It's actually quite interesting to read all of these comments and see peoples thoughts on this topic. I'll give you the answer from a personal perspective, and also a perspective of someone who's been selling motorycle helmets for 8 years now.
I did notice someone said for a start Arai check the helmets over once crashed in, this has been a wierd rumour going round the motorcycle industry for years, Arai never scanned the helmets to check for damage, they'd simply turn around to you and tell you to buy a new helmet. once an impact has been taken All manufacturers will tell you this, I'm 100% certain of that.
As for the correct answer, yes you should change the helmet. There used to be an amazing video Nolan Helmets released a few years ago, where they held a helmet in a vice, and piled a led weight right into the forhead of the helmet, as some serious speed, and the first time this happened absolutely nothing happened to the helmet, no marks and you'd never notice the difference, however the second time they did the exact same weight, exact same speed it crumpled and the weight went straight through the shell and into the forehead of the person inside (obviously no one was wearing the helmet). This for me proved enough that once a helmet has taken an impact it shouldn't take a second at any time. I'm well aware people ride around in helmets they've dropped but trying to give someone proof of this is actually really difficult as everyone has their own opinion on the matter (just like everyone here has said conflicting things).
What I will say about the Go Pro is that it's actually going to make the impact worse, and "legally" you shouldn't have anything stuck onto the outside of your helmet. Now I know what you're all going to say, many of you have intercoms and cameras but the answer is technically you're all breaking the law
- A helmet is approved from the manufacturer as it comes in the box, once you put something onto it it would in theory need to be tested again to make sure it still passes the same test it passed without the addition of a go pro or intercom attached. It's a super grey area in the motorcycle industry and something you'll almost certainly never have heard anyone tell you before, and this is why helmet manufacturers are starting to make many helmets with comms as slick as possible integrated (Like the Shoei Neotec 2 with intercom ther's nothing sticking on the outside etc). As you can imagine these extra bits on the outside of a helmet make a very concentrated impact point, that if they were to take an impact on all the force gets focused on the same point in the helmet, which makes it much worse than something spread out. Imagine a dart tip, sharp it'll pierce through anything, vs a 2p coin it's spread out and won't pierce through everything. obviously this is n a bigger scale but I think you'll all understand my point here.
The other thing to note is, many manufacturers paint the inside of the polystyrene layer black so you're able to see how over time this cracks with wear and becomes "worn". This will give you a rough guide on how much white you can see coming through - there's no right or wrong when to change a helmet, but it's a bit of guidance as to when it'll be available.
Now the important part.. my personal opinion... Given my mass wealth of knowledge of how helmets are made would I personally change that helmet?
1. It would depend on how long I'd had the helmet, if it was up to 6 months old, I'd seriously struggle to reach back into my pocket again and spend another few hundred pounds on a helmet, so I think that would be partly swaying my decision. If it's a few years old then the answer would be yes I'd definitely change it anyways - it wouldn't be worth the risk for me personally.
2. How much is that helmet worth? If it's a big proportion of what "spare" cash you have then it may make it more difficult but for me I value my head, especially when the thing you're contemplating on could be the thing that means you walk away from an accident of not.
3.Was there an intercom / camera affecting how the impact was taken, if so yes that area of impact was concentrated so yes I'd be more leaning towards replacing.
4. How big was the impact? If it's a low roll then I probably wouldn't but if it was from waist height or above, and made a big "thud" then yes I'd replace the helmet.
I do hope this helps everyone's decision. This is a very well educated guidance and also my personal opinion involved as well. as always, anyone has any questions, I should after 8 years know pretty much everything you'd want to know so I'll do my best to help, but this subject is quite a grey area, with the correct answer being replace the helmet but there are other factors that come into place as well.