We covered this topic a while ago and did some of our own tests. At the time, having done some worst case type testing, I meant to continue with some more realistic tests. I forgot. Well, now I have my Krinkov back, I did:
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So, somewhat counterintuitively, it took 17 BB's to get through the mesh at 1 inch, compared to the damage that 10 did at 2 feet, where just 1 more would have almost certainly penetrated. This result tends to lend weight to my theory that BB's lose considerable energy hitting each other.
At 1 inch there is so much less opportunity for the effects of minute differences of muzzle exit angle and air resistance to affect the trajectory, so the BB's will tend to hit each other closer to their centre of mass than when fired from further away, creating more compression of the BB plastic, absorbing more energy than when the impacts do not line up as well. Just like snooker, the further the impacting BB is from the centre of mass of the BB in front of it the more movement perpendicular to the direction of travel will result. It is this lateral movement which conserves more of the BB's energy as momentum than when some is lost as heat during compression.
So much for the elegance of BB physics, what we can determine regarding safety is that, at 1 inch range, for an average airsoft gun to blind somebody through this type of cheap mesh goggles, the trigger would have to be held down for approximately 1.7 seconds while the head and gun remain stationary relative to each other. I put it to you, ladies and gentlemen of the jury, that this is not merely highly unlikely but next to impossible, unless done deliberately to an unconscious or otherwise immobilised victim.
At the more realistic distance of 2 feet the danger is perhaps more alarming, since holding the trigger down for only 1.1s would probably penetrate the mesh, however it's worth bearing in mind that, to get this result, I did have to deliberately hold a steady aim. Again I find this highly unlikely.
We can also determine that not only would this type of mesh prevent injury in any likely skirmish or accidental discharge scenario, but also, despite that I expect we would all imagine ditching this type of goggles once dented to be a reasonable precaution, they would actually continue to protect against any likely impact at least once and possibly many more times, depending upon the number of individual BB hits.