Congratulations! Any bike accident that you walk away from was a good one. I had one that I definitely did not walk away from and it's been a real joy to this day, every day.

Can you describe what happened? Always interested in learning from other cyclists what to watch out for.

It's often not clear whether the energy went into the helmet. It could have cracked something internally or substantially weakened the EPS under the plastic shell without it being super visible.

Better to not risk it: serious crash, replace helmet.

> If the helmet wasn't damaged in the crash it meant the energy was harmlessly transferred into your head.

Foam can and does distribute and absorb shock without being significantly damaged or destroyed in less severe collisions, crashes that can still put you in the hospital without a helmet.

I would maybe describe how helmets work as having a shock-absorbing cushion that slows deceleration of it’s contents. Talking about “energy” is bound to be misleading or confusing, since from a given speed, you always transfer the same amount of energy no matter how you stop, whether it’s a sudden strike against concrete or a slow gentle braking, or even waiting several minutes for air and tire friction to wear out all your kinetic energy.

I don’t want the helmet to be damaged or destroyed only because that means the crash is bad or severe.

There's much in this thread about the helmet absorbing the energy of the impact, but that's far from the whole benefit of wearing one.

The helmet, by conforming to the shape of your head, distributes the energy from the point of impact to a much larger area. So instead of having your head cracked open at the point it hits the tarmac, or pierced by a pointy rock, the force will be evenly distributed across your head.

The helmet also has a low-friction shell that will slide across a surface, which helps avoid head rotation, snapping your neck or getting whiplash, and will protect you from cuts and abrasions.

I've been saved by my helmet many times.

If you didn't know better, it looked like someone hit the helmet with a hammer a couple of times.

So yes, some amount of kinetic energy was dissipated in deformation of the plastic rather than my skull. I was more than a little grateful.

When I was a kid, I put an egg in a container of honey and dropped it from a 2nd-story balcony onto a hard surface. The egg remained unbroken. The honey was undamaged.

The kinetic energy represented by the difference in height was still added to the egg, but the honey slowed the transfer down, and spread it out to the whole object, in the same way that walking the egg down the stairs, instead of dropping it off the balcony, would have slowed it down.

You don't always want the helmet to be damaged. I wouldn't want my helmet to be constantly denting, cracking, spalling, and ablating every time it touched something. You really want it to be damaged only when the kinetic energy is coming in too quickly to safely (slowly, widely) transfer it all to the protected head, and permanent deformation is the fastest way to bleed off that excess. In theory, the helmet could also heat up when it gets hit, but that's more expensive than just wrapping EPS around whatever you want to protect.