These photos were taken several years ago in a nursing home. The conduit runs were above a lay-in ceiling. When they came down they broke water lines, gas lines, and the branch circuit and alarm / communications wiring. It was difficult working the scene with the lay in fixtures swinging from their whips, some still lit on the emergency circuit, with water on the floor.
Many years earlier some helper put up the conduit hangers with common nails, and the electrician snapped the pipe in place. I'm sure it looked right for inspection. Inspectors can't find hidden defects, but time does.
Fortunately no one was hurt.
(Notes with Images say that these were 3 runs of 4" EMT with 4 - 750 kcmil Alum in each. 100' long pulled loose from ceiling. Conduit was secured every 10' with Minneralac #9 held by a 3" nail. 2/93)
The more I see stuff like this the more I shudder. All to save time and a little money. Shoddy and disgusting. Do it right the first time. Someone is in big trouble and rightfully so. Im glad no one was hurt.
For structural engineering purposes, a 16D Common nail is rated for 141 lbs of pullout strength in nailing two 2xs together, and 165lbs in nailing 1/2" sheathing to 2xs, IIRC.
The wood looks OK in those photos, so I wouldn't suspect rotting or water. Vibrations or something else must have loosened them over time, causing them to fail. Either way, nails are the WRONG thing to use in that application, no question about it!
Yeah, I was originally thinking the same thing. A standard nail has nothing really for the wood to grip to. Even if I was going to use nails to hold something like this up (not likely though) I'd at least have the sense to use either an annular ring type or even a "Twist-Nail".