There have been many single and multiple fatalities over generations of underground mining due to workers being gassed by toxic blasting fumes or an irrespirable atmosphere after re-entering the area that was blasted, or some area connected to it. The traditional approach to determining safe re-entry (clearance) times was to use a fixed time interval after blasting based on either experience, limited testing with chemical stain tubes, or simple dilution calculations, as well as training miners to “use their nose” to smell for fumes. With the advent of relatively inexpensive and reliable electronic gas monitors, combined with the now well-established principal of managing risks to the “as low as reasonably achievable” (ALARA) standard, re-entry procedures have been undergoing considerable changes. Gas monitors are now frequently used to test all “potentially” affected locations. However, the risks from migrating blasting fumes have also increased due to the trends to allow or even design ventilation circuits with major short-circuiting through open stopes and other leakage paths, as well as using the main ramp in some mines as a “dirty intake” with one level effectively in series with another. In all of these cases, blasting fumes from one location may be introduced into non-blasted locations. Moreover, the introduction of 12 hour shifts and “long” rosters has created some divergence in the industry with respect to the gas limit standards for “safe” gas levels for re-entry. This paper reviews modern procedures for safe re-entry after both development and production blasting, including how it is being undertaken, the target gases being used for re-entry clearance criteria, and general risk management considerations. It makes recommendations for safe standards.
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