when is a helmet unsafe?

A quarter inch deep? That means the plastic shell is broken all the way through.

It's toast.

My rule is any impact that hurts.

If you feel that the helmet saved your coconut, it's time to retire it.  It paid for itself.

Quote:

Originally Posted by incognito 

 

If you feel that the helmet saved your coconut, it's time to retire it.  It paid for itself.

I thought you were supposed to wear them on your head... 

If you hit a tree hard enough to crack some ribs and dent your helmet it's time for a new helmt

Quote:

Originally Posted by bwana 

 

it didnt crack-just dented. the styrofoam inside is intact as well 

Only the side you can see.

For the side you can see (the inside): If you were to use the proper measuring tool, I guaranty you that your skull compressed the foam. you can't see it cause it is displaced over a large surface with your head.

Compromised the integrity.

Helmets are designed to absorb impact and displace energy, once the foam is compressed, the surrounding area of impact (molecules inside foam) are also compacted. The entire area around the impact zone is also compromised (reaction), along with the general structural stability and construction.

In other words; the SHOCK from impact that caused a dent, also caused vibration throughout the construction. Might look and feel normal, but next impact, helmet could explode. The impact foam will not properly absorb skull impact against object after any type of compression.

Toss it.

Don't sell it.

Toss it.

Yes, agree -- helmet are "single use" for impacts. 

"in general, how much damage can a helmet sustain before it has to be  tossed?"

When you have to ask this question it has sustained enough.

Meh, I'd wear it.  You see tons of people riding without helmets, yours at 80% is still way better than most.

$100 a fall would get really expensive to keep tossing helmets.