ASTM D388-23

Standard Classification of Coals by Rank

ABSTRACT
This specification covers the classification of coals by rank, that is, according to their degree of metamorphism, or progressive alteration, in the natural series from lignite to anthracite. These coals are mainly composed of vitrinite. The classification shall be based on gradational properties that depend on the degree of metamorphism. The classification shall also be according to fixed carbon and gross calorific value calculated to the mineral-matter-free basis.
SIGNIFICANCE AND USE
4.1 This classification establishes categories of coal based on gradational properties that depend principally on the degree of metamorphism to which the coal was subjected while buried. These categories indicate ranges of physical and chemical characteristics that are useful in making broad estimates of the behavior of coal in mining, preparation, and use.
SCOPE
1.1 This standard covers the classification of coals by rank, that is, according to their degree of metamorphism, or progressive alteration, in the natural series from lignite to anthracite.  
1.2 This classification is applicable to coals that are composed mainly of vitrinite.  
Note 1: Coals rich in inertinite or liptinite (exinite), or both, cannot be properly classified because, in those macerals, the properties that determine rank (calorific value, volatile matter, and agglomerating character) differ greatly from those of vitrinite in the same coal. Often, such coals can be recognized by megascopic examination. In North America, these coals are mostly nonbanded varieties that contain only a small proportion of vitrain and consist mainly of attrital materials. The degree of metamorphism of nonbanded and other vitrinite-poor coals can be estimated by determining the classification properties of isolated or concentrated vitrinite fractions, or by determining the reflectance of the vitrinite (see Test Method D2798 and Appendix X1 of this classification). However, in the use of these vitrinite-poor coals, some properties normally associated with rank, such as rheology, combustibility, hardness, and grindability (as well as the rank determining properties) may differ substantially from those of vitrinite-rich coals of the same degree of metamorphism.  
1.3 The accuracy of the classification of impure coal may be impaired by the effect of large amounts of mineral matter on the determination of volatile matter and calorific value, and on their calculation to the mineral-matter-free basis.  
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.  
1.4.1 Exception—The values stated in British thermal units per pound (Btu/lb) are to be regarded as the standard. The SI equivalents of Btu/lb are provided for information only and are not considered standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-May-2023
• ICS: 75.160.10 - Solid fuels
• Technical Committee: D05 - Coal and Coke
• Drafting Committee: D05.23 - Sampling

Relations

• Refers: ASTM D121-15(2024) - Standard Terminology of Coal and Coke
• Effective Date: 01-Mar-2024
• Refers: ASTM D720/D720M-23 - Standard Test Method for Free-Swelling Index of Coal
• Effective Date: 01-Nov-2023
• Refers: ASTM D3175-20 - Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke
• Effective Date: 01-Feb-2020
• Refers: ASTM D2234/D2234M-19 - Standard Practice for Collection of a Gross Sample of Coal
• Effective Date: 01-Dec-2019
• Refers: ASTM D2798-11a(2019) - Standard Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal
• Effective Date: 01-Nov-2019
• Refers: ASTM D1412/D1412M-19 - Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
• Effective Date: 01-Jun-2019
• Refers: ASTM D3175-18 - Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke
• Effective Date: 01-Dec-2018
• Refers: ASTM D1412/D1412M-18 - Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
• Effective Date: 01-Nov-2018
• Refers: ASTM D4239-18 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 01-Sep-2018
• Refers: ASTM D2234/D2234M-17 - Standard Practice for Collection of a Gross Sample of Coal
• Effective Date: 15-Oct-2017
• Refers: ASTM D1412/D1412M-17a - Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
• Effective Date: 01-Aug-2017
• Refers: ASTM D1412/D1412M-17 - Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
• Effective Date: 01-Jun-2017
• Refers: ASTM D4239-17 - Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
• Effective Date: 15-May-2017
• Refers: ASTM D3173/D3173M-17 - Standard Test Method for Moisture in the Analysis Sample of Coal and Coke
• Effective Date: 01-Feb-2017
• Refers: ASTM D3175-17 - Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke
• Effective Date: 01-Feb-2017

Overview

ASTM D388-23: Standard Classification of Coals by Rank is an internationally recognized standard developed by ASTM International for the classification and ranking of coals based on their degree of metamorphism-from lignite (low rank) to anthracite (high rank). This classification system is essential for industries relying on coal as it provides a uniform method of assessing coal properties primarily through fixed carbon content and gross calorific value, both calculated on a mineral-matter-free basis. The standard is applicable to coals mainly composed of vitrinite, making it an indispensable reference for coal quality assessment, mining, energy production, and coal utilization sectors.

