In EN397, there is an area of 100mm diameter stipulated by the standard, and all impact and penetration tests are carried out within this circle. However, venture outside this 'magic circle' and the helmet doesn't need to conform to any standard. But imagine the site situation:
if something were to fall on your head, would it always fall directly onto the crown? What if you were looking down, and the object struck just 20mm outside the 'magic circle'. Play the following clip and you'll see the JSP mk7 helmet receive such a blow. Tough little shell, isn't it?!
