While bright candle has eluded to a good point about bio bb's shattering at a more common rate than non bio from various peoples anecdotal evidence it is worth pointing this out again while we are back at the "fragments in the eye" chestnut.
The energy carried by a bb is down to its mass and velocity. Velocity will not increase on impact it will decrease, its a law of physics due to energy being lost as heat, sound and in this case dispersed amongst the fragments). What this means it that there is minimal chance of a bb fragment making it through mesh into your eye and causing damage due to its impact with your eye, however there is a chance of damaging your eye by rubbing your eye with a fragment inside it. Which is why I carry a sterile eye wash as part of my mini first aid pack and use mesh goggles.
This is because I have tried numerous polycarbonate glasses and goggles and had fogging issues every time regardless of how I treat them. Which leads to this argument in my head, see well for a limited time and reduce an already minimal risk of fragments but risk crashing into or falling into things, OR deal with the slight loss of light and face the already mentioned minimal risk of fragments.
I think sites banning BioBB's is short sighted, probably because its easier to ban something if you don't understand it fully or as soon as you hear a horror story. We really need to start moving to more sustainable ammo, leaving thousands of little plastic balls everywhere is not environmentally sound.
Your eye pro is your choice and I leave that up to you however I choose mesh for the reasons I have outlined above.
If you decide you don't want to know the maths behind my decision then stop here. If you want the numbers I have shown my maths so read on.
So I shall use.
momentum (kg m/s) = mass (kg) x velocity (m/s)
followed by
force (N) = change in momentum kg m/s) / time (s)
Assuming the largest possible fragment of a bb that could penetrate the largest hole in a pair of mesh goggles with all of the velocity it had at the point of leaving the barrel (350fps or 106.68 m/s).
It would be a cylinder 6mm long the diameter of a bb and (if we take the largest holed mesh something like) 1mm radius (2mm diameter)
V= pi x radius squared x height = 3.14.... x (1x1) x 6 = 18.85 mm3
Volume of a 6mm bb = 113.1 mm3
Therefore assuming the person is using a .25 g bb as many of us are, its mass in kg would be 0.00025kg
Therefore the bb fragment would be , 0.00025kg x 18.85/113.1 = 0.0000416666 kg (ie 0.0416g that's less than 1/5th the mass of the bb)
So assuming the bb fragment that has been calculated above makes it through the mesh at the full speed the bb left the barrel of an airsoft gun.
Momentum (kg m/s) = 0.0000416666 x 106.68 = 0.0044449929 kg m/s
for the next part we have to assume the change in momentum is from the number above to 0 in 0 seconds ( an instant which it isn't because it will slow over a fraction of a second which I can't calculate without a seriously good high speed camera)
Force (N) = 0.0044449929 x 0 = 0.0044449929 N
I've only managed to find one reference (its a nature paper and for some reason I can't copy and paste the link) to the force required to penetrate an eye which relates to needles penetrating the back layer of an eye which raises some further points which I will go over later. The lowest "maximum force" in the journal paper was 0.19N which is far higher than the number above.
Needles have a much smaller surface area compared to the fragment in question so require much less force to penetrate anything this is shown in the same paper where the same type of needle as above required double the force if it pierces the rubber top of a vial. If I was to do this properly we ought to compare pressures but I really don't think many will have made it this far.
In conclusion, penetration injuries are unlikely with mesh eyepro unless they failed catastrophically (including shots ricocheting around the lenses) which is exactly the same way you would be injured from using polycarbonate lenses.
Well done for all those who made it this far through my meandering thought processes!
