Enh, shocks are designed to bottom out occaisionally and it shouldn't hurt anything. There's no set height or equation for what will damage a shock, and it's much harder to blow out an oil/coil shock than it is an air shock. I wouldn't worry about it. Norco's are tough bikes designed for all sorts of insanity. Thrash on it as much as you like and don't let the bike hold you back.