presented as lump-like agglomerates. The metal elements (Al and Pt) in the ultrafine particles originated from slag and iron ore. The risk level of the ultrafine particles was high, indicating the existing control measures were insufficient.

CONCLUSIONS

The blast furnace workers are at high risk due to exposure to high levels of ultrafine particles associated with working activity and with a bimodal size distribution. The existing control strategies, including engineering control, management control, and personal protection equipment need to be improved.

Exposure to Ultrafine Particles in the Ferroalloy Industry Using a Logbook Method

Background: It is difficult to assess workers’ exposure to ultrafine particles (UFP) due to the lack of personal sampling equipment available for this particle fraction. The logbook method has been proposed as a general method for exposure assessment. This method measures the time and concentration components of the time-weighted average concentration separately and could be suitable for investigation of UFP exposure. Objectives: In this study, we have assessed workers’ exposure to UFP in a ferrosilicon plant. The main tasks of the furnace workers were identified, and the logbook method was used in combination with stationary measurements of UFP taken as close to the identified task areas as possible. In order to verify the results, respirable particles were collected using stationary sampling in close proximity to the UFP measuring instrument, and personal full-shift sampling of respirable particles was performed simultaneously. Thus, exposure to respirable particles determined using the logbook method could be compared to the results of standard measurement. Methods: The particle number concentration of ultrafine particles was determined using a NanoScan SMPS. Respirable particle concentration and exposure were determined using a sampling train consisting of a pump, filter, filter cassettes, and SKC Cyclone for the respirable fraction. Attendance times for workers at each work location were registered via thorough observations made by the research team. Results: The logbook method for exposure estimation based on stationary sampling equipment made it possible to calculate UFP exposure for workers operating the furnaces at a ferrosilicon plant. The mid-size furnace and the large furnace were evaluated separately. The workers operating the largest furnace were exposed to 1.47 × 10⁴ particles/cm³, while workers operating the mid-size furnace were exposed to 2.06 × 10⁴ particles/cm³, with a mean of 1.74 × 10⁴ particles/cm³. Substantial contributions from the casting area, ladle transport corridor, and both tapping areas were made. Exposure to respirable particles was 2.04 mg/m³ (logbook); 2.26 mg/m³ (personal sampling) for workers operating the large-sized furnace, 3.24 mg/m³ (logbook); 2.44 mg/m³ (personal sampling) for workers operating the medium-sized furnace, and 2.57 mg/m³ (logbook); 2.53 mg/m³(personal sampling) on average of all tappers. The average ratio of these two methods’ results was 1.02, which indicates that the logbook method could be used as a substitute for personal sampling when it is not possible to perform personal sampling, at least within this industry. Conclusions: The logbook method is a useful supplement for exposure assessment of UFP, able to identify the most polluted areas of the workplace and the contribution of different work tasks to the total exposure of workers, enabling companies to take action to reduce exposure.