<![CDATA[Coal remains a major fossil fuel in the industrial and power-generation sectors, which makes rigorous quality assessment essential to determining its suitability for use. Prior studies on sub-bituminous coal quality have typically reported mean values of proximate and sulfur parameters without testing statistically which parameter drives quality differences among samples. This study evaluated 20 coal samples from a mining area in Kutai Barat Regency, East Kalimantan, Indonesia, through proximate analysis, total sulfur determination, and calorific value measurement under ASTM standards (D3173-17a, D3174-12, D3175-20, D4239, and D5865), coupled with normality testing and one-way ANOVA to assess the statistical significance of variation among coal sub-ranks. Mean values were 13.44% moisture, 15.24% ash, 40.21% volatile matter, 40.89% fixed carbon, 0.379% total sulfur, and 5,517.20 kcal/kg calorific value; all six parameters followed a normal distribution (p 0.05, Kolmogorov-Smirnov and Shapiro-Wilk). One-way ANOVA across the three sub-rank groups (Sub-bituminous A, B, and C) showed that moisture, volatile matter, fixed carbon, total sulfur, and calorific value did not differ significantly (p 0.05), whereas ash content did (p 0.033; F 4.194), identifying ash content as the single dominant driver of sub-rank variation within this mining area. Under ASTM D388, every sample fell within the Sub-bituminous rank (30% Class A, 60% Class B, 10% Class C), with low sulfur content (1%) favorable for environmental performance, although combustion efficiency is constrained by a comparatively high ash content. These findings support pairing ASTM-standard laboratory testing with variance-based statistical evaluation to map quality drivers at the scale of mine operations.]]>
