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84 E&MJ; • DECEMBER 2014 www.e-mj.com V E N T I L AT I O N The introduction of diesel-engine vehicles into underground mining in the late 1920s brought with it a whole new set of chal- lenges, not all of which have been addressed completely yet. Locomotives led the way, with the subsequent move toward trackless haulage and personnel transport in both coal and hard-rock mines adding further com- plexity to the situation. National research organizations were, in some respects, well ahead of the game; for example, the U.S. Bureau of Mines began its work on the effects of diesel emissions underground as early as the 1930s. This program continues, under the auspices of National Institute for Occupational Safety and Health (NIOSH), and was reviewed in detail in the Society for Mining, Metallurgy and Exploration (SME) 2010 reference volume, Extracting the Science: A Century of Mining Research . Anyone who has had the experience of working with diesel engines in confined spaces will readily acknowledge that emis- sions can be singularly unpleasant from a number of perspectives. Smoke, smell and eye irritation are the most obvious, and were the first to be tackled in terms of post-combustion treatment. Early solutions focused on technologies such as water- traps, through which the engine exhaust was bubbled, the aim being to grab as much of the visible soot and unburnt fuel as possible. Aside from direct impacts on the indi- vidual, diesel-engine vehicles brought with them wider implications for the design and operation of ventilation systems. Not only did they need additional air in order to run efficiently, but ventilation volumes needed to be increased in order to handle the new source of heat generation and to dilute emissions. And while these issues could be addressed relatively easily in main haulages where airflows were strong, the same could not be said for blind develop- ment ends or drawpoints where the atmos- phere could quickly degenerate as exhaust fumes built up. Auxiliary fan systems pro- vided an answer, with the recent develop- ment of ventilation on demand (VOD) bringing a new level of control to managing air supplies on an as-needed basis while cutting overall ventilation costs. The last time that E&MJ; looked at ven- tilation (December 2013, pp.60–69), mention was made of the increased con- cerns within the hard-rock mining industry of the effects of diesel particulate matter (DPM) on workers' health. This is, of course, by no means confined to the min- ing industry, with widespread recognition of the damaging potential of DPM within society as a whole: one has only to look at requirements for trucks and buses to be equipped with exhaust filters in day-to-day life for that to be apparent. The need for diesel engines to perform better on a number of fronts, including minimizing their emissions, has led to long-term efforts by legislators and manu- facturers alike to achieve specific, staged targets. As the Canadian Institute of Mining (CIM) pointed out in an article in the June/July edition of its magazine earli- er this year, achieving Tier 4 Final compli- ance has been a 20-year task, and while the mining industry has in some respects lagged behind the adoption of each stage on the journey, the manufacturers that sup- ply engines for LHDs and other under- ground vehicles are working hard to trans- fer the new standards to the much heavier- duty mining environment. As the CIM article also noted, from January 2015 every new diesel engine sold in the U.S. will have to achieve a 90% reduction in DPM and nitrogen oxide (NO x ) emissions compared to pre-1996 levels. And while meeting targets like this is hard enough in the open air, the enclosed envi- ronment of an underground mine drift is an even tougher place to achieve compliance. Ventilating for Diesel Particulates With diesel-engine vehicles ubiquitous in underground mining, and Tier 4 Final requirements now in place, research is focusing on how best to operate ventilation systems to handle residual emissions By Simon Walker, European Editor Dirty exhaust streams away from a truck in a small French uranium mine 25 years ago. (Photo: Simon Walker)