Key Topics

• Coal Rank Determination: The standard classifies coals by analyzing their degree of metamorphism, reflecting the progressive alteration coal undergoes naturally. The major ranks are lignite, subbituminous, bituminous, and anthracitic.
• Classification Criteria: Rank determination primarily uses:
  • Fixed carbon (FC) content on a dry, mineral-matter-free basis for higher-rank coals.
  • Gross calorific value (GCV) on a moist, mineral-matter-free basis for lower-rank coals.
  • Agglomerating character is also considered for certain coal groups.
• Analytical Methods: The document references standardized test methods for measuring parameters like moisture, ash, sulfur content, and calorific value, ensuring data reliability.
• Application Scope: The standard is most suitable for coals rich in vitrinite. Coals containing significant inertinite or liptinite cannot be accurately ranked using this system.
• Basis of Calculation: Fixed carbon and calorific value are adjusted using equations that factor out mineral matter, ensuring results reflect the actual carbonaceous material in the coal.

Applications

The ASTM D388-23 standard has wide practical value in various sectors that rely on coal classification:

• Mining: Facilitates planning, mining strategies, and valuation by providing a clear classification system.
• Coal Sampling and Preparation: Guides the uniform collection, handling, and analysis of samples for consistent classification results.
• Energy Generation: Power plants and energy providers use coal rank to select appropriate fuels based on calorific value, combustion characteristics, and efficiency.
• Industrial Processes: Industries such as metallurgy and cement require specific coal types for processes like coke production and clinker formation.
• Coal Trade and Marketing: Buyers and sellers use the ranking to communicate and negotiate coal quality, ensuring transparent transactions.
• Environmental Assessment: Understanding coal rank aids in predicting emissions, by-products, and compliance with regulatory standards.

Related Standards

Several ASTM standards are referenced and related to coal analysis and classification:

• ASTM D121: Terminology of Coal and Coke
• ASTM D720/D720M: Free-Swelling Index of Coal
• ASTM D2013/D2013M: Preparing Coal Samples for Analysis
• ASTM D2798: Determination of Vitrinite Reflectance of Coal
• ASTM D3172, D3173/D3173M, D3174, D3175: Proximate Analysis and Determination of Moisture, Ash, and Volatile Matter
• ASTM D3302/D3302M: Total Moisture in Coal
• ASTM D5865: Gross Calorific Value of Coal and Coke

Utilizing ASTM D388-23 in conjunction with these related standards ensures comprehensive, accurate, and internationally recognized coal classification suitable for technical, commercial, and regulatory needs.

