Evaluating Exhaust Exposures of an Alternative Fuel, Gdiesel®, for Underground Mining

Abstract

Introduction: Diesel fuel (D) is used in a variety of applications for several industries, including transportation, agriculture, railroads, construction, and mining. In addition to being non-renewable, combustion of diesel fuel (D) leads to negative occupational health outcomes in mining. Currently the Mine Safety and Health Administration (MSHA) regulates diesel exhaust exposure with an 8-hour, time-weighted average permissible exposure limit (PEL) of 160 µg/m3 respirable (<1.0 µm in size) diesel particulate matter (rDPM). Alternative fuels such as biodiesel (B) and a natural gas/diesel blend (GDiesel® [G]) are considered promising alternatives. While the former fuel has been extensively investigated, the latter has not. Objectives: The aims of this dissertation were: (1) to evaluate and compare D and G exhaust exposures from operation of a Wagner and a (2) JCI load-haul-dump (LHD) at the University of Arizona San Xavier Underground Mining Laboratory (SX); and (3) to synthesize existing peer-reviewed literature comparing D emission exposures to those of B and/or G. Methods: For Aims 1 and 2, operator-location and area exposure samples were collected for 200 minutes in an underground mining laboratory while an LHD with oxidation catalyst was operated with D and then G fuel. Analytes of interest included total diesel particulate matter (tDPM) and rDPM, total and respirable elemental and organic carbon (tEC, rEC, tOC, rOC, respectively), as well as the carbonyl compound (CC) formaldehyde (CH2O), nitric oxide (NO), and nitrogen dioxide (NO2). Exposure assessment was conducted within the guidelines of the National Institute of Occupational Safety and Health’s (NIOSH) Manual of Analytical Methods. Specifically, methods #5040 (tDPM, tEC, tOC, rDPM, rEC, rOC), #6014 (NO, NO2), and #2016 (CH2O). Reported laboratory results were time-weighted over an 8-hour period. Between-fuel comparisons were performed using Wilcoxon rank sum testing. Results: For Aim 1, twenty-three D and 12 G samples were collected. Use of G in the Wagner LHD showed statistically and practically significant reductions in rDPM, tDPM, elemental and organic carbons, NO, NO2, and CH2O. For Aim 2, twenty D and 16 G samples were collected. Use of G in the JCI LHD was associated with a significant decrease in NO2 (p=0.012), and significant increase in rEC (p=0.024). After removing outliers, tEC also showed significant increase (p=0.023). Most of the 20 scholarly works reviewed utilized a laboratory setting (75%), while just 15% were conducted in the field, and 10% simulated field conditions. Twenty percent (4) of studies specifically focused on the mining industry. In addition, most evaluated soy-based B (56%) but did not utilize pollution controls (70%) on equipment. Generally, literature showed that use of B decreased DPM and increased oxides of nitrogen (NOx) emission exposures. While more studies (5) showed increases in CCs, two showed decreases. Discussion: Our studies show that: 1) the use of G has potential for statistically and practically significant reductions in several D exhaust contaminants regulated by MSHA; and 2) variability in exposure and emission concentrations across engine, pollution control and operation configurations exists for B and likely exists for G. Differences observed across fuels and studies are also likely due to fuel composition and characteristics, and combustion temperatures. Further occupational health research is needed to evaluate G emissions under controlled conditions with various equipment configurations, as well as in-field settings to determine whether G exhaust exposures are reduced and actually less toxic than those of D. The impact of this work is substantial and timely. Recent increases in respiratory disease prevalence among miners, including young miners, concerns occupational health and industrial hygiene professionals. In addition, MSHA has requested information regarding diesel exhaust controls and is considering future revisions to the rDPM standard. Efforts to reduce D exhaust emissions will also impact occupational and environmental health worldwide.