Using Laser Absorption Techniques to Monitor Diesel Particulate 

Matter Exposure in Underground Stone Mines 

James Noll; Sam Janisko 

U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control 

and Prevention, National Institute for Occupational Safety and Health, Pittsburgh Research Lab, 626 

Cochrans Mill Road, Pittsburgh, PA 15236 

ABSTRACT 

Underground miners are exposed to some of the highest levels of diesel particulate matter (DPM) in the United 

States. Therefore, it is important to monitor the exposure ofminers to DPM, but it can be difficult because ofthe 

complex composition ofDPM and the number ofinterferences. Currently, elemental carbon (EC) is used as a surrogate 

because it makes up a significant fraction of the DPM and is not affected by interferences. Standard measurement 

methods for EC can be time consuming and only record end of shift results. In this research, a laser absorption 

technique that enables one to measure EC concentration in near real time was shown to be a beneficial tool. The real 

time data showed that the fresh air being drawn into a stone mine was not properly reaching the working area and needed 

to be redirected to decrease DPM concentrations. The real time data also provided a more accurate efficiency of an 

environmental cab compared to just using the standard method by detecting the opening of the cab's window and door. 

The EC optical monitor was also worn by researchers in a mine to show how it can give not only the average 

concentration for the shift but also reveal when and where a miner is exposed to DPM. 

Keywords: Laser absorption, diesel, elemental carbon, mining, exposure 
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1. INTRODUCTION 

Long-term exposure to elevated concentrations of diesel exhaust is a concern, because diesel particulate matter 

(DPM) is believed to be a possible carcinogen. 1-3 Exposure to elevated concentrations of diesel exhaust has also been 

linked to health effects such as eye and nose irritation, headaches, nausea, and asthma. 4-6 Underground miners are 

exposed to some of the highest levels of diesel exhaust in the United States. Therefore, the Mine Safety and Health 

Administration (MSHA) has promulgated rules to limit the exposure ofmetaVnonmetal underground miners to diesel 

particulate matter (DPM) (personal exposure limit of 438 for the 2007 interim limit and 200 for a final limit 

effective in 2008).7-8 In order to promulgate this rule, one issue that had to be overcome was how to measure for DPM 

DPM is a complex mixture ofparticulate elemental carbon (EC) or soot, particulate and particle bound organic carbon 

(OC), sulfates, some metals, etc.9 In the mining environment, mass measurements ofDPM are prone to interferences 

from other sources of aerosols (mineral dust, cigarette smoke, etc.) and are not sensitive enough for measuring the 

concentrations near the fmallimit (below 200 Therefore, a surrogate was needed to determine DPM exposure. 

Both elemental carbon and total carbon could be potential surrogates since both can be accurately measured at the 

concentrations needed using National Institute for Occupational Safety and Health (NIOSH) method 5040 and are major 

components of DPM At ftrst, total carbon (TC) was considered by MSHA to be the most adequate surrogate for DPM 

because TC accounts for over 80% of the DPM while EC to DPM ratios more drastically vary depending upon load 

on the engine. However, the EC and OC particles from mineral dust and OC aerosols from the other sources commonly 

present in underground mines, such as environmental tobacco smoke and oil mist, were found to interfere with the TC 

analysis. A size selective sampler 11-13 has been shown to effectively segregate the coarse mineral dust from the 

generally submicron DPM. Unfortunately, the size selective samplers are not very efficient at removing cigarette smoke 

and oil mist (OC aerosols that generally belong to the same size category as diesel aerosols). Therefore, cigarette smoke 

and oil mist cannot always be avoided when taking personal samples. In addition to aerosol interferences, when using 

TC as a surrogate, one has to also account for organic carbon vapor sampling artifacts. 14-16 

As a result, MSHA turned to also using EC as well as TC as a surrogate for DPM for the interim limit since no other 

sources of submicron EC are known to exist in the metaVnon-metal mining environment. EC is also a major component 

of DPM, and preliminary data shows a good relationship between DPM and EC in underground mines. 17-18 The interim 

2007 limit is a total carbon standard of350 TC (80 % of the 438 DPM standard). In order to determine if a 

mine is out of compliance, both total carbon and elemental carbon are measured. Total carbon is determined in two 

ways: by the actual NIOSH 5040 measurement and the calculation of TC using the EC measurement (1.3 x EC). Ifthe 

TC from a sample is above 350 using both methods, it is considered out of compliance. The sampling strategy for 

the limit has not yet been decided. 

The standard method for measuring the exposure of DPM in underground mines is to collect the particulate matter in 

the environment by passing air through a quartz at l. 7 lpm for an entire shift and analyze the for elemental 

carbon (EC) and total carbon (TC) by NIOSH Method 5040. 19.

20 To avoid mineral dust which can cause an interference 

to the total carbon measurement, a single-stage impactor having a cut point (diameter of particle collected 50% 13 collection efficacy) of 0.8 @ 1.7 Llmin is used. 11. At times, a dynamic blank is used to compensate for the 

absorption of vapor phase organic carbon. 

