Choice of method

UNDERGROUND MINING

Figure 4.1.1 shows the decision tree for underground coal mining activities. For countries with underground mining, and where mine-specific measurement data are available it is good practice to use a Tier 3 method. Mine-specific data, based on ventilation air measurements and degasification system measurements, reflect actual emissions on a mine-by-mine basis, and therefore produce a more accurate estimate than using Emission Factors.

Hybrid Tier 3 - Tier 2 approaches are appropriate in situations when mine-specific measurement data are available only for a subset of underground mines. For example, if only mines that are considered gassy report data, emissions from the remaining mines can be calculated with Tier 2 emission factors. The definition of what constitutes a gassy mine will be determined by each country. For instance, in the United States, gassy mines refers to coal mines with average annual ventilation emissions exceeding the range of 2 800 to 14 000 cubic meters per day. Emission factors can be based on specific emission rates derived from Tier 3 data if the mines are operating within the same basin as the Tier 3 mines, or on the basis of mine-specific properties, such as the average depth of the coal mines.

When no mine-by-mine data are available, but country- or basin-specific data are, it is good practice to employ the Tier 2 method.

Where no data (or very limited data) are available, it is good practice to use a Tier 1 approach, provided underground coal mining is not a key sub source category. If it is, then it is good practice to obtain emissions data to increase the accuracy of these emissions estimates (see Figure 4.1.1).

POST-MINING

Direct measurement (Tier 3) of all post-mining emissions is not feasible, so an emission factor approach must be used. The Tier 2 and Tier 1 methods described below represent good practice for this source, given the difficulty of obtaining better data.

LOW TEMPERATURE OXIDATION

Oxidation of coal when it is exposed to the atmosphere by coal mining releases CO2. This source will usually be insignificant when compared with the total emissions from gassy underground coal mines. Consequently, no methods are provided to estimate it. Where there are significant emissions of CO2 in addition to methane in the seam gas, these should be reported on a mine-specific basis.

ABANDONED UNDERGROUND MINES

Fugitive methane emissions from abandoned underground mines should be reported in Underground Mines in IPCC Category 1.B.1.a.i.3, using the methodology presented in Section in 4.1.5.

Figure 4.1.1 Decision tree for underground coal mines

Figure 4.1.1 Decision tree for underground coal mines

Box 4: Hybrid Tier 2/Tier 3

Note: See Volume 1 Chapter 4, "Methodological Choice and Key Categories" (noting section 4.1.2 on limited resources) for discussion of key categories and use of decision trees

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