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Keywords: ASTM D388, coal classification, coal rank, fixed carbon, gross calorific value, lignite, subbituminous, bituminous, anthracite, vitrinite, coal sampling, coal analysis, ASTM standards, energy generation, mining.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D388 − 23
Standard Classification of
Coals by Rank
This standard is issued under the fixed designation D388; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This standard covers the classification of coals by rank,
mendations issued by the World Trade Organization Technical
that is, according to their degree of metamorphism, or progres-
Barriers to Trade (TBT) Committee.
sive alteration, in the natural series from lignite to anthracite.
1.2 This classification is applicable to coals that are com-
2. Referenced Documents
posed mainly of vitrinite.
2.1 ASTM Standards:
NOTE 1—Coals rich in inertinite or liptinite (exinite), or both, cannot be D121 Terminology of Coal and Coke
properly classified because, in those macerals, the properties that deter-
D720/D720M Test Method for Free-Swelling Index of Coal
mine rank (calorific value, volatile matter, and agglomerating character)
D1412/D1412M Test Method for Equilibrium Moisture of
differ greatly from those of vitrinite in the same coal. Often, such coals can
Coal at 96 to 97 Percent Relative Humidity and 30 °C
be recognized by megascopic examination. In North America, these coals
D2013/D2013M Practice for Preparing Coal Samples for
are mostly nonbanded varieties that contain only a small proportion of
vitrain and consist mainly of attrital materials. The degree of metamor- Analysis
phism of nonbanded and other vitrinite-poor coals can be estimated by
D2234/D2234M Practice for Collection of a Gross Sample
determining the classification properties of isolated or concentrated
of Coal
vitrinite fractions, or by determining the reflectance of the vitrinite (see
D2798 Test Method for Microscopical Determination of the
Test Method D2798 and Appendix X1 of this classification). However, in
Vitrinite Reflectance of Coal
the use of these vitrinite-poor coals, some properties normally associated
with rank, such as rheology, combustibility, hardness, and grindability (as
D3172 Practice for Proximate Analysis of Coal and Coke
well as the rank determining properties) may differ substantially from
D3173/D3173M Test Method for Moisture in the Analysis
those of vitrinite-rich coals of the same degree of metamorphism.
Sample of Coal and Coke
1.3 The accuracy of the classification of impure coal may be
D3174 Test Method for Ash in the Analysis Sample of Coal
impaired by the effect of large amounts of mineral matter on
and Coke from Coal
the determination of volatile matter and calorific value, and on
D3175 Test Method for Volatile Matter in the Analysis
their calculation to the mineral-matter-free basis.
Sample of Coal and Coke
D3302/D3302M Test Method for Total Moisture in Coal
1.4 The values stated in SI units are to be regarded as
D4239 Test Method for Sulfur in the Analysis Sample of
standard. The values given in parentheses are for information
Coal and Coke Using High-Temperature Tube Furnace
only.
Combustion
1.4.1 Exception—The values stated in British thermal units
D4596 Practice for Collection of Channel Samples of Coal
per pound (Btu/lb) are to be regarded as the standard. The SI
in a Mine
equivalents of Btu/lb are provided for information only and are
D5016 Test Method for Total Sulfur in Coal and Coke
not considered standard.
Combustion Residues Using a High-Temperature Tube
1.5 This standard does not purport to address all of the
Furnace Combustion Method with Infrared Absorption
safety concerns, if any, associated with its use. It is the
D5192 Practice for Collection of Coal Samples from Core
responsibility of the user of this standard to establish appro-
D5865 Test Method for Gross Calorific Value of Coal and
priate safety, health, and environmental practices and deter-
Coke
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions:
This classification is under the jurisdiction of ASTM Committee D05 on Coal
and Coke and is the direct responsibility of Subcommittee D05.23 on Sampling. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 15, 2023. Published June 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1934. Last previous edition approved in 2019 as D388 – 19a. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D0388-23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D388 − 23
3.1.1 For additional definitions of terms used in this 3.1.6 group, n—a subdivision within a coal rank class
classification, refer to Terminology D121. indicating a coal’s designated rank; for example, subbitumi-
3.1.2 agglomerating, adj—as applied to coal, the property
nous A rank coal is a group within the subbituminous class.
of softening when heated to above about 400 °C in a nonoxi-
3.1.7 high rank coal, n—denotes a range of coal classes with
dizing atmosphere and appearing as a coherent mass when
a greater degree of metamorphism or alteration, including
cooled to room temperature.
bituminous and anthracitic coals.
3.1.3 apparent rank, n—of a coal seam, the estimated rank
3.1.7.1 Discussion—These coals are generally characterized
designation obtained using samples other than face channel
by lower inherent moisture and higher calorific value. Rank
samples or core samples with 100 % recovery of the seam, but
alone is not a sufficient indicator of whether a coal is suitable
otherwise conforming to procedures of Classification D388.
for a specific end use.
3.1.4 class, n—a designation of coal rank indicating the
3.1.8 low rank coal, n—denotes a range of coal classes with
