My son is a human torpedo who tests the hardness of everything with his head. If he gets concussed (which has happened now twice), it's not a full day before he's head first into something again. His incidents have been unexpected backward falls. Self rabbit punching, I guess.
Fortunately, I checked this thing as it sits in the picture and I can't tip it even with my fatness (since it's thrown together, I have no clue how much it weighs - it's not that heavy, but it could be between 100 and 200 pounds).
My wife is safety police officer number one ("how are you sure that the orange stuff in the bottom of the fire pit isn't going to light the house on fire while we're sleeping?"), so the bed is actually a bit squat compared to most loft beds - just high enough for a mid height chest of drawers. This was not my choice, as my daughter's room isn't that large and it seemed like it would've been smart use of space if someone could've sat under it at a desk.
The kids will grow, though, until the sum of their weights is greater than mine and they will probably then tip it or manage to break a rail out.
My daughter has a normal sense of self preservation, but she's not afraid to beat her younger brother under the excuse of "he doesn't care if he gets hurt".