Regarding safety: Ketamine is one of the safest drugs in existence, regarding acute intoxication aka OD, but it does show toxicity for kidneys and bladder with chronic use. What it will do to your brain with chronic use is not sure yet.
It is dangerous in the sense that you might take enough to still be able to move but not be coordinated and present enough, so you might fall down, cross the street in a bad moment etc.
You might also get injured and not feel pain in the moment, I saw a guy fall and then go to sleep immediately, then he woke up a couple of hours later and he was crying in pain as he had dislocated a shoulder.
It is also dangerous to mix with opiates.
Theres a few types of ketamine around, mostly it will be Racemic or S+.
Racemic will have more of a paralysing effect when reaching the same effect as S+, but you will need more Racemic than S+ for having the same effect., IE
50mg racemic = 80mg S+ for paralysis
50mg racemix = 33mg S+ for high
(These numbers are just made up to give an example)
Racemic will last more and it will be more likely that you will get nausea.
S+ is more psychedelic.