degree of metamorphism, or progressive alteration.
3.1.4.1 Discussion—In order of increasing metamorphism, a lesser degree of metamorphism or alteration, including
these classes range from lignitic through subbituminous and
lignitic and subbituminous coals.
bituminous to anthracitic coals. Refer to Table 1 of Classifica-
3.1.8.1 Discussion—These coals are generally characterized
tion D388.
by higher inherent moisture and lower calorific value. Rank
3.1.5 coal seam, n—the stratum, layer, or bed of coal
alone is not a sufficient indicator of whether a coal is suitable
(containing less than a 50 % mass fraction of ash on the dry
for a specific end use.
basis) that lies between two other rock layers whose compo-
3.2 Abbreviations:
sitions differ significantly from that of coal.
A
TABLE 1 Classification of Coals by Rank
B
GCV Limits
im,MMf
FC Limits, % VM Limits, %
d,MMf d,MMf
C
Btu/lb MJ/kg
Agglomerating
Class/Group
Equal or Equal or Equal or
Character
Less Greater Equal or
Greater Greater Less Than Greater Less Than
Than Than Less Than
Than Than Than
Anthracitic:
Meta-anthracite 98 . . . . . . 2 . . . . . . . . . . . .
Anthracite 92 98 2 8 . . . . . . . . . . . . non-
agglomerating
J
D
Semianthracite 86 92 8 14 . . . . . . . . . . . .
Bituminous:
Low volatile bituminous coal 78 86 14 22 . . . . . . . . . . . .
Medium volatile bituminous 69 78 22 31 . . . . . . . . . . . .
coal
commonly
High volatile A bituminous . . . 69 31 . . . 14 000 . . . 32.557 . . .
E
agglomerating
coal
High volatile B bituminous . . . . . . . . . . . . 13 000 14 000 30.232 32.557 6
coal
High volatile C bituminous . . . . . . . . . . . . 11 500 13 000 26.743 30.232
coal
H
10 500 11 500 24.418 26.743 agglomerating
Subbituminous:
Subbituminous A coal . . . . . . . . . . . . 10 500 11 500 24.418 26.743
Subbituminous B coal . . . . . . . . . . . . 9 500 10 500 22.09 24.418
Subbituminous C coal . . . . . . . . . . . . 8 300 9 500 19.30 22.09
non-
agglomerating
Lignitic:
Lignite A . . . . . . . . . . . . 6 300 8 300 14.65 19.30 6
Lignite B . . . . . . . . . . . . . . . 6 300 . . . 14.65
A
This classification does not apply to certain coals, as discussed in Section 1.
B
Refers to coal containing its natural inherent moisture but not including visible water on the surface of the coal.
C
Megajoules per kilogram. To convert British thermal units per pound to megajoules per kilogram, multiply by 0.0023255.
D
If agglomerating, classify in low volatile group of the bituminous class.
E
It is recognized that there may be nonagglomerating varieties in these groups of the bituminous class, and that there are notable exceptions in the high volatile C
bituminous group.
D388 − 23
3.2.1 Where it is desired to abbreviate the designation of the %
ranks of coal, the following abbreviations shall be used: VM —volatile matter, inherent moisture basis, %
im
ma—meta-anthracite
an—anthracite 4. Significance and Use
sa—semianthracite
4.1 This classification establishes categories of coal based
lvb—low volatile bituminous
mvb—medium volatile bituminous
on gradational properties that depend principally on the degree
hvAb—high volatile A bituminous
of metamorphism to which the coal was subjected while
hvBb—high volatile B bituminous
buried. These categories indicate ranges of physical and
hvCb—high volatile C bituminous
subA—subbituminous A
chemical characteristics that are useful in making broad
subB—subbituminous B
estimates of the behavior of coal in mining, preparation, and
subC—subbituminous C
use.
ligA—lignite A
ligB—lignite B
5. Basis of Classification
3.3 Symbols:
3.3.1 Descriptive Symbols (symbols used for describing
5.1 Classification is according to fixed carbon and gross
quantities, all in lowercase, roman)
calorific value (expressed in British thermal units per pound,
d—dry basis
Btu/lb) calculated to the mineral-matter-free basis. The higher-
f—free basis (for example, mineral-matter-free and sulfur- rank coals are classified according to fixed carbon on the dry
trioxide-free)
basis; the lower-rank coals are classified according to gross
im—inherent moisture basis calorific value on the moist basis. Agglomerating character is
used to differentiate between certain adjacent groups.
3.3.2 Simple Quantity Symbols (calculated quantities with
units, all in upper case, italicized)
6. Classification by Rank
A—ash, %
FC—fixed carbon, %
6.1 Fixed Carbon and Gross Calorific Value—Coals shall be
FSI—free swelling index
classified by rank in accordance with Table 1.
GCV—gross calorific value, Btu/lb
6.1.1 Coals having 69 % or more fixed carbon on the dry,
IM—inherent moisture, %
mineral-matter-free basis shall be classified according to fixed
MM—mineral matter, %
carbon, regardless of gross calorific value.
S—total sulfur, %
6.1.2 Coals having less than 69 % fixed carbon on the dry,
SO :A—sulfur trioxide in the ash, %
mineral-matter-free basis shall be classified according to gross
SO :C—sulfur trioxide in the ash, expressed as a percentage of
3 calorific value on the moist, mineral-matter-free basis.
the coal, %
6.2 Agglomerating Character—Classify coals having 86 %
VM—volatile matter, %
or more fixed carbon on the dry, mineral-matter-free basis, if
3.3.3 Complex Quantity Symbols (simple quantity symbols
agglomerating, in the low volatile group of the bituminous
with roman subscripts)
class. Classify coals having gross calorific values in the range
A —ash, dry basis (possibly sulfate-bearing), %
d
from 10 500 Btu/lb to 11 500 Btu/lb on the inherent-moisture,
A —ash, inherent-moisture basis, %
im
mineral-matter-free basis according to their agglomerating
A —ash, inherent-moisture basis, sulfur-trioxide-free
im,SO f
3 character (Table 1).
basis, %
6.3 Supplemental Information—A correlation of the ranking
