The Journal of Explosives Engineering - May/June 2022 - 14

A temperature increase is not always associated with this
method of testing and a sample not showing signs of reactivity
does not mean that a hole is not reactive. On bench visual
monitoring of blast holes during charging is recommended to
catch any reactive holes that did not show signs of reactivity
during testing.
Learnings and Recommendations
Due to the serious nature and risk of premature detonations
associated with the use of explosives in the reactive
ground, a risk assessment should be performed at sites where
there is the potential or suspicion of reactive ground. Mine
operators (at proposed and existing sites) should constantly
monitor a checklist of reactive ground indicators. If any of
these indicators are found, then a detailed risk assessment of
the use of explosives on the sites should be carried out. Exiting
the preliminary risk assessment, if reactive ground is identified,
the following controls are highlighted to manage the risk.
* Use urea inhibited bulk emulsion. Urea reduces the rate of
reaction and thus slows heat build-up for a window of time.
* Blocks should be kept small enough so that they can be fully
charged and fired the same day.
* In some instances, holes may need to be sleeved with plastic
liners before charging commences to isolate the explosives
from the borehole walls.
* Drill cuttings must be kept clear of the blast hole collars.
This can be done by the drill assistants clearing around each
collar with shovels to a radius of at least 0.5 m [1.64 feet]
from the blast hole collars. Drill cuttings that mix in with
explosives present a higher risk of rapid temperature buildup.
Clearing the hole collars of drill cuttings will lower the
chance that activity around the hole collar (such as charging
and hole priming) will result in cuttings falling back in the
hole and on top of the explosives column.
* Personnel on the block must be kept to a minimum during
the priming and stemming activities.
* Ensure all explosive and initiation products used to blast
reactive ground are compatible and that the temperature
range for use of each product has been qualified.
* Only top prime.
* Use imported stemming material tested to be free of reactive
ground. Unless stemming can be done rapidly using
a stemming truck, blast holes should remain unstemmed.
Be aware that no stemming in the blast holes may result in
increased air blast and more blasted/flyrock ejection from
surface cratering.
* If the holes need to be stemmed, then they should only be
stemmed as the final activity just before blasting time. In
other words, all holes must remain open for long as possible
to release heat. This reduces the risk of hole deflagration
and/or unexpected detonation.
* Unstemmed holes also facilitate hole observation. Reacting
holes may emit visible yellow-orange-red-brown fumes from
the hole collars. If this occurs, then the blast area should be
immediately evacuated and secured, and personnel moved
to a safe distance.
* Reassess reactive ground potential by risk assessment on a
regular basis.
Acknowledgements
The authors thank the BME Losberg R&D Laboratory, especially
Dr. Bronwynne Victor - R&D Manager and Quentin Steyl
- Senior R&D Chemist, for their continuous assistance in testing
ground samples. The authors also thank Scott Scovira for the editing
and guidance on the paper.
References
1. Dr. Pathak, R. (2016), (Krause. V, Interviewer).
2. Krause. V. (2017) (Internal Reactive Ground Guide)
3. Australian Explosives Industry and Safety Group. (Information
Referral Guide).
4. Van Jaarsveld, P. (2019). BME Technical Training - Chapter 11,
Dealing with Reactive Ground and Hot Holes.
About the Authors
Deon Pieterse is a Technical Services Manager, BME a Member of
the Omnia Group.
Grant Small is a Technical Services Engineer, BME a Member of
the Omnia Group.
This article was presented by Scott Scovira in place of the authors who
were unable to attend at ISEE's 48th Annual Conference on Explosives
and Blasting Technique in January 2022 in Las Vegas, Nevada. This paper
has been updated from its original version. The opinions and ideas expressed
are not necessarily those of the International Society of Explosives
Engineers or the editorial/publishing staff of the Journal of Explosives
Engineering. See " The Proceedings of the 48th Annual Conference on Explosives
and Blasting Technique " for full text and references for this paper.
14
The Journal of Explosives Engineering
May/June 2022
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