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2 Environmental Conditions in the Mine
• In certain cases, the real risk is the displacement of O 2 by another gas such as N 2 ,
rather than the presence of a specific gas.
• Toxic gases should always be monitored at human head height due to the effects
of stratification.
• The exception to the previous rule is the case of flammable gases; it is more logical
to monitor these gases in areas of predominant concentration.
There are four basic options for determining the concentration of gases inside
mines: reactive tubes, specific detectors, multigas detectors and chemical analysis.
2.3.1 Reactive Tubes
This method of gas detection is not common nowadays. A reactive tube is a glass
ampule inside which there is a reagent that reacts in the presence of a particular gas.
The procedure consists of breaking the ampoule at both ends, performing from 3 to
10 strokes with the bellows (Fig. 2.3) and finally reading the concentration in the
coloured area of the ampoule after a couple of minutes. There are tubes of this type
for most of the gases in the mine.
Fig. 2.3 Reactive tube for gas measurement