Review Reports

Review

Response

The authors should provide more detailed information on the experimental setup, including the dimensions of steel tubes, charge parameters, and priming details, to improve the repeatability of the tests.

Thank you for this comment. Such details are graphically explained in figures 5 and 6, where dimensions of steel tubes, charge parameters, and priming details are given. We understand that the figures may appear not of good quality or perfectly readable in the PDF provided for review, but we assure are of good quality and readable in the manuscript sent to the journal

It is suggested that the in-situ measurement conditions in production tunnels be further described, such as geological characteristics and confinement environments.

Thank you for this suggestion. We have revised the manuscript to include a detailed description of the geological and geomechanical conditions of the production tunnel where the in-situ VOD measurements were conducted. The added text is located in lines 233–251

The authors should further discuss the influence of different initiation systems, and compare their differences.

Thank you for this comment. That would be interesting if the miners used more than one initiation system, but they don’t they use exclusively the one described in the manuscript. The purpose of the study was the analysis of AN behavior specifically in the conditions used by artisanal miners. Also, as reported in the section “Tests in production tunnels within ASM operations”: “Attempts to modify […] were therefore unsuccessful”

Some descriptions of the experimental phenomena can be more concise and standardized to improve the readability and academic rigor of the manuscript.

Christian

This study can be improved by adding more discussion on the critical initiation conditions for AN without FO.

Thank you for this comment. We agree that further discussion of the critical initiation conditions strengthens the interpretation of our findings. However, specific experimental data addressing the critical initiation behavior of AN are scarce in the literature. For this reason, we incorporated studies on ANFO as a reference framework, given its compositional similarity and established diameter-dependent detonation limitations. These additions have been incorporated in lines 478–489 of the revised manuscript.

Review

Response

The total sample size of nine detonations is insufficient to derive statistically significant conclusions about explosive performance.

Thank you for this important comment. It is true that nine is a limited number of tests. Nevertheless, considering real-scale application on field, and given all the constraints of field work in the sector of artisanal miners, nine tests can be considered significant, specially considering that we were studying the performance of AN without FO specifically under artisanal mining installation conditions, and not AN behavior in general,

The study lacks a control group using standard ANFO to establish a performance baseline for the rock conditions.

Thank you for this important comment. This is true. Nevertheless, that would be impossible to achieve in the field, in the location of the experiments, as the miners refuse to employ standard ANFO. Operational use of standard ANFO under similar diameters and priming is described in the cited work by Seccatore et al. “Seccatore, J., Gonzalez, P. & Herrera, M. Peculiarities of drilling and blasting in underground small-scale mines. REM Int. Eng. J. 73, 387–394 (2020).”

The physical and chemical properties of the "agricultural-grade" ammonium nitrate (e.g., porosity, density, coating) are not characterized.

Thank you for this observation. We have now included a description of the physical and chemical properties available from the manufacturer’s technical sheet of the agricultural-grade ammonium nitrate used in this study (granulometry 1–4 mm, 34% nitrogen content, high water solubility). We also clarify that parameters such as porosity, bulk density, oil absorption capacity, and coating composition are not specified by the manufacturer, as the product is formulated as a fertilizer rather than as an explosive-grade material. These additions have been incorporated in the Materials and Methods section (lines 170-181).

The potential influence of moisture contamination is not adequately ruled out, given the wet appearance of cartridges in Figure 3.

Thank you for this comment. As specified in the caption of Figure 3, “The paper cartridge appears wet due to incidental contact with water during handling for photographic documentation; wet AN does not react and such cartridges are not used for charging.” AN is always used only in dry conditions, otherwise only emulsion is employed.

The impedance mismatch between the steel tubes used in testing and the actual rock mass is not addressed.

Thank you for this important comment. This is true. Being the two tests (tube Vs. rock) completely different in terms of charging (considering the irrational AN-Emulsion-AN used by miners in tunnel faces), comparing the impedances appeared to be meaningless for the purpose of the study.

Several VOD records exhibit unexplained signal noise and zero-reset anomalies that are not sufficiently analyzed (e.g., Figure 8).

Thank you for this important technical observation. The VOD measurements were performed using a ProbeRod HS system with coaxial cable data transmission, which is specifically designed for short-column in-hole explosive tests such as those conducted in this study. The abrupt vertical drops and zero-reset segments observed in some of the distance–time traces are interpreted as instrumental artifacts rather than physical re-initiation events.

Under underground field conditions, transient signal interruptions may occur due to mechanical disturbance of the probe, fragmentation-induced strain on the coaxial cable, or temporary loss of electrical continuity caused by shock and gas expansion. These effects are known to occur particularly in short-charge configurations.

We have now clarified this point in the manuscript (lines 530–535).

The high-explosive emulsion primer constitutes a disproportionately large fraction of the total charge energy in these short holes.

