7.11 Fire-Fighting Techniques
279
• High operating costs (approximately twelve staff required for one twenty-fourhour period) and maintenance.
• A requirement for highly specialized equipment to implement the procedure.
• The gas stream contains O 2 concentrations of between 1 and 3%.
• Inert gases usually move through the mine at a temperature of up to 90 ºC, making
it harder to extinguish a fire.
Nitrogen
Initially, the use of N 2 was based on accumulated experience with CO 2 . Nitrogen is
generally preferred because (Ray and Singh 2007):
• It has a specific weight similar to, but slightly lower than, air.
• It is injected at low temperatures, which results in the cooling of the burned areas.
• It is easy to produce and its logistics are simple.
• It is not toxic.
• It is inert.
• It effectively displaces O 2 .
• It lessens the chances that the atmosphere will be explosive.
• It can be used in areas that were sealed by the presence of fires.
• It helps to control spontaneous coal combustion.
• It is supplied as cold gas.
However, despite the above, there are multiple disadvantages to this approach:
• It cannot be stored for long periods, so it is sometimes not possible to obtain with
any ease the large quantities needed at the time of a fire.
• It is more expensive than inert combustion gases, which can also be used for
extinction, although definitely cheaper than CO.
• In many cases, there are inherent difficulties in transporting this gas into the mine
from outside.
7.11.2 Dynamic Pressure Balancing
Areas of the mine that are affected by fires are isolated, for example, by means of
explosion-resistant barriers. However, no matter how well constructed these may be,
there will almost always be air leaks that can eventually lead to a revival of the fire. In
order to avoid this phenomenon, additional walls are constructed, creating chambers
in which the existing pressure is monitored by means of sensors that function by
injecting N 2 if the pressure drops (Fig. 7.9). The procedure used to balance these
pressures is called dynamic balancing. It is widely used in coal mining.
279
• High operating costs (approximately twelve staff required for one twenty-fourhour period) and maintenance.
• A requirement for highly specialized equipment to implement the procedure.
• The gas stream contains O 2 concentrations of between 1 and 3%.
• Inert gases usually move through the mine at a temperature of up to 90 ºC, making
it harder to extinguish a fire.
Nitrogen
Initially, the use of N 2 was based on accumulated experience with CO 2 . Nitrogen is
generally preferred because (Ray and Singh 2007):
• It has a specific weight similar to, but slightly lower than, air.
• It is injected at low temperatures, which results in the cooling of the burned areas.
• It is easy to produce and its logistics are simple.
• It is not toxic.
• It is inert.
• It effectively displaces O 2 .
• It lessens the chances that the atmosphere will be explosive.
• It can be used in areas that were sealed by the presence of fires.
• It helps to control spontaneous coal combustion.
• It is supplied as cold gas.
However, despite the above, there are multiple disadvantages to this approach:
• It cannot be stored for long periods, so it is sometimes not possible to obtain with
any ease the large quantities needed at the time of a fire.
• It is more expensive than inert combustion gases, which can also be used for
extinction, although definitely cheaper than CO.
• In many cases, there are inherent difficulties in transporting this gas into the mine
from outside.
7.11.2 Dynamic Pressure Balancing
Areas of the mine that are affected by fires are isolated, for example, by means of
explosion-resistant barriers. However, no matter how well constructed these may be,
there will almost always be air leaks that can eventually lead to a revival of the fire. In
order to avoid this phenomenon, additional walls are constructed, creating chambers
in which the existing pressure is monitored by means of sensors that function by
injecting N 2 if the pressure drops (Fig. 7.9). The procedure used to balance these
pressures is called dynamic balancing. It is widely used in coal mining.