FC —fixed carbon, dry basis, %
d
property, volatile matter (100–fixed carbon), with the mean-
FC —fixed carbon, dry basis, mineral-matter-free basis, %
d,MMf
maximum reflectance of the vitrinite group macerals in coals
FC —fixed carbon, inherent-moisture basis, %
im
tested in one laboratory over a period of several years is shown
FC —fixed carbon, inherent-moisture basis, sulfur-
im,SO f
in Appendix X1.
trioxide-free basis, %
GCV —gross calorific value, dry basis, Btu/lb
d
7. Sampling
GCV —gross calorific value, inherent-moisture basis, Btu/lb
im
GCV —gross calorific value, inherent-moisture basis, 7.1 Samples—Classify a coal seam, or part of a coal seam,
im,MMf
mineral-matter-free basis, Btu/lb in any locality based on the average analysis and gross calorific
MM —mineral matter, dry basis, sulfur-trioxide-free basis, value (and agglomerating character where required) of not less
d,SO f
% than three and preferably five or more whole seam samples,
MM —mineral matter, inherent-moisture basis, sulfur- either face channels or cores, taken in different and uniformly
im,SO f
trioxide-free basis, % distributed localities, either within the same mine or closely
S —total sulfur, dry basis, % adjacent mines representing a continuous and compact area not
d
S —total sulfur, inherent-moisture basis, % greater than approximately 10 km (4 square miles) in regions
im
SO : A —sulfur trioxide in the ash, dry basis, % of geological uniformity. In regions in which conditions
3 d
SO :C —sulfur trioxide in the ash, expressed as a percentage indicate that the coal probably varies rapidly in short distances,
3 im
of the coal, inherent moisture basis, % the spacing of sampling points and grouping of analyses to
VM —volatile matter, dry basis, % provide average values shall not be such that coals of obviously
d
VM —volatile matter, dry basis, mineral-matter-free basis, different rank will be used in calculating average values.
d,MMf
D388 − 23
7.1.1 Take channel samples by excluding mineral partings moisture or somewhat less than that amount. In Appendix X1
more than 1 cm ( ⁄8 in.) and lenses or concretions (such as of Test Method D1412/D1412M, the section titled Character-
sulfur balls) more than 1.25 cm ( ⁄2 in.) thick and 5 cm (2 in.) istics and Conditions of Sampling Locality describes a simple
wide, as specified in Practice D4596. field test that can help determine which case is at hand.
7.1.2 A drill core sample may be used provided it was
NOTE 2—ASTM Manual 11 provides additional useful information
collected as specified in Practice D5192 and meets the follow-
regarding the sampling and handling of core samples.
ing provisions: core recovery is 100 % of the seam, the major
7.2 Other Types of Samples—A standard rank determination
mineral partings and concretions are excluded as specified in
cannot be made unless samples have been obtained in accor-
7.1.1, and drilling mud is removed from the core (see also
dance with 7.1. However, the relation to standard determina-
7.1.6).
tions may be usefully given for other types of samples taken
7.1.3 Place all samples in metal or plastic cans with airtight
under unspecified conditions, providing the same standards of
lids, or heavy vapor impervious bags, properly sealed to
analysis and computation are followed. Designate these com-
preserve inherent moisture.
parative indications as apparent rank, which indicates the
7.1.4 Analyses of samples from outcrops or from weathered
correct relative position for the sample analyzed but does not
or oxidized coal shall not be used for classification by rank.
imply any standards of sampling. Whenever apparent rank is
7.1.5 In case the coal is likely to be classified on the moist
stated, give additional information as to the nature of the
basis, that is, inclusive of its natural complement of inherent
sample.
moisture, take samples in a manner most likely to preserve
7.2.1 The apparent rank of the coal product from a mine
inherent moisture for purposes of analysis. Because some of
shall be based on representative samples taken in accordance
the moisture in a freshly collected sample condenses on the
with the Organization and Planning of Sampling Operations
inside of the sample container, weigh both the container and
section (Section 7) of Practice D2234/D2234M.
the coal before and after air drying, and report the total loss in
7.2.2 In case the coal is likely to be classed on the moist
mass as air-drying loss.
basis, take samples at the tipple or preparation plant and seal
7.1.6 It is often difficult to obtain samples without including
the sample to prevent loss of moisture.
visible surface moisture, such as in typical coring situations
where injected water or drilling mud is used or when the coal
8. Methods of Analysis and Testing
seam is an aquifer. When the as-received basis moisture in
samples is questionable in terms of representing inherent
8.1 Laboratory Sampling and Analysis—Prepare coal in
moisture, and the coal is likely to be classified on the moist
accordance with Practice D2013/D2013M and analyze it in
basis, the sampler shall include the following statement in the
accordance with Test Methods D3173/D3173M, D3174,
description: Moisture questionable. Samples so marked shall
D3175, D4239, D3302/D3302M, and Practice D3172. Deter-
not be used for classification on a moist basis unless brought to
mine its gross calorific value in accordance with Test Method
a standard condition of moisture equilibrium as specified in
D5865. Determine the sulfur trioxide (SO ) retained in the ash
Test Method D1412/D1412M. Analyses of such samples that
in accordance with Test Method D5016 and express the result
have been treated in this manner shall be designated as samples
