294
8 Secondary Ventilation
• The carbon content of explosives is a dimensionless value, α, which varies between
0.04 and 0.17. A table was provided for the various explosives in use at the time.
4
• The gas throwback region (L o ) is about 50 m long.
• If p is the mass in kg of explosive used per m
2 of face section (S), then the product
of these values gives the total mass of explosive needed for blasting. Multiplying
this value by the carbon content of the explosive (α), gives the mass of carbon that
reacts in the explosion. If this value is divided by the mass of a mole of carbon
5
and multiplied by 22.4 l (the volume occupied by a single mole of gas at STP), the
volume of carbon gases generated is obtained. This, divided by the initial volume
of the throwback region (S L o ) is the initial concentration. Therefore, the total
carbon content (CO + CO 2 ) of the blasting fumes is close to 0.0375αp. The ratio
of CO 2 to CO in the fumes is 2:1, thus the concentration of CO will be 0.0125αp.
Explosives are usually classified according to the volume of fumes they generate.
The MSHA states that the maximum amount of gases produced by Permissible
Explosives in underground coal mines or gas leaking mines must be 156 l kg
−1 .
Such explosives offer security in these conditions as they are designed such that their
flame is of low volume, duration and temperature. These advantages are achieved
through the addition of various salts to the explosive formula. In addition to CO, the
classification considers gases such as CO 2 , H 2 S, NO, NO 2 , NH 4 and SO 2 , through
conversion into their CO equivalent (CO eq ). This conversion is carried out by taking
the quotient of the TLV-TWA
6 for CO and the TLV-TWA for a given toxic gas. The
CO eq for a mixture of gases is found by summing the CO eq values for each gas in
the mixture, thus:
CO eq = 0.01CO 2 + 1CO + 5H 2 S + 2NO + 17NO 2 + 2NH 4 + 25SO 2
(8.7)
After applying this expression, two categories are established:
• A: <78 l CO eq kg
−1 explosive, and
• B: 78–156 l CO eq kg
−1 explosive.
If the explosive generates more than 156 l CO eq kg
−1 then this explosive is deemed
not permissible for underground use in coal mines. The explosive is then re-classified
according to guidelines developed by the Institute of Makers of Explosives (IME),
4 New generations of explosives have reduced the volume of the gases generated.
5 Carbon reacts to form CO 2 or to form CO. One mol of C is required to make one mol of either of
these gases.
6 TWA stands for the Time-Weighted Average.
8 Secondary Ventilation
• The carbon content of explosives is a dimensionless value, α, which varies between
0.04 and 0.17. A table was provided for the various explosives in use at the time.
4
• The gas throwback region (L o ) is about 50 m long.
• If p is the mass in kg of explosive used per m
2 of face section (S), then the product
of these values gives the total mass of explosive needed for blasting. Multiplying
this value by the carbon content of the explosive (α), gives the mass of carbon that
reacts in the explosion. If this value is divided by the mass of a mole of carbon
5
and multiplied by 22.4 l (the volume occupied by a single mole of gas at STP), the
volume of carbon gases generated is obtained. This, divided by the initial volume
of the throwback region (S L o ) is the initial concentration. Therefore, the total
carbon content (CO + CO 2 ) of the blasting fumes is close to 0.0375αp. The ratio
of CO 2 to CO in the fumes is 2:1, thus the concentration of CO will be 0.0125αp.
Explosives are usually classified according to the volume of fumes they generate.
The MSHA states that the maximum amount of gases produced by Permissible
Explosives in underground coal mines or gas leaking mines must be 156 l kg
−1 .
Such explosives offer security in these conditions as they are designed such that their
flame is of low volume, duration and temperature. These advantages are achieved
through the addition of various salts to the explosive formula. In addition to CO, the
classification considers gases such as CO 2 , H 2 S, NO, NO 2 , NH 4 and SO 2 , through
conversion into their CO equivalent (CO eq ). This conversion is carried out by taking
the quotient of the TLV-TWA
6 for CO and the TLV-TWA for a given toxic gas. The
CO eq for a mixture of gases is found by summing the CO eq values for each gas in
the mixture, thus:
CO eq = 0.01CO 2 + 1CO + 5H 2 S + 2NO + 17NO 2 + 2NH 4 + 25SO 2
(8.7)
After applying this expression, two categories are established:
• A: <78 l CO eq kg
−1 explosive, and
• B: 78–156 l CO eq kg
−1 explosive.
If the explosive generates more than 156 l CO eq kg
−1 then this explosive is deemed
not permissible for underground use in coal mines. The explosive is then re-classified
according to guidelines developed by the Institute of Makers of Explosives (IME),
4 New generations of explosives have reduced the volume of the gases generated.
5 Carbon reacts to form CO 2 or to form CO. One mol of C is required to make one mol of either of
these gases.
6 TWA stands for the Time-Weighted Average.