FATAL coal mine accidents over the past month in West Virginia and China offer a grim reminder of how difficult it can be to reach workers underground when their usual route to the surface is cut off. In many such accidents, even the best rescue technology can fail to get to people quickly enough 鈥� so how could it be improved?
When people are trapped below ground, it can often be a race against time for the rescue teams above them to drill narrow boreholes through which they can lower food and water, blow in oxygen, or suck out dangerous gases such as methane or carbon monoxide.
Though no two mines are alike, it typically takes 10 hours to bore every 300 metres. Conventional rotary drills are limited in how fast they can cut, and they slow right down when drilling through granite or other hard rock. In 2007, a rescue effort at the Crandall Canyon mine in Utah failed after it took about 40 hours to drill 500 metres. Nine miners and rescue workers died.
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A 鈥渟uperdrill鈥� now under development could help. On 30 April, researchers at in New Mexico are due to deliver preliminary results to federal mine safety officials on a drill that can penetrate hard rock . 鈥淚t can go through granite like it鈥檚 cutting butter,鈥� says Gerald Finfinger of The National Institute for Occupational Safety and Health (NIOSH), the US federal agency that is funding Sandia鈥檚 research. 鈥淚n a normal drill operation, you could sit there and read a book and barely see it penetrate.鈥�
In laboratory tests, Sandia鈥檚 high-speed drill bored a hole 10 to 15 centimetres in diameter through 30 centimetres of granite in 6 seconds. This means it should be able to penetrate 300 metres of hard rock in under 2 hours.
Unlike the shearing or chipping employed by conventional rotary drills developed for the oil and gas industry, the new drill employs a high-powered pneumatic jackhammer with button-shaped tungsten carbide bits to fracture the rock and break it into a fine powder.
The drill could be available for mine rescues within two years. However, it wouldn鈥檛 have significantly changed the outcome in West Virginia, where rescue teams were able to drill down in a relatively short time, or China, where many miners escaped through partially flooded mineshafts.
NIOSH has also commissioned Sandia to develop a robotic scout that rescue teams could send into a mine to check for survivors and assess whether it is safe to enter. The plan now is to test it under realistic conditions with a mine rescue team. Finfinger says that if it is to be of any use, 鈥渋t has to make rescue faster or safer鈥�.
