1. The Snell FAQ [below] appears to be mostly/totally a guess about the effects of "hair oils, body fluids and cosmetics, as well as normal "wear and tear"on helmet degradation. And no evidence of why/how 5 years was selected as a replacement date. If normal use degradation were true, would not replacement after one year or maybe six months be a more prudent recommendation for replacement for anyone seeking maximum protection from a safety device that degrades from normal use or even no use.

2. It does seem sensible to warn silly billys not to pour petroleum products all over a Styrofoam product.

3. The last reason furnished "experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five-year period due to advances in materials, designs, production methods and the standards" is laughable.

Extract from Snell FAQ:
Why should you replace your helmet every five years?

The five-year replacement recommendation is based on a consensus by both helmet manufacturers and the Snell Foundation. Glues, resins and other materials used in helmet production can affect liner materials. Hair oils, body fluids and cosmetics, as well as normal "wear and tear" all contribute to helmet degradation. Petroleum based products present in cleaners, paints, fuels and other commonly encountered materials may also degrade materials used in many helmets possibly degrading performance. Additionally, experience indicates there will be a noticeable improvement in the protective characteristic of helmets over a five-year period due to advances in materials, designs, production methods and the standards. Thus, the recommendation for five-year helmet replacement is a judgment call stemming from a prudent safety philosophy.