Diesel Emissions Exposure Measurements in Underground Mines

Contact: Professor Pierre Mousset-Jones (775) 784 6959 mousset@mines.unr.edu

Objectives

• Characterize chemical composition and particle size distributions of organic and inorganic contaminants from specific sources and in ambient air in underground gold mines;
• Apportion the contribution of specific sources (e.g., diesel equipment, mechanical particle generation, oil mist, cigarette smoke, etc.) to the total ambient airborne contaminant load in the mines; Estimate exposures of mine workers to these sources.

Background and Purpose

On October 29, 1998, the U.S. Department of Labor's Mine Safety and Health Administration (MSHA) proposed new rules that establish health standards for underground metal and non-metal (or non-coal) mines that use diesel equipment. The rule establishes a concentration limit that would be phased in over a five-year period. An interim limit of 400 *g/m3 of total carbon will go into effect following an 18-month period of MSHA education and technical assistance to mine operators. A final limit of 160 *g/m3 is become effective in five years. Surveys of some mines showed that the workers' exposures to diesel particulate matter (DPM) significantly exceed (on the order of few hundred percent) proposed health standards. However, the contributions of potential sources to worker exposure are not ce rtain. Reliable methods for measuring human exposure to diesel emissions and attributing source contributions are needed in order to develop effective approaches to attain the new standards.

Methods that are available for sampling and analysis of DPM in metal and nonmetal mines are:

• respirable combustible dust (RCD)
• size selective (SS) sampling
• elemental carbon (EC) analysis

Although each provides information concerning DPM, none measures DPM directly. Thus, a method is needed to evaluate EC analysis as a technique for estimating DPM exposure.

Proposed Approach

• Establish distinct chemical profiles for: a) emissions from diesel equipment used in the mines; b) drilling and lube oil mist; c) particulate matter mechanically generated from raw mining material; and d) other sources of aerosol that may be present i n the mines, including cigarette smoking. These profiles will be based on specific organic compounds (particularly polycyclic aromatic hydrocarbons, hopanes and steranes), trace elements, organic and elemental carbon, particle sizes, and inorganic ions e mitted by each source type.

• Apply the Chemical Mass Balance (CMB) receptor model to apportion aerosols present in mines to their respective sources. Estimate absolute (µg/m3) and relative (percentage) source contributions and examine spatial variations within the mine. Exa mine relationships between source contribution estimates in different areas of the mine to estimates obtained from personal monitoring samples, and place these findings in context with the activity patterns of the workers.

• Compare medium-volume, fixed-site sampling with low-volume portable, personal sampling.

Source Profiles

To establish specific chemical profiles, detailed chemical analyses will be performed for diesel exhaust, drilling and lube oil, mineral/rock dust, and other possible aerosol sources in mines. We propose to utilize particulate and gaseous PAH, nitro-PAH, and other organic compounds (e.g., hopanes and steranes, long chain alkanes, iso- and anteisoalkanes) in combination with inorganic particulate species and total elemental and organic carbon for distinguishing sources of fine particles by CMB modeling. In addition, we propose to use MOUDI samplers (Micro-Orifice Uniform Deposit Impactor), which will provide size-resolved gravimetric and chemical data. A single MOUDI instrument covers the size range from 15 to 0.1 *m (a 0.05 *m stage is also available) in eight stages. To determine the ultrafine particle concentrations, the Scanning Mobility Analyzer (SMA) will be used. The SMA provides a portable method of determining the concentration of ultrafine particles as a function of size between 0.01 and 0.5 *m . The diesel equipment exhaust samples will be collected using DRI's dilution sampler, which simulates the dilution and aging processes of primary emissions in the atmosphere.

The DRI dilution sampler works by drawing emissions in from the stack through the heated sample line to a dilution tunnel of 15 cm diameter. The exhaust is mixed in the tunnel with dilution air under turbulent flow conditions to cool and dilute the exhau st to near ambient conditions. After passing through the tunnel, a fraction of the diluted exhaust is drawn into the large chamber where additional residence time is provided to allow the sample to cool and for condensation to occur.

Ambient Air Characterization

Ambient air samples will be collected on filters followed by PUF/XAD/PUF cartridges and analyzed by GC/MS for PAH, nitro-PAH, hopanes, steranes and other organic compounds. MOUDI samplers will provide size-resolved gravimetric and chemical data. These sa mplers will be installed at selected locations in the mine, such as exhaust and intake airways, near diesel production equipment, etc.

Personal Exposure

Mine workers will be equipped with portable, size-selective samplers, similar to that described by Cantrell and Rubow (1992) and McCartney and Cantrell (1992), to measure exposure to diesel particles and semi-volatile organic compounds (SVOCs) as workers move from one location to another. The sampler shown Figure 5, is capable of isolating the fraction that contains the DPM less than 1 µm from the crustal particulate matter typically found in underground mines. An SVOC sorbent (PUF/XAD) tube i s added to the original sampler design to trap any SVOCs that pass through the filter. In addition, the sample is split downstream of the of the impactor with one side passing through a quartz filter followed by a PUF/XAD/PUF cartridge, and the other sid e passing through a Teflon filter. This design modification enables the same type of analyses as planned for samples taken from the stationary samplers.

The portable personal sampler will be compared to DRI's stationary samplers by collocated sampling. Six miners per 12-hour shift will carry a personal sampler. These miners will be selected at random from among operators of diesel equipment and truck dr ivers. Three control workers will be selected from the mine workforce that will not engage in below-ground activity. At the end of each shift, the air samples will be retrieved, along with a record of where each miner and control personnel worked, the typ e of equipment used, and how long they worked at each location. This activity will be conducted for two shifts for a minimum total of 18 samples.

After visiting several candidate mines, Newmont Gold Mine of Carlin, Nevada was selected based on known particulate levels, extensive use of diesel equipment, and available logistical support.

Expected Benefits

The database developed as a result of this proposed work can be applied in future studies to apportion the diesel contributions to ambient particulate matter. Additional benefits accruing from this work include:

• Chemical characterization and size distribution of heavy-duty diesel particulate matter.
• Size distribution of ambient particulate matter in underground mines.
• Baseline for mine and other underground worker exposure.
• Development of a personal SVOC sampling system to assess individual exposure to diesel particulate matter.
• Comparison of data obtained from personal sampling systems with those obtained from stationary samplers.

References

• Cantrell, B.K., and K.L. Rubow (1992). "Measurement of diesel exhaust aerosol in underground coal mines." In Diesels in Underground Mines: Measurement and Control of Particulate Emissions, Proceedings of the Bureau of Mines Information and Technol ogy Transfer Seminar, Minneapolis, MN, September 29-30, pp 11-17.

• McCartney, T.C., and B.K. Cantrell (1992). "A cost-effective personal diesel exhaust aerosol sampler." In Diesels in Underground Mines: Measurement and Control of Particulate Emissions, Proceedings of the Bureau of Mines Information and Technology Transfer Seminar, Minneapolis, MN, September 29-30, pp 24-30.