Metal and Nonmetal Diesel Particulate Matter (DPM) Standard Error Factors for 350 μg/m Total Carbon Exposure Limit

As with all other exposure-based M/NM compliance determinations, MSHA will address uncontrollable sampling and analytical errors (SAE) by allowing a margin of error before issuing a citation for exceeding the total carbon (TC) limit. In addition to using the sum of organic carbon (OC) and elemental carbon (EC) as a measure of total carbon (i.e. TC(OC+EC)) MSHA will employ an enforcement policy for the personal exposure limit that will use elemental carbon as a measure of TC (i.e. TC(ECx1.3)). This policy will assure that a citation based on the 350 microgram per cubic meter of air (μg/m) limit of TC is valid and not the result of interferences. MSHA has developed appropriate error factors to account for variability in sampling and analysis from such things as pump flow rate, filters, and the NIOSH 5040 method. If the TC(OC+EC) measurement is equal to or below 350 (μg/m) times the error factor, MSHA will not issue a citation. If the TC(OC+EC) measurement is above the error factor level of 396 μg/m (350 μg/m times 1.13), MSHA will look at the EC measurement from the sample and apply a factor of 1.3 to produce a statistical estimate of TC without interferences. As a matter of enforcement discretion, MSHA will use the TC(ECx1.3) measurement as a check to validate that an overexposure is not the result of interferences. The Agency will issue a citation only if the personal exposure measurement demonstrates noncompliance with at least 95-percent confidence. We will achieve this 95percent confidence level by comparing each TC and EC measurement to the concentration limit multiplied by the appropriate error factor. The error factor (EF) is calculated as where CV ) 645 . 1 ( 1 total CV EF × + = total is the coefficient of variation of the combined sampling and analytical method. The error factor accounts for three uncontrollable variance components represented by CVtotal and then applied to the eight-hour equivalent full-shift measurement of TC(OC+EC) or TC(ECx1.3) using Method 5040. The three components address: (1) pump performance relative to the nominal airflow of 1.7 L/min, (2) variability of the deposit area