I've lifted one in and out of a car boot a couple of times, usually on to sheets of cardboard. It's a very risky lift for your back as it is awkward and you'll have to stretch.
Yes incredibly risky at the point where you're lent over and the weight is away from the body. The effect of the weight upon the spine in this situation can cause serious damage.
I've suffered with bouts of crippling back pain on and off for most of my adult life from slipped discs and sciatica.
After the initial injury subsequent injuries occur frighteningly easy.
It's difficult to avoid completely when you do manual work, but I won't lift anything risky now, it's just not worth it.