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Sulphide Waste Dumps Dangers (6 replies)
For those wishing to understand the Sullivan Mine accident, I recommend the attached link.
We need to be clear that the cause of the fatalities was anoxia in a confined space. The paper by Hockely et al. analyzes the roles of geochemistry (sulfide oxidation), the hydrodynamics of the dump with respect to the sampling point and seasonality, and the details of the construction of the sampling point. There also were some general issues of confined-space control and entry (including during rescue) that always need reinforcement.
This is a serious matter in specific conditions and circumstances, but there is no general threat to the atmosphere. New tools to better understand the potential hazards are always welcome.
Thank you for your comment and addressing some of the important issues.
To complete the background, all of the papers and reports that are publicly available on the Sullivan mine accident can be found in this website: http://blogs.ubc.ca/confinedspaceriskassessment/
The Sullivan tragedy can be related to specific conditions after the fact, although we need to consider all of the situations that might create hazardous conditions at some point in the life of the dump. For example oxygen-depleted gas can be trapped in other enclosed structures such as a depression on the ground or a valley. As a result, conducting a risk assessment is necessary to understand the conditions that create hazardous situations.
The paper by Hockley et al. (2009) has applied simplified models which are limited in modeling the gas flow rate regarding the heterogeneous environment of the dump - as mentioned by the authors. For example, calculation of oxidation rate and oxygen depletion is only possible for fine grained homogenous materials. And I guess other calculations are for an ideal gas. What is important is that Hockley et al. (2009) have demonstrated that all sulfide waste dumps can create oxygen-depleted gas. The oxygen-depleted air, if emitted from the dump and becomes confined in an enclosed area, can pose significant risk to the life of workers.
I have developed an Atmospheric Fuzzy Risk Assessment (AFRA) methodology and prototype software to rank the atmospheric risk based on dump and environmental properties (for details please refer to:http://www.sciencedirect.com/science/article/pii/S095042301200174X). AFRA is an expert system based on fuzzy logic. It does not suffer from the limitation of simplified traditional mathematical models and is able to model the nonlinear process of oxygen-depletion where many factors play a role. AFRA is a knowledge-based system which makes decisions about dangerous or safe conditions in a waste dump based on current findings related to the accident and sulfide dumps. Therefore, it can become smarter as we gain more knowledge about atmospheric hazard of waste dumps or as we discuss the model with more experts in the field and incorporate their knowledge. New rules can be added to the system and inference equations and heuristic formulas can be updated to make decisions about atmospheric hazard at confined spaces around sulfide waste dumps. The inputs to the software are linguistic values or numerical values and the model is not affected as much by gaps in the knowledge or data.
According to Hockley et al. 2009, other waste dumps may also pose the same hazard depending on their internal temperature value. AFRA has the ability to interpret the range of internal temperature applying heuristic formulas and weighted inferencing from other dump parameters. The non-linear formulas that derive the internal temperature contain a number of weights that have been derived by validating the model on a number of waste dumps which had known internal temperature value.
Despite AFRA’s ability to determine the internal temperature and assessing the risk, the prototype needs further studies/tests in order to become more reliable for application at mine sites. This is mainly because AFRA is a knowledge-based system and testing it on a few more dumps and adding further experts' knowledge will update the weights and formulas to increase the accuracy of the estimations.
So called White Damp can be very dangerous. Don't know if this is the cause, but it is a recognized hazard underground in mines.
The internal T of white dump is >44 degrees Celsius, therefore considering a summer day with average T of about 38 degrees Celsius, the gas velocity will be positive very small at the toe of the dump (positive means going int the dump). Therefore, the risks of enclosed structures located at the toe which are atmospherically connected to the dump are only a problem and is not hazardous. I have considered the risk for day time in the summer, since this is the worst case scenario (the hottest time in the year).
The risk at Sullivan was not at the hottest time of the year it was instead at an inflection of both temperature and of moisture. The gas flux into the dump reversed due to recent rainfall which reduced the permeability in the ET cover and this coupled with warming external temperatures caused down flow of de-oxygenated gases that were denser than surrounding air.
That is true. The risk at Number 1 Shaft Dump was high during May (the time of accident). However, the risk would be higher during the Summer.
It is now apparent that sulphide waste dumps are associated with an unrecognized atmospheric hazard. Following the confined space accident at Sullivan mine, it became apparent that sulfide waste dumps are associated with an unrecognized atmospheric hazard. Various future changes in the properties of the dump as well as its environment affect the atmospheric risk, which if remained unrecognized can result in major damage to the health of mine employees and the public at large. To reduce the risk, potential failure conditions should be quantified to provide assurance for satisfactory and reliable performance of the dump.
I have developed a software to assess the risk of fatality due to this hazard at various locations around the dump. The software can predict when throughout the year the level of risk may increase to hazardous level. This can help to recognize the high risk places and mitigate the risk in these areas to prevent fatalities due to exposure to hazardous gases. This is an early stage screening tool for atmospheric risk of sulfide waste dumps and can reduce the costs related to possible fatalities and injuries at mine sites.
I am currently looking for potential industrial interest in my software. I am also seeking industrial feedback to improve the software.