How long do helmets last?

geardad said:

in terms of exposure of the styrofoam to the air; I know lots of materials degrade merely by exposure to air.

also, what level of cracking or breaking is acceptable? IOW, are there some cracks which do not diminish the styrofoam's ability to absorb impact so that your noggin doesn't have to?

thanks!

gd

ANSI states that a helmet is only good for 5 years before the styrofoam has degraded to the point where it will not provide adequate impact protection. This is for a helmet that had never been involved in a crash. Any helmet that has been worn during a crash should be replaced, even if it appears that there has been no damage. If there are cracks in the styrofoam, the helmet should be replaced. In helmet design, there is no such thing as cracks that do not diminish the styrofoam's ability to absorb an impact.

Oi it's not just exposure to air ! also UV radiation will always make things brittle, over time...I wonder whether sweat also has an effect on plastic/styrofoam?

As with all other saftey parameters, i would expect 5 years to be teetering on the side of caution - i.e. a conservative estimate.