Apologies but I don't quite understand what you mean by is it 'safe'?
Obviously they are made to be installed, if you mean are there any risks? Yes, but only if you do it carelessly.
- If you go in wearing lovely fluffy socks on carpet, you could generate static and discharge to your components, thus damaging them
- You could force the GPU in a way in which is damages the PCIe slot, the motherboard or the GPU itself
- You could get oil or dust on the major connections of the component
- You could forget to connect a key power connector or secure the GPU to the case
It's easier to damage the Motherboard, CPU etc.
But it really isn't difficult, there are risks associated with handling any electrical component, but with some very simple precautions, there will be no problem.