I have had 2 squib loads in my life....so far.
First one was when my father decided to come out and shoot with me once. He was firing my 1991A1 in 45ACP, and I caught the squib "sound" and started yelling for him to stop shooting. He pretty much gave up shooting after that, even though I made sure he knew that he was not to blame for the problem. No damage done, except that I think he never wanted to do that again.
The second time was with a AR that I was testing out for a friend. This one cost me a new upper to replace the one I wrecked. Gunsmith looked at everything on that deal and came to the conclusion that it was most likely an underloaded/underpowdered round that I had a detonation with.
BOTH were 100% my fault. No questions there. No excuses. I don't remember the 45 loading problem, just missed a powder charge is all. The 223, I knew what happened, and I was testing out Darwins theory on myself by not refilling my powder hopper when it was about empty.
Both could have been dangerous to myself/others. The AR did damage me, and I took off from reloading for almost a year after that happened.....it shook me pretty bad in the confidence department. I am back on the reloading wagon, and making much better decisions in the quality control department in my reloading steps.