on a dry basis. Inherent moisture is reported as as-received
equilibrated per Test Method D1412/D1412M.
(AR) moisture if the sample was collected according to 7.1.1 or
7.1.7 Equilibrium moisture results for suspected lignite and
as equilibrium moisture if 7.1.6 (Test Method D1412/D1412M)
subbituminous coals shall be adjusted utilizing the procedure
applies.
outlined in Test Method D1412/D1412M, Appendix X1 to
8.2 Adjust the ash value determined in accordance with Test
estimate inherent moisture c
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D388 − 19a D388 − 23
Standard Classification of
Coals by Rank
This standard is issued under the fixed designation D388; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This standard covers the classification of coals by rank, that is, according to their degree of metamorphism, or progressive
alteration, in the natural series from lignite to anthracite.
1.2 This classification is applicable to coals that are composed mainly of vitrinite.
NOTE 1—Coals rich in inertinite or liptinite (exinite), or both, cannot be properly classified because, in those macerals, the properties that determine rank
(calorific value, volatile matter, and agglomerating character) differ greatly from those of vitrinite in the same coal. Often, such coals can be recognized
by megascopic examination. In North America, these coals are mostly nonbanded varieties that contain only a small proportion of vitrain and consist
mainly of attrital materials. The degree of metamorphism of nonbanded and other vitrinite-poor coals can be estimated by determining the classification
properties of isolated or concentrated vitrinite fractions, or by determining the reflectance of the vitrinite (see Test Method D2798 and Appendix X1 of
this classification). However, in the use of these vitrinite-poor coals, some properties normally associated with rank, such as rheology, combustibility,
hardness, and grindability (as well as the rank determining properties) may differ substantially from those of vitrinite-rich coals of the same degree of
metamorphism.
1.3 The accuracy of the classification of impure coal may be impaired by the effect of large amounts of mineral matter on the
determination of volatile matter and calorific value, and on their calculation to the mineral-matter-free basis.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.4.1 Exception—The values stated in British thermal units per pound (Btu/lb) are to be regarded as the standard. The SI
equivalents of Btu/lb are provided for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D121 Terminology of Coal and Coke
D720/D720M Test Method for Free-Swelling Index of Coal
This classification is under the jurisdiction of ASTM Committee D05 on Coal and Coke and is the direct responsibility of Subcommittee D05.23 on Sampling.
Current edition approved Nov. 1, 2019May 15, 2023. Published November 2019June 2023. Originally approved in 1934. Last previous edition approved in 2019 as
D388 – 19.D388 – 19a. DOI: 10.1520/D0388-19A.10.1520/D0388-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D388 − 23
D1412/D1412M Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30 °C
D2013/D2013M Practice for Preparing Coal Samples for Analysis
D2234/D2234M Practice for Collection of a Gross Sample of Coal
D2798 Test Method for Microscopical Determination of the Vitrinite Reflectance of Coal
D3172 Practice for Proximate Analysis of Coal and Coke
D3173/D3173M Test Method for Moisture in the Analysis Sample of Coal and Coke
D3174 Test Method for Ash in the Analysis Sample of Coal and Coke from Coal
D3175 Test Method for Volatile Matter in the Analysis Sample of Coal and Coke
D3302/D3302M Test Method for Total Moisture in Coal
D4239 Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion
D4596 Practice for Collection of Channel Samples of Coal in a Mine
D5016 Test Method for Total Sulfur in Coal and Coke Combustion Residues Using a High-Temperature Tube Furnace
Combustion Method with Infrared Absorption
D5192 Practice for Collection of Coal Samples from Core
D5865 Test Method for Gross Calorific Value of Coal and Coke
3. Terminology
3.1 Definitions:
3.1.1 For additional definitions of terms used in this classification, refer to Terminology D121.
3.1.2 agglomerating, adj—as applied to coal, the property of softening when heated to above about 400 °C in a nonoxidizing
atmosphere and appearing as a coherent mass when cooled to room temperature.
3.1.3 apparent rank, n—of a coal seam, the estimated rank designation obtained using samples other than face channel samples
or core samples with 100 % recovery of the seam, but otherwise conforming to procedures of Classification D388.
3.1.4 class, n—a designation of coal rank indicating the degree of metamorphism, or progressive alteration.
3.1.4.1 Discussion—
In order of increasing metamorphism, these classes range from lignitic through subbituminous and bituminous to anthracitic coals.
Refer to Table 1 of Classification D388.
3.1.5 coal seam, n—the stratum, layer, or bed of coal (containing less than a 50 % mass fraction of ash on the dry basis) that lies
between two other rock layers whose compositions differ significantly from that of coal.
3.1.6 group, n—a subdivision within a coal rank class indicating a coal’s designated rank; for example, subbituminous A rank coal
is a group within the subbituminous class.
3.1.7 high rank coal, n—denotes a range of coal classes with a greater degree of metamorphism or alteration, including bituminous
and anthracitic coals.
3.1.7.1 Discussion—
These coals are generally characterized by lower inherent moisture and higher calorific value. Rank alone is not a sufficient
indicator of whether a coal is suitable for a specific end use.