Using the NIOSH method 5040, samples have to be sent to a laboratory to be analyzed with results coming back 

weeks later. Also, the mine only receives information on a miner's average DPM exposure for an entire shift. A real 

time method for measuring elemental carbon would give a mine the capability to evaluate where the highest 

concentrations of DPM are in the mine (i.e. where the miner was exposed to the highest concentration). It would also 

give the capability of immediately evaluating the DPM concentration when changing different parameters such as 

ventilation. 

2.2 Standard sampling setup 

In the standard sampling procedure (see Figure 2), the sampling train, consisting of a DPM cassette (SKC, Inc., 

Eighty Four, PA), a Dorr-Oliver cyclone, and an Elf Escort personal pump (Mine Safety Applicances Company, 

Pittsburgh, PA) was used to collect ambient air samples at 1.7 lpm (liters per minute). SKC DPM cassettes incorporate 

an impactor with a 0.8 cutpoint and two quartz fiber filters placed in tandem. The filters were analyzed for OC and 

EC using NIOSH method 5040. This system is designed to be worn by the miner (personal sampling (Figure 2b)) and 

can be used for area sampling. 

a b 

Figure 2: (a) The standard sampling setup which consists of an impactor with two quartz fiber filters inside attached to a 

cyclone in a lapel holder. Tubing connects the lapel holder to the personal pump. (b) The setup is designed to be worn by the miner 

by attaching the lapel holder to the clothing and the pump to the miner's belt. 

2.3 NIOSH analytical method 5040 

This analytical method analyzes for OC and EC in two different stages. In the stage, the OC is measured 

by ramping the oven temperature over four progressively higher temperature steps programmed into the instrument, with 

the last step being at about 870 DC in a pure helium (He) atmosphere. The EC does not evolve because there is no 

oxygen (02) available for it to react. The evolved OC is oxidized to carbon dioxide (C02), reduced to methane 

and finaJJy measured using a flame ionization detector (FID). In the second stage, the EC is measured by reducing the 

oven temperature to about 600 DC and then again raising the temperature to about 900 DC in a He/02 atmosphere (02 is 

now present to react with the EC to form CO2), The EC is then measured in the same way as the Oc. TC is simply the 

sum ofOC and EC. The NIOSH method 5040 also optically corrects for pyrolysis (charring) ofOC. This method is 

explained in more detail elsewhere.23 

2.4 Area Sampling 

Area samples were taken at several locations in a stone mine to determine the DPM concentrations in this mine 

and the effects of the current ventilation system. In a basket on a tripod (see Figure 3), the EC monitor as well as three 

SKC DPM cassettes (standard setup method for EC and TC) were run for six hours of a shift during actual production of 

an underground stone mine. A basket was setup at the intake of the mine (fresh air brought into the mine), the return 

(the exit of the intake air after passing through the whole mine), and at two locations at the working area where loaders 

were scooping the limestone and loading it into haul trucks. There was also drilling, roof bolting, and scaling at the 

working areas. The EC monitors were downloaded each day and the EC concentration was calculated using a 

calibration curve. The quarts filters from the SKC DPM cassettes were analyzed for EC and TC at the NIOSH 

Pittsburgh Research Laboratory using NIOSH 5040. 23 Samples were taken for three days. 
Figure 3: Apparatus for area sampling includes an EC monitor for real time analysis, SKC DPM cassettes for NIOSH 

5040 analysis, and a carbon dioxide monitor. 

2.5 Sampling in Cabs 

In order to minimize the exposure of a miner to DPM, environmental cabs are sometimes used. These cabs are 

air conditioned and filter out the DPM to provide a cleaner atmosphere for the miner. In order to evaluate the efficiency 

of a cab, two baskets containing an EC monitor plus three SKC DPM cassettes were made. The baskets were then 

strapped onto a loader (a Caterpillar 980F) outside the cab. Another identical basket was placed inside the cab of the 

vehicle where the miner works. The loader was used to clean up areas the mine and was run during nonnal 

production for this stone mine. After about 6 hours of sampling, the samples were removed from the vehicle. These 

procedures were continued for five days at a stone mine. 

The quartz filters from the SKC DPM cassettes were analyzed for EC and TC at the NIOSH Pittsburgh 

Research Laboratory using NlOSH 5040. 23 The EC monitors were downloaded each day and the EC concentration was 

calculated using a calibration curve. 

2.6 Personal Sampling 

In order to detennine how well the EC monitor could be worn, two NIOSH researchers wore a standard 

sampling apparatus and an EC monitor as seen in Figure 4. The NIOSH researchers were in the to setup samplers 

for the area sampling mentioned earlier. The researchers first setup samplers at the return, then at the working areas, and 

finally at the intake. The real time data can show what concentrations the researcher was exposed to these areas at the 

time of setup. Since the researchers also wore the standard sampling apparatus, it could also be detennined how the EC 

monitor compares to the standard method when being worn. As the previous studies, the quartz filters from the 

standard method were analyzed for EC using NIOSH 5040. 

Figure 4: EC monitor is designed to be worn by a miner. It fits on the miner's belt with a camp lamp and self rescuer. 





h

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