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8 Secondary Ventilation
Fig. 8.1 Side view of a
forcing ducted fan: a single,
b double and c multiple
a)
b)
c)
Fig. 8.2 Side view of the
dead zone (a), ventilated
zone (X) and recommended
duct-to-face distance (d) in
the forcing system for a
development heading
a
X
L 0
maximize the ventilated zone, the duct outlet must be placed at distances (d) ≤ 15 m.
A common recommendation is that d ≤ 4
√
S or d ≤ 6
√
S where S is the face cross
section in m
2 (e.g. Borisov et al. 1976, p. 381).
1 In Europe, most legislation requires
that d ≤ 5
√
S. Higher values of duct-to-face distance increase the role that natural
diffusion plays at cleaning this zone. Certain foreign regulations use the diameter of
the duct to calculate d setting it at 10–15 times this value (Kissell 2006).
There is an additional requirement in the case of coal mining for the airflow rate
through the main gallery to be at least 1.3 times as big as the airflow rate through the
forcing system (e.g. ASM-51, RGNBSM-IT.05.0.03).
1 The smaller the duct-to-face distance the more likely it is that the duct will be damaged during
blasting.