Updated: May 28, 2020
If yiu are a beginner in mediiation, say have less than 2 years experinece, I advise you not to touch the C1 (root chakra) from the start unless you want to risk serious issues ...
Fortunately the root chakra is the most closed of all chakras at normal 3D vibration embodied souls, it’s open just around 5%, so to open up to 100% is extremely difficult. Actually it cannot be open 100% for such low body vibrations as the usual 3D person is.
It is true that once in one billion cases maybe there are documented spontaneous inner combustion cases, when a non-spiritual person just bursts into flames and is consumed in minutes because of “accidental” kundalini surge upwards the spine. But the probability for such a misfortune increases a lot by many orders of magnitude if one plays the “wizards apprentice” and rasps it.
How you know you got the C1 really open at least say 50%, which is a lot? Well, there are several signs like often jolts of energy through the spine, body starts to feel different like not so rigid anymore kind of made of plasticine whatever your age is, activation of “lower siddhis” (corresponds to chakras C1-C3) like starting to see in a wider range of frequencies (e.g. seeing entities), start to feel energy movements of Mother Earth (since you opened link to Her now), forecast major Earth events not known by normal people, move energy through your body just by intent, talk easily to animals and plants, influence body organs function, etc. At least 4-5 of like these must be activated currently to draw the conclusion that the C1 got activated at least 50% …
These are latent/dormant abilities that thousands of years in the past the ancient druids/shamans for instance were working on life after life to activate, and hence master the nature in service for the tribes they headed … They became very powerful when activating these abilities and that’s why for instance Julius Cesaer gave order to kill them when he invaded Britain in 1st century BC..
Let me tell you that Buddha, Yogananda, Vivekananda and other fully enlightened souls didn’t have their C1 fully open, it was open between 30% and max 50% (actually they didn’t need it more) at the end of their lifes, so why would you dream of opening it more?
After cleansing yourself of lower beliefs and opening more than 50% your other higher chakras (C2-C7) you can work safely to open your C1 more to ensure a higher flow of Earth energy in your body which is useful obviously.
But striving to open it more than say 30-50% has no purpose in general.