A successful rescue operation by NDRF and SDRF teams has led to the extraction of all the 41 workers who were trapped inside the Silkyara tunnel in Uttarakhand.
The authorities, till now, have used multiple techniques to bring the workers out of the tunnel section.
Among the different rescue techniques, rat-hole mining (manual drilling) is considered to be the most dangerous and risky.
Rat-hole miners were the last resort of the rescue operation after the US-made auger machine was extracted from the tunnel after it went kaput.
Rat-hole mining is a method of taking out coal by digging small pits.
It involves manually digging up small tunnels, around 3-4 feet, through which workers enter and extract coal.
But it was banned by NGT in 2014 as a coal-extracting method for being unscientific.
Rat hole mining is largely prevalent in Meghalaya, particularly West Jaintia Hills, East Jaintia Hills and West Khasi Hills.