Bike Helmets - Lifespan??

Price has nothing to do with safety in terms of helmets.  They all have to go through the same safety standards. 

Yes, they are a one and done proposition in terms of accidents.   

Not sure about longevity. 

I've heard pretty much the same--after 2-3 years or one decent impact you should replace the helmet.  Seems a little conservative to me, but helmets are cheap and my head is fairly important to me. 

The expensive helmets are not necessarily any safer.  All helmets have to pass the same tests for certification.  More money gets you fancier designs, closure systems, etc.

For motorcycle helmets it was

• Replace when the new Snell or DOT rating comes out (about every 5 yrs)
• Replace after an accident.
• Send back to manufacture for inspection if dropped.

I found this list for bike helmets that seems realistic:

http://www.helmets.org/replace.htm

Helmets are designed to absorb the impact force by compressing the foam.  Once this happens it does not recover.  If you drop it on the floor, you may crack the foam.  In an accident it will break rather than compress leaving you no protection. 

I agree that the helmet is good for one impact, but I'm not so sure about that including dropping it on the floor. It's the crushing of the foam that is the protection to your noggin (a less severe deceleration, lessening the impact of the brain on the skull). Dropping the helmet (unless there's a bowling ball inside it) doesn't crush the foam.

But there is a lifespan. I've read 3 years if you ride outside with any regularity, and less if you ride a lot. The way I heard it, though, was that it was the UV light that caused the slow degradation of the foam, not sweat.