8.3 Required Airflow Rate at the Face
295
this time considering only the volumes of CO and H 2 S produced. In this case, three
categories are established:
• Category 1 (<22.5 l gases kg
−1 explosive): Can be used in all types of underground
works.
• Category 2 (22.5–47.2 l gases kg
−1 explosive): Can be used in well-ventilated
areas.
• Category 3 (47.2–94.85 l gases kg
−1 explosive): Only suitable for surface blasting.
The European standard (EN 13631) does not set limits on the amount of gases that
mining explosives can emit. This duty is left to national authorities. Polish regulations
state that explosives used in mines must not produce more than 0.016 m
3 kg
−1 of
NO X and 0.027 m
3 kg
−1 CO. In Belgium, Slovakia, France and the Czech Republic,
a limit of 0.05 m
3 kg
−1 has been established for the total volume of gases that can
be emitted by a given explosive (Zawadzka-Małota 2015).
8.4 Gas Dilution Models
In this section, we present a number of methodologies used to approximate either
the airflow rate required at the face or if the airflow rate is fixed, the time until an
admissible gas concentration is reached (re-entry time). These approaches can be used
to guague ventilation requirements for the dilution of engine fumes, mine gases (e.g.
CH 4 ), fine dust, as well as blasting fumes. Large differences can be observed between
the values derived from such methodologies and practical realities, particularly in the
case of blasting. Therefore, they should be considered only as approximations to be
used in the conceptual engineering phase, bearing in mind that the only valid approach
to defining a safe time between blasting and allowing the re-entry of personnel is the
measurement of gas concentrations in situ.
8.4.1 Dilution in Steady State
In general, the concentration of gases within a mining room (chamber) generated by
either the processes of combustion or seam leaking increases exponentially, until,
after sufficient time, it stabilizes (Fig. 8.6).
Once a steady state is reached (horizontal asymptote), the gases leave the room
at the same speed at which they are generated. Applying the law of conservation of
mass (Lomonósov-Lavoisier’s law) as illustrated by Fig. 8.7 (Luo and Zhou 2013),
the outward flow rate is balanced by the inward flow rate.
Thus:
Q s = Q v + Q c
295
this time considering only the volumes of CO and H 2 S produced. In this case, three
categories are established:
• Category 1 (<22.5 l gases kg
−1 explosive): Can be used in all types of underground
works.
• Category 2 (22.5–47.2 l gases kg
−1 explosive): Can be used in well-ventilated
areas.
• Category 3 (47.2–94.85 l gases kg
−1 explosive): Only suitable for surface blasting.
The European standard (EN 13631) does not set limits on the amount of gases that
mining explosives can emit. This duty is left to national authorities. Polish regulations
state that explosives used in mines must not produce more than 0.016 m
3 kg
−1 of
NO X and 0.027 m
3 kg
−1 CO. In Belgium, Slovakia, France and the Czech Republic,
a limit of 0.05 m
3 kg
−1 has been established for the total volume of gases that can
be emitted by a given explosive (Zawadzka-Małota 2015).
8.4 Gas Dilution Models
In this section, we present a number of methodologies used to approximate either
the airflow rate required at the face or if the airflow rate is fixed, the time until an
admissible gas concentration is reached (re-entry time). These approaches can be used
to guague ventilation requirements for the dilution of engine fumes, mine gases (e.g.
CH 4 ), fine dust, as well as blasting fumes. Large differences can be observed between
the values derived from such methodologies and practical realities, particularly in the
case of blasting. Therefore, they should be considered only as approximations to be
used in the conceptual engineering phase, bearing in mind that the only valid approach
to defining a safe time between blasting and allowing the re-entry of personnel is the
measurement of gas concentrations in situ.
8.4.1 Dilution in Steady State
In general, the concentration of gases within a mining room (chamber) generated by
either the processes of combustion or seam leaking increases exponentially, until,
after sufficient time, it stabilizes (Fig. 8.6).
Once a steady state is reached (horizontal asymptote), the gases leave the room
at the same speed at which they are generated. Applying the law of conservation of
mass (Lomonósov-Lavoisier’s law) as illustrated by Fig. 8.7 (Luo and Zhou 2013),
the outward flow rate is balanced by the inward flow rate.
Thus:
Q s = Q v + Q c