Currently, techniques used to determine whether or not there is a concealed fire in an inaccessible area of a coal mine are not definitive. Inaccessible areas of coal mines include:

1. A mined-out area, such as a long-wall gob.
2. A mine area, or entire mine, that has been sealed to extinguish a fire.
3. The interior of pillars in a mine.
4. Abandoned mines.

Mined-out areas — gobs — are particularly problematic. The standard practice is to obtain measurements for certain gas concentrations from an inaccessible area, and to apply certain rules to the obtained concentrations in order to try to decipher whether or not there is a fire in the area. Unfortunately, none of the gas measurements, and the associated rules that are applied, are free of potential problems. Therefore, there is always some degree of uncertainty in any decision that is based on the current methods.

A more definitive method of determining whether or not a concealed fire exists would be valuable; perhaps avoiding unnecessary exposure of miners to risks, and unnecessary exposure of mining companies to economic loss. This study details the inadequacies of the current methods for determining the presence of a fire in an inaccessible area of a coal mine, and proposes two novel methods for overcoming the current inadequacies.

The first method that was studied involves looking for the presence of the radioisotope carbon-fourteen in the carbon monoxide in the return airways of coal mines. For the vast majority of coal mines, if there is no fire anywhere in the coal mine, carbon monoxide should not have any carbon-fourteen in it. If there is a fire, the carbon monoxide should have carbon-fourteen in it. This method is based on the Boudouard Reaction, which documents a reaction between carbon, carbon monoxide, and carbon dioxide that only occurs at temperatures that only occur with a fire. Because of the very small amounts of carbon-fourteen in carbon dioxide in the atmosphere, and the small amount of carbon monoxide usually present in a coal mine atmosphere, there does not appear to be any way, currently, to implement this method. Instrumentation that may allow implementation of this method, in the future, is discussed.

The second method, that was studied, involves introducing a select, gaseous, organic compound into an inaccessible area; and then using a gas chromatograph to test for the presence of definitive fire decomposition products of the initial organic compound in the atmosphere that is exiting the inaccessible area.

Laboratory tests, conducted as part of this study, established the concept of this novel method of using select, organic compounds for definitively determining whether or not a concealed fire exists in an inaccessible part of a coal mine. Based on an initial screening of 5 different compounds, two compounds have been selected for use as 'fire indicator gases' with the acronym of 'FIGs.' These two compounds are:

1. C6-Perfluoroketone (CF3CF2C(=O)CF(CF3)2 )
2. 1,1 Difluoroethane (CH3CHF2)

This study provides suggestions as to how to look for other potential FIGs, and how to improve the testing of potential FIGs.

Examples of all four of the types of inaccessible areas listed above are discussed, particularly from the viewpoint of how FIGs could be utilized in each case, and how FIGs could provide better information in each case.

In addition, as a by-product of the experiments conducted for this work, this study identifies at least six gases that might be used simultaneously as tracer gases for complex ventilation studies in a mine, or elsewhere.