UNDERSTANDING THE STANDARDS
When buying a helmet for clearing the woods, construction or other duties that come with maintaining what is yours, it is important to understand the ANSI Z89.1 standards. These go back nearly 25 years, and all helmets for professional construction types that were purchased after July 5, 1994, must comply with the performance guidelines in the ANSI Z89.1-1986 American National Standard for Personal Protection-protective Headwear for Industrial Workers Requirements.
There are also helmets designed for those who work with electric wires, and these could come in handy if you're running your own electrical grid. In this case, look for OSHA guidelines, including the Code of Federal Regulations (CFR) 1910.135 and 1926.100.
CFR 1910.135(a)(1) states, "Each affected employee shall wear protective helmets when working in areas where there is a potential for injury to the head from falling objects." That standard also addresses situations in which electrical hazards are present, because 1901.135(a)(2) requires that workers who perform tasks close to exposed electrical conductors should wear hard hats engineered to shield against shocks.
Helmets designed for the military must also meet key U.S. military standards; these include ballistic resistance and ballistic deformation. As of 2004, the military standards generally noted that the "ballistic hardware shall provide penetration resistance and shall not perforate or penetrate the witness plate against 9mm 124 grain FMJ projectile at 1400 +50/-0 fps."
In terms of ballistic deformation, the standards also noted, "When subjected to 9mm, 124 grain full metal jacket, projectile at 1400 (+ 50/–0) ft/sec at 0° obliquity at ambient conditions, the transient deformation of the shell shall not cause a deformation in the clay head form in excess of 1.0 inch."