It's definitely not safe. I know two people who are permanently mentally disabled from using LSD.
As opposed to two people that became mentally disabled and just happened to use LSD.
There is an awful lot of paranoid hysteria hype outputted on the subject of the drug. I will tell you what I know from what I've learnt about the substance from before and after use (many years ago).
Firstly the "hype", LSD is a drug that alters the chemistry of brain to the point where neurological stimulation becomes re-pathed to neuron's not necessarily trained for dealing with the stimuli. This is the main reason for altered sensory occurrences and the main reason for all the initial fears of the drug itself.
The hallucinations themselves can be anywhere from mild to strong depending on the overall dosage and one of the main problems with the drug is there is no way to speed up the removal of it from the system, due to it's effect on the brain it can't be "watered down" and passed (urinated or sweated), vomited up or outputted through excrement.
This is the main reason why it's suggested that if you "experiment" that you will be at the beck and whim of your own mind. If you already suffer a paranoid personality then it's possible that such psychotropic (and occasionally used as psychiatric) drugs aren't for you. (in fact if you suffer from Epilepsy I would really suggest staying clear of it)
Psychiatrists will harp on about the potential effects of "Flashbacks", this is where they believe that some random point in the future you could be effected similar to how you were on the drug. Now in the usage of MDMA, it's known that certain "Positive" but incidentally wrongly stimulated neurons can react when stimulated under conditions that were occurant at the time (a bit like triggering an old memory), I've had such "positive" incidences with certain euphoric or trance music played from that decade (if anything it just buys into the whole nostalgia of the period)
Negative occurrences I would suggest would mirror something that "dyspraxics" suffer, where particular materials or sound will cause a nausiating or anxiety effect.
The sorts of flashbacks that the Doctors seem to think occur are like reliving past lives while driving your car home, or forgetting to feed your pets or baby because you were on a different planet. (They seem to have some seriously extreme reasoning for something that they apparently are suppose to understand)
I'd suggest if you are going to experiment with this, you need to do so in the right atmosphere, for instance it's not best to do it alone (but don't peer pressure anyone into joining you), it's best to make sure you are outside for the most part (This lessens any aggrophobic effects caused by visual stimuli concerning room size, shape or patterning), it's best not to be anywhere too crowded with "Normal" people. (The last thing you want is stumbling mis-stimulated words in incoherent rants at people that you might have to deal with the day later.)
Above all it's best to do it where you feel safe, secure and can feel that you can have fun. (This will lessen the any chance of neurological anxieties shaping your "trip".)
The best place I actually found back in the day was spending the evening/night and morning at the beach, but this could also work in the countryside etc. Just don't lose your car!!!.
Obviously such "Experiments" are best not done too Scientifically and are actually better more sporadically since it's more spontaneous and more fun. (try an icecream
Just one thing to note, I don't support drug use, however the one off experiment is what it's all about because it's a personal experience builder and should some pain in the ass spike your drink in the future or some foreign "spy" (okay, it might happen if you happen to be doing something worth spying on) slip you a mickey, you'll be prepared and capable of handling yourself.