Thank you for this comment. This is true. And yet, this is the real charging condition used by the miners. The purpose of the study was the analysis of AN behavior specifically in the conditions used by artisanal miners

The 2015 m/s velocity recorded in "Hole 2" is summarily dismissed without discussing potential Low Velocity Detonation (LVD) regimes.

Thank you for this insightful comment. We agree that the recorded velocity of approximately 2015 m/s in Hole 2 requires further clarification. Although this value is significantly lower than the nominal steady-state detonation velocity of the emulsion explosive (~5000 m/s), detonation did occur. To address this point, we have revised both the Results (lines 420–426) and the Discussion (lines 491–497) sections. In the Results section, the description of Hole 2 has been reformulated to avoid classifying the event as “no detonation” and instead to describe it as non-ideal propagation. In the Discussion section, we now explicitly address the possibility of low-velocity or near-critical detonation regimes and clarify that the reduced velocity is interpreted as a non-ideal or transient velocity deficit influenced by geometric configuration and confinement conditions

The 0.90 m sensor length is insufficient to monitor the full 1.20 m blasthole depth, creating significant data blind spots.

Thank you for this comment. It would seem so, if not for the reason given by operational constraints described in the text: “As the tests were conducted within an active artisanal mine and executed by the mine’s own operators, the experimental configuration necessarily followed the established local practice. When questioned, miners stated that alternative, technically conventional charging configurations were avoided because, in their experience, “otherwise it does not go off.” Attempts to modify this practice were therefore unsuccessful. To preserve the representativeness of the field conditions, the PROBEROD sensor was inserted only from the primed cartridge up to the collar of the hole.”

The manuscript fails to physically explain the paradox between the experimental "failure" and the widespread, successful adoption by miners.

We thank the reviewer for this comment. Yet, the manuscript offers explanations to the effective rock breaking by AN without FO: “Instead, the subsequent reaction within the AN column may correspond to one of the following behaviors:

•             deflagration,

•             slow combustion, or

•             absence of observable reaction.

The breakage of the steel tubes beyond the level of the primer (from about ¼ to about ½ length of the AN charge) demonstrates that some high pressure is exerted by the AN, therefore excluding the latter behavior”

Quantitative data on rock fragmentation, muck pile throw, or excavation results are entirely absent.

Thank you for this observation. We agree that including quantitative fragmentation data strengthens the practical interpretation of the blasting results. We have now incorporated a quantitative rock fragmentation analysis based on digital image processing using WipFrag software. Representative particle size distributions (P50 and P80 values) have been included.

These additions have been incorporated in Section 2 (Materials and Methods), lines 305–311, and in the Results section, lines 366–377.

Post-blast toxic fume concentrations (NOx) were not measured, despite the introduction citing ventilation reduction as a primary motivation.

Thank you for this important observation. The reference to ventilation and toxic fumes in the Introduction was included to highlight one of the operational reasons reported in the literature for the replacement of ANFO by fertilizer-grade ammonium nitrate (AN) without fuel oil in artisanal underground mining. The elimination of fuel oil has been empirically associated by miners with reduced blasting fumes and shorter ventilation shifts.

To clarify this aspect and provide technical support beyond empirical observation, we have now cited an independent undergraduate thesis conducted under my supervision in the same mining sector and under comparable operational and ventilation conditions (Mojarrango Vallecilla, 2023). In that study, air quality monitoring was performed in four underground zones, and nitrogen oxides (NOx), specifically NO₂, were measured using portable electrochemical sensors. The results indicated that NOx concentrations remained within applicable occupational exposure limits during standard working shifts.

This reference has now been incorporated into the Introduction (lines 80-84)

The safety risks associated with the documented "reverse priming" practice (primer above the charge) are not critically evaluated.

Thank you for this comment. Indeed, the “reverse priming” (AN-emulsion-AN) can produce partially non detonated charges. This event has never been detected, as normal measurements only show remaining depths of unbroken holes but where the charge reacted and dissipated. Nevertheless, the rick of a partial misfire is present.

We address now this in the text (lines 234-238).

Figures 9 through 15 are raw software screenshots containing irrelevant interface elements rather than properly formatted scientific plots.

Thank you for this comment, but we respectfully disagree. Figures 9 through 15 are original, elaborated images that show on the left the picture of the intact pipe and the broken pipe, showing the position and height of the priming charge and the length of the broken section of pipe, compared vis-à-vis with the VOD reading in scale.

The discussion lacks theoretical depth regarding the critical diameter constraints of agricultural ammonium nitrate in 51 mm charges.

Thank you for this precious comment. This is a very good point. Being AN not commonly used as a high, detonating explosive, there is no indication of a specific critical diameter. 51mm is already sub-optimal for standard ANFO. We added this comment in the text (lines 134/138)