Hitting himself is an extreme behavior. We are all, by nature, self preservers so hitting oneself is usually caused by some sort of outside interference. My questions would be:
When was his last vaccine?
Is your home detoxed? Most toxins take a few years to build up in a system so this age is when toxicity commonly shows itself in behavioral problems, respiratory problems, digestive issues, and the onset of "allergies."
Your husband's work raises a red flag for me as metal factories are full of issues. Your husband can be bringing things home on his clothes.
What is his food intake like? Is he taking an absorbable multivitamin to help his own system fight off all the things that we expose ourselves to?
These are just things to think about....