Comparing MCAQD dust control limits to MSHA limits.                       Home Rule 316 declares the limits placed on dust emissions from Twin Knolls mine. Rule 316 relies almost completely on opacity to measure dust. It measures particulates per cubic foot in only 3 sections in Rule 316: 303.2 storage silos, 302.1 production of asphaltic concrete, and 301.1 crushing and screening stack outlet. We use the 301.1 limit. The stack emissions limit is 7% opacity or 0.014 grains per cubic foot. No specific limit for % quartz in the dust, just total particulates. (Rule 316 page 316.14) MSHA does not use opacity so we will use MCAQD's grains per cubic foot (gr/ft3) limit. To make this comparison we have to convert grains to milligrams, cubic feet to cubic meters, then calculate the MCAQD limit in milligrams per cubic meter. We will then have a number to compare to MSHA standards, after we calculate the MSHA particulate limit for dust with this % quartz. Convert grains to milligrams: 1gr = 64.8 mg Convert cubic feet to cubic meters: 1ft3 = 0.028317 m3 Calculate how many ft3 in 1m3: 1 / 0.028317 = 35.31 ft3 Rule 316 limit, in grains, converted to mg: 0.014 * 64.8 = 0.907 mg Rule 316 limit is 0.907 mg/ft3 Convert to mg/m3: 0.907 * 35.31 = 32.03 mg/m3 total particulates The MCAQD allowed emission of dust from Twin Knolls is 32.03 mg/m3 total particulates. MSHA places the upper limit of exposure to respirable quartz at 0.1 mg/m3. To achieve that limit, MSHA permissible exposure limit to dust containing quartz is calculated by using the % quartz in the dust and dividing 10 mg/m3 by (quartz%+2)   MORE INFO We need to note here that MSHA calculations are made using the tested quartz content of the dust but these tests have not yet been done, at least as far as we know. However, using the quartz content of the rock itself should be very close to the same values as in the dust. The low number for quartz content of Twin Knolls granite is 30%. Calculating the limit for 30% quartz in Twin Knolls dust, 10 / 32 = 0.31 mg/m3 total particulates The MSHA upper limit for dust containing 30% quartz is 0.31 mg/m3 total particulates. MCAQD's limit is over 103 times higher. The high number for quartz content of Twin Knolls granite is 70%. Calculating the limit for 70% quartz in Twin Knolls dust, 10 / 72 = 0.1389 mg/m3 total particulates The MSHA upper limit for dust containing 70% quartz is 0.14 mg/m3 total particulates. MCAQD's limit is over 228 times higher! Even if we assume a very unrealistic quartz content of only 1%, 10 / 3 = 3.33 mg/m3 total particulates, the MCAQD limit is still almost 10 times higher.