3.1.8 low rank coal, n—denotes a range of coal classes with a lesser degree of metamorphism or alteration, including lignitic and
subbituminous coals.
3.1.8.1 Discussion—
These coals are generally characterized by higher inherent moisture and lower calorific value. Rank alone is not a sufficient
indicator of whether a coal is suitable for a specific end use.
3.2 Abbreviations:
D388 − 23
A
TABLE 1 Classification of Coals by Rank
B
GCV Limits
im,MMf
FC Limits, % VM Limits, %
d,MMf d,MMf
C
Btu/lb MJ/kg
Agglomerating
Class/Group
Equal or Equal or Equal or
Character
Less Greater Equal or
Greater Greater Less Than Greater Less Than
Than Than Less Than
Than Than Than
Anthracitic:
Meta-anthracite 98 . . . . . . 2 . . . . . . . . . . . .
Anthracite 92 98 2 8 . . . . . . . . . . . . non-
agglomerating
J
D
Semianthracite 86 92 8 14 . . . . . . . . . . . .
Bituminous:
Low volatile bituminous coal 78 86 14 22 . . . . . . . . . . . .
Medium volatile bituminous 69 78 22 31 . . . . . . . . . . . .
coal
commonly
High volatile A bituminous . . . 69 31 . . . 14 000 . . . 32.557 . . .
E
agglomerating
coal
High volatile B bituminous . . . . . . . . . . . . 13 000 14 000 30.232 32.557
coal
High volatile C bituminous . . . . . . . . . . . . 11 500 13 000 26.743 30.232
coal
H
10 500 11 500 24.418 26.743 agglomerating
Subbituminous:
Subbituminous A coal . . . . . . . . . . . . 10 500 11 500 24.418 26.743
Subbituminous B coal . . . . . . . . . . . . 9 500 10 500 22.09 24.418
Subbituminous C coal . . . . . . . . . . . . 8 300 9 500 19.30 22.09
non-
agglomerating
Lignitic:
Lignite A . . . . . . . . . . . . 6 300 8 300 14.65 19.30 6
Lignite B . . . . . . . . . . . . . . . 6 300 . . . 14.65
A
This classification does not apply to certain coals, as discussed in Section 1.
B
Refers to coal containing its natural inherent moisture but not including visible water on the surface of the coal.
C
Megajoules per kilogram. To convert British thermal units per pound to megajoules per kilogram, multiply by 0.0023255.
D
If agglomerating, classify in low volatile group of the bituminous class.
E
It is recognized that there may be nonagglomerating varieties in these groups of the bituminous class, and that there are notable exceptions in the high volatile C
bituminous group.
3.2.1 Where it is desired to abbreviate the designation of the ranks of coal, the following abbreviations shall be used:
ma—meta-anthracite
an—anthracite
sa—semianthracite
lvb—low volatile bituminous
mvb—medium volatile bituminous
hvAb—high volatile A bituminous
hvBb—high volatile B bituminous
hvCb—high volatile C bituminous
subA—subbituminous A
subB—subbituminous B
subC—subbituminous C
ligA—lignite A
ligB—lignite B
3.3 Symbols:
3.3.1 Descriptive Symbols (symbols used for describing quantities, all in lowercase, roman)
d—dry basis
f—free basis (for example, mineral-matter-free and sulfur-trioxide-free)
im—inherent moisture basis
3.3.2 Simple Quantity Symbols (calculated quantities with units, all in upper case, italicized)
A—ash, %
FC—fixed carbon, %
FSI—free swelling index
D388 − 23
GCV—gross calorific value, Btu/lb
IM—inherent moisture, %
MM—mineral matter, %
S—total sulfur, %
SO :A—sulfur trioxide in the ash, %
SO :C—sulfur trioxide in the ash, expressed as a percentage of the coal, %
VM—volatile matter, %
3.3.3 Complex Quantity Symbols (simple quantity symbols with roman subscripts)
A —ash, dry basis (possibly sulfate-bearing), %
d
A —ash, inherent-moisture basis, %
im
A —ash, inherent-moisture basis, sulfur-trioxide-free basis, %
im,SO f
FC —fixed carbon, dry basis, %
d
FC —fixed carbon, dry basis, mineral-matter-free basis, %
d,MMf
FC —fixed carbon, inherent-moisture basis, %
im
FC —fixed carbon, inherent-moisture basis, sulfur-trioxide-free basis, %
im,SO f
GCV —gross calorific value, dry basis, Btu/lb
d
GCV —gross calorific value, inherent-moisture basis, Btu/lb
im
GCV —gross calorific value, inherent-moisture basis, mineral-matter-free basis, Btu/lb
im,MMf
MM —mineral matter, dry basis, sulfur-trioxide-free basis, %
d,SO f
MM —mineral matter, inherent-moisture basis, sulfur-trioxide-free basis, %
im,SO f
S —total sulfur, dry basis, %
d
S —total sulfur, inherent-moisture basis, %
im
SO : A —sulfur trioxide in the ash, dry basis, %
3 d
SO :C —sulfur trioxide in the ash, expressed as a percentage of the coal, inherent moisture basis, %
3 im
VM —volatile matter, dry basis, %
d
VM —volatile matter, dry basis, mineral-matter-free basis, %
d,MMf
VM —volatile matter, inherent moisture basis, %
im
4. Significance and Use
4.1 This classification establishes categories of coal based on gradational properties that depend principally on the degree of
metamorphism to which the coal was subjected while buried. These categories indicate ranges of physical and chemical
characteristics that are useful in making broad estimates of the behavior of coal in mining, preparation, and use.
5. Basis of Classification
5.1 Classification is according to fixed carbon and gross calorific value (expressed in British thermal units per pound, Btu/lb)
calculated to the mineral-matter-free basis. The higher-rank coals are classified according to fixed carbon on the dry basis; the
lower-rank coals are classified according to gross calorific value on the moist basis. Agglomerating character is used to differentiate
between certain adjacent groups.
6. Classification by Rank
6.1 Fixed Carbon and Gross Calorific Value—Coals shall be classified by rank in accordance with Table 1.
6.1.1 Coals having 69 % or more fixed carbon on the dry, mineral-matter-free basis shall be classified according to fixed carbon,
regardless of gross calorific value.
6.1.2 Coals having less than 69 % fixed carbon on the dry, mineral-matter-free basis shall be classified according to gross calorific
