Submicrometer elemental carbon as a selective measure of diesel particulate matter in coal mines

Abstract

A monitoring method for diesel particulate matter was published as Method 5040 by the National Institute for Occupational Safety and Health (NIOSH). Organic and elemental carbon are determined by the method, but elemental carbon (EC) is a better exposure measure. The US Mine Safety and Health Administration (MSHA) proposed use of NIOSH 5040 for compliance determinations in metal and nonmetal mines. MSHA also published a rulemaking for coal mines, but no exposure standard was provided. A standard based on particulate carbon is not considered practical because of coal dust interference. Interference may not be a problem if an appropriate size-selective sampler and EC exposure standard are employed. Submicrometer dust concentrations found in previous surveys of nondieselized, underground coal mines were relatively low. If a large fraction of the submicrometer dust is organic and mineral matter, submicrometer EC concentrations would be much lower than submicrometer mass concentrations. Laboratory and field results reported herein indicate the amount of EC contributed by submicrometer coal dust is minor. In a laboratory test, a submicrometer EC concentration of 31 µg m⁻³ was found when sampling a respirable coal dust concentration over three times the US compliance limit (2 mg m⁻³). Laboratory results are consistent with surveys of nondieselized coal mines, where EC results ranged from below the method limit of detection to 18 µg m⁻³ when size-selective samplers were used to collect dust fractions having particle diameters below 1.5 µm—submicrometer EC concentrations were ≈7 µg m⁻³. In dieselized mines, submicrometer EC concentrations are much higher.