Bacteria can seep in through the pores of the egg, and it is so unreliable. Maybe it's somewhat safe, but it is not reliable at all. I used the float test on my first batch of chicken eggs that were on day 12. I couldn't tell anything by candling, and i was pretty inexperienced anyway. I did them all, and they all sunk. No movement, nothing. I was going to remove any duds and set new eggs, so I wanted to float test. I tossed them all. I took one out, and broke it open, and the little baby was alive. I couldn't do anything, I had to just watch it die. I'm sure a number of the other ones were alive too. So I will never use the float test again, even if it is "safe". It will only indicate the size of the air cell. More air = more buoyancy. Putting the egg in a gravity free environment makes it easier to see any movement. BUT... the chick may be resting... and not moving. So, if that's the case, the whole test is a waste of time. Not to mention: very porous eggs will absorb water through those pores, which may make an already too wet egg even wetter inside. And, if your humidity was too high or too low it will cause the egg to either ride lower in the water or totally float. Which will make the test results even more inaccurate. Candling is the only reliable method. If you can't see anything inside the egg, just leave it in. You can't change the results anyway, unless the chick is already internally or externally pipped. By then you could start assisting, but it might die from premature assisting too. Just leave them be for a little longer, and cross your fingers.