value on the moist, mineral-matter-free basis.
6.2 Agglomerating Character—Classify coals having 86 % or more fixed carbon on the dry, mineral-matter-free basis, if
agglomerating, in the low volatile group of the bituminous class. Classify coals having gross calorific values in the range from
10 500 Btu/lb to 11 500 Btu/lb on the inherent-moisture, mineral-matter-free basis according to their agglomerating character
(Table 1).
D388 − 23
6.3 Supplemental Information—A correlation of the ranking property, volatile matter (100–fixed carbon), with the mean-maximum
reflectance of the vitrinite group macerals in coals tested in one laboratory over a period of several years is shown in Appendix
X1.
7. Sampling
7.1 Samples—Classify a coal seam, or part of a coal seam, in any locality based on the average analysis and gross calorific value
(and agglomerating character where required) of not less than three and preferably five or more whole seam samples, either face
channels or cores, taken in different and uniformly distributed localities, either within the same mine or closely adjacent mines
representing a continuous and compact area not greater than approximately 10 km (4 square miles) in regions of geological
uniformity. In regions in which conditions indicate that the coal probably varies rapidly in short distances, the spacing of sampling
points and grouping of analyses to provide average values shall not be such that coals of obviously different rank will be used in
calculating average values.
7.1.1 Take channel samples by excluding mineral partings more than 1 cm ( ⁄8 in.) and lenses or concretions (such as sulfur balls)
more than 1.25 cm ( ⁄2 in.) thick and 5 cm (2 in.) wide, as specified in Practice D4596.
7.1.2 A drill core sample may be used provided it was collected as specified in Practice D5192 and meets the following provisions:
core recovery is 100 % of the seam, the major mineral partings and concretions are excluded as specified in 7.1.1, and drilling mud
is removed from the core (see also 7.1.6).
7.1.3 Place all samples in metal or plastic cans with airtight lids, or heavy vapor impervious bags, properly sealed to preserve
inherent moisture.
7.1.4 Analyses of samples from outcrops or from weathered or oxidized coal shall not be used for classification by rank.
7.1.5 In case the coal is likely to be classified on the moist basis, that is, inclusive of its natural complement of inherent moisture,
take samples in a manner most likely to preserve inherent moisture for purposes of analysis. Because some of the moisture in a
freshly collected sample condenses on the inside of the sample container, weigh both the container and the coal before and after
air drying, and report the total loss in mass as air-drying loss.
7.1.6 It is often difficult to obtain samples without including visible surface moisture, such as in typical coring situations where
injected water or drilling mud is used or when the coal seam is an aquifer. When the as-received basis moisture in samples is
questionable in terms of representing inherent moisture, and the coal is likely to be classified on the moist basis, the sampler shall
include the following statement in the description: Moisture questionable. Samples so marked shall not be used for classification
on a moist basis unless brought to a standard condition of moisture equilibrium as specified in Test Method D1412/D1412M.
Analyses of such samples that have been treated in this manner shall be designated as samples equilibrated per Test Method
D1412/D1412M.
7.1.7 Equilibrium moisture results for suspected lignite and subbituminous coals shall be adjusted utilizing the procedure outlined
in Test Method D1412/D1412M, Appendix X1 to estimate inherent moisture content.
7.1.8 The assessment of whether the as-received basis moisture in a sample is equivalent to inherent moisture is a key criterion
when classifying coal on the moist basis. Samples may be at their inherent moisture level, or may be above or below.
7.1.8.1 If the surfaces of sample pieces appear wet, the total moisture present is in excess of inherent moisture. Possible sources
of that moisture may include groundwater contamination, precipitation on the coal, contamination of coal drill core samples by
drilling fluids and additives, and fresh water used to clean the core. Make note of any visible water on the surface of the coal. Break
all larger sample pieces into smaller fragments (particularly if obtained from core) to inspect for visible water occurring in internal
cleats, fractures, voids, etc. Any visible water indicates a total moisture content in excess of inherent moisture.
7.1.8.2 If the surfaces of sample fragments appear dry, the total moisture present may be the full complement of inherent moisture
or somewhat less than that amount. In Appendix X1 of Test Method D1412/D1412M, the section titled Characteristics and
Conditions of Sampling Locality describes a simple field test that can help determine which case is at hand.
D388 − 23
NOTE 2—ASTM Manual 11 provides additional useful information regarding the sampling and handling of core samples.
7.2 Other Types of Samples—A standard rank determination cannot be made unless samples have been obtained in accordance
with 7.1. However, the relation to standard determinations may be usefully given for other types of samples taken under
unspecified conditions, providing the same standards of analysis and computation are followed. Designate these comparative
indications as apparent rank, which indicates the correct relative position for the sample analyzed but does not imply any standards
of sampl
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