278
7 The Role of Ventilation in Fires and Explosions
systems for creating inert atmospheres, dynamic pressure balancing and variation
of the ventilation regime are listed below.
7.11.1 Formation of Inert Atmospheres
This approach seeks to create atmospheres that cannot sustain combustion, including
ignition. This can be achieved in two ways: (a) by increasing the concentration of
flammable gas above its UEL (for example, the injection of a large amount of CH 4
would displace O 2 and prevent combustion); (b) by the addition of an inert gas that
cannot play a part in the combustion process, also displacing O 2 .
Obviously, the second technique is safer, so inert gases are commonly used to
displace O 2 , as a measure to prevent explosions or to inhibit a combustion that has
already begun (McPherson 1993, p. 853). Three gases are currently in use: CO 2 , inert
combustion gases and N 2 .
Carbon Dioxide
As is well known, this gas is denser than air, making it particularly suitable for extinguishing fires in deep areas of mines. The gas helps to put a fire out by cooling and by
displacing oxygen. However, its use suffers from certain disadvantages (McPherson
1993, p. 854):
• It can cause freezing of conduits.
• It is soluble in water, which causes part of it to be lost.
• It is corrosive once dissolved in water.
• It can act as an O 2 donor to fires.
• It does not follow the general circuit of ventilation, tending to accumulate in the
lower zones of the workings.
• It is more expensive than N 2 and inert combustion gases.
• It interferes with the monitoring of the evolution of the fire by means of gas ratios.
• It tends to adsorb to carbonaceous surfaces.
• It can lead to the generation of CO.
Inert Combustion Gases
The group of techniques involving inert combustion gases includes the use of CO 2 ,
H 2 O, N 2 and small amounts of CO and H 2 from combustion. In the early days of this
technique, inert coal combustion gases were used, but today they are obtained from
the combustion gases of kerosene-fuelled jet engines. The gases are subjected to a
previous cooling process and injected into the affected area. The most commonly
used systems today are probably the GAG 3A, named for the Polish initial letters for
gas-to-gas combustion (Mucho et al. 2005) and the Steamexfire, which adds into the
gas stream a large amount of atomized water and steam. Both systems are preferred
to the use of N 2 and CO 2 , as they are able to supply higher airflow rates of inert gas.
Despite this, the group of procedures has the following disadvantages:
7 The Role of Ventilation in Fires and Explosions
systems for creating inert atmospheres, dynamic pressure balancing and variation
of the ventilation regime are listed below.
7.11.1 Formation of Inert Atmospheres
This approach seeks to create atmospheres that cannot sustain combustion, including
ignition. This can be achieved in two ways: (a) by increasing the concentration of
flammable gas above its UEL (for example, the injection of a large amount of CH 4
would displace O 2 and prevent combustion); (b) by the addition of an inert gas that
cannot play a part in the combustion process, also displacing O 2 .
Obviously, the second technique is safer, so inert gases are commonly used to
displace O 2 , as a measure to prevent explosions or to inhibit a combustion that has
already begun (McPherson 1993, p. 853). Three gases are currently in use: CO 2 , inert
combustion gases and N 2 .
Carbon Dioxide
As is well known, this gas is denser than air, making it particularly suitable for extinguishing fires in deep areas of mines. The gas helps to put a fire out by cooling and by
displacing oxygen. However, its use suffers from certain disadvantages (McPherson
1993, p. 854):
• It can cause freezing of conduits.
• It is soluble in water, which causes part of it to be lost.
• It is corrosive once dissolved in water.
• It can act as an O 2 donor to fires.
• It does not follow the general circuit of ventilation, tending to accumulate in the
lower zones of the workings.
• It is more expensive than N 2 and inert combustion gases.
• It interferes with the monitoring of the evolution of the fire by means of gas ratios.
• It tends to adsorb to carbonaceous surfaces.
• It can lead to the generation of CO.
Inert Combustion Gases
The group of techniques involving inert combustion gases includes the use of CO 2 ,
H 2 O, N 2 and small amounts of CO and H 2 from combustion. In the early days of this
technique, inert coal combustion gases were used, but today they are obtained from
the combustion gases of kerosene-fuelled jet engines. The gases are subjected to a
previous cooling process and injected into the affected area. The most commonly
used systems today are probably the GAG 3A, named for the Polish initial letters for
gas-to-gas combustion (Mucho et al. 2005) and the Steamexfire, which adds into the
gas stream a large amount of atomized water and steam. Both systems are preferred
to the use of N 2 and CO 2 , as they are able to supply higher airflow rates of inert gas.
Despite this, the group of procedures has the following disadvantages: