perkerk

Mythbusters demonstrated that their hammers, presumably high quality, defect-free hammers, don't chip or explode under normal and even excessive conditions. However, steel can contain impurities, or have problems during various annealing or tempering processes, that greatly increase the brittleness. The point of their experiment shouldn't have been to test whether quality hammers could be made to shatter, it should have been to pre-select known flawed/brittle hammers and test just how bad the shattering could be.

As is pointed out time and time again, why take the chance by testing your own hammer by banging it? Here's a recent event where steel shattered, and even certified safety glasses weren't enough to protect his eye:

http://machinedesign.com/article/inadequate-safety-glasses-no-miner-factor-in-injury-0810