1
24-036
Estimating Air Blast Velocity Using Optical Flow Algorithm
Vasu Gangrade
National Institute for Occupational Safety and
Health, Pittsburgh, PA
ABSTRACT
Large-opening underground stone mines pose significant
ground control challenges, including the risk of massive
pillar collapses. These collapses can result in dangerous air
blasts characterized by tremendous force and high velocity.
Estimating the velocity of these air blasts proves challenging
due to the absence of accurate air velocity instruments near
the mine portals. To address this issue, this paper proposes a
novel approach that leverages closed-circuit television cam-
era footage from the mine. Specifically, it employs the opti-
cal flow algorithm implemented in Python to estimate the
velocity of the air blasts, providing a valuable tool for assess-
ing and mitigating risks in such mining environments.
INTRODUCTION
Underground limestone mines are generally mined using
the room-and-pillar method. As the name suggests, the
method involves forming a grid-like pattern of entries and
crosscuts underground, and the stone deposit is divided
into a series of pillars, which are left standing to support
the roof of the mine. The method is specially challenging
in stone mines as the entry sizes are very large ranging from
40–50 ft wide and 30–40 ft high entries. In addition to the
entries, the underground stone mines also use benching.
Benching involves further excavating the floor of the entries
which increases the development height to 90–100 ft
(Figure 1). Therefore, benching creates tall slender pillars in
the underground stone mines which are high, but less wide
(Figure 2). These pillars often form an hourglass shape and
can collapse if the pillar cannot take the weight of the roof
(Mark and Rumbaugh, 2022).
A pillar collapse happens when an array of pillars fails
suddenly. Pillar collapses can occur with very little warning
and can affect miners far away from the collapse (MSHA,
2023). Several factors can contribute to a pillar collapse,
including excessive mining of adjacent rooms leading to
increased stress on the pillars, geological faults or weak-
nesses in the surrounding rock, changes in the stress dis-
tribution within the mine due to excavation activities or
subsurface factors, and inadequate pillar design or insuf-
ficient pillar size for the load they are supporting.
Pillar collapse in underground stone mines presents
a grave safety concern, as it endangers the lives of miners
working not just in the affected area but everywhere near
the mine. The sudden failure of support pillars can lead
to catastrophic events, including roof collapses and falling
debris, placing miners at immediate risk from the ground
control event. The pillar collapse also leads to the formation
of an air blast.
Figure 1. Typical large-opening stone mine with benching
24-036
Estimating Air Blast Velocity Using Optical Flow Algorithm
Vasu Gangrade
National Institute for Occupational Safety and
Health, Pittsburgh, PA
ABSTRACT
Large-opening underground stone mines pose significant
ground control challenges, including the risk of massive
pillar collapses. These collapses can result in dangerous air
blasts characterized by tremendous force and high velocity.
Estimating the velocity of these air blasts proves challenging
due to the absence of accurate air velocity instruments near
the mine portals. To address this issue, this paper proposes a
novel approach that leverages closed-circuit television cam-
era footage from the mine. Specifically, it employs the opti-
cal flow algorithm implemented in Python to estimate the
velocity of the air blasts, providing a valuable tool for assess-
ing and mitigating risks in such mining environments.
INTRODUCTION
Underground limestone mines are generally mined using
the room-and-pillar method. As the name suggests, the
method involves forming a grid-like pattern of entries and
crosscuts underground, and the stone deposit is divided
into a series of pillars, which are left standing to support
the roof of the mine. The method is specially challenging
in stone mines as the entry sizes are very large ranging from
40–50 ft wide and 30–40 ft high entries. In addition to the
entries, the underground stone mines also use benching.
Benching involves further excavating the floor of the entries
which increases the development height to 90–100 ft
(Figure 1). Therefore, benching creates tall slender pillars in
the underground stone mines which are high, but less wide
(Figure 2). These pillars often form an hourglass shape and
can collapse if the pillar cannot take the weight of the roof
(Mark and Rumbaugh, 2022).
A pillar collapse happens when an array of pillars fails
suddenly. Pillar collapses can occur with very little warning
and can affect miners far away from the collapse (MSHA,
2023). Several factors can contribute to a pillar collapse,
including excessive mining of adjacent rooms leading to
increased stress on the pillars, geological faults or weak-
nesses in the surrounding rock, changes in the stress dis-
tribution within the mine due to excavation activities or
subsurface factors, and inadequate pillar design or insuf-
ficient pillar size for the load they are supporting.
Pillar collapse in underground stone mines presents
a grave safety concern, as it endangers the lives of miners
working not just in the affected area but everywhere near
the mine. The sudden failure of support pillars can lead
to catastrophic events, including roof collapses and falling
debris, placing miners at immediate risk from the ground
control event. The pillar collapse also leads to the formation
of an air blast.
Figure 1. Typical large-opening stone mine with benching