Morning Carson,
Does the manufacturer have any information / advice regarding this?

I think you've highlighted a big issue in the goggles vs Light Eye Protection and impact resistance.
The reality is that most people assume LEP cannot withstand the same impact as goggles without even referring to markings. The only real difference in the standard is that goggles must remain in position following the impact.
If you have selected the correct impact resistance, as a rule of thumb lower for swarf, higher for grinding your then looking at how tight fitting you need for dust and debris, whether the face needs protecting, respiritory protection etc.

Regarding high energy impact from grinding in my experience it is high velocity and some reasonable size chunks can be generated particularly when dressing items.

BSEN 168 Personal Eye Protection - Non-Optical Test Methods appears to be relevant as well.

Sorry can't access it, the information provider my company uses refuses to open the document

I sympathise with carson's position - it's so easy to find in these situations that people use a certain item of PPE instead of another "because that's what they're always done".

A 6mm steel ball at 45m/sec would feel pretty darned high energy if it was aimed at me despite what BS EN 166 says!

The various manufacturers' and suppliers' sites often have excellent guidance on selection against standards, including for BS EN 166 - it's reasonable to go with these if there's nothing unusual about your activity. There's one at:

http://solutions.3m.co.u...ducts_for/EyeProtection/

Thanks everyone for your advice.

I still don't have an adequate means of determining what tasks produce low, medium and high energy particles. I guess we just go with the type of selector Gramsay has alluded to.

It would be better if tests were done on real life situations rather than a 6mm ball bearing scenario - that actually tells me nothing of value.

The 6mm ball does tell you something of value.

What is the mass of a 6mm steel ball?

From that you can estimate the energy of impact.

You can also use the 6mm size as a gauge as to the types/liklehood of debris/particles generated by your work activities.

Your original post said you weren't clear as to what constitutes high, medium and low impact.

As Jane points out, the Brirish Standard defines the velocities for low, medium and high impact.

If you take the information from Stihl saw about the blade speed - its probably a reasonable assumption that the initial velocity of the debris is the same as the tip speed of the blade.

You can then work out the impact energy from the previously given formula - hence determine what type of eye protection is required.

Alrernatively just assume everything is 'high' energy and go for eye protection of that standard. Thats the easy way out!

Its perfectly acceptable to make reasonable / justifiable assumptions when undertaking risk assessments, especially in QRA - quantified risk assessments.

Its done very often in risk assessments to justify engineering designs / ALARP arguments

Often recognised engineering science formula are used - as here.

The kinetic energy of an object is the energy which it possesses due to its motion.

http://en.wikipedia.org/wiki/Kinetic_energy

As the particle/object won't be approaching the speed of light, the formula E = 1/2 mv^2 is valid

If a particle/object is being accelerated from stationary up to a velocity of x m/s by virtue of it being cut away from its original structure - then it gains kinetic energy by the force applied to it i.e. from the blade of the saw.

What other mechanical energy is it gaining?

A small amount of Potential Energy as it falls to the ground along its trajectory PE = m x g x h

Although this is likely to be a relatively small amount of energy due to 'm' and 'h' being small, if at ground level.

You could resolve the impact force by the addition of vectors if you so desire.

I know everyone would normally say goggles for using stihl saws, but why?

Stihl saw rotates at approx 200mph (14-16 inch diameter blade). Any shards of metal / concrete could potentially be thrown into eye at this velocity. I think that is why.

It's not about not accepting the recognised standard, and I think that to present it as such is a gross misrepresentation of the question and debate.

The BS says that particular safety glasses are good for a particular energy impact of a particular impactor. It does NOT say they are good for impacts of that energy, and it does not have anything at all to say about assessing the energy of impacts. And that's even before getting to teh question of whetehr energy is an appropriate comparison anyway.

For example - the case has been cited of a stihl saw with 200mph tip speed. Does that require low or medium (or high) energy eye protection? And (critically) why? Routinely such an application would be labelled as requiring goggles with medium rating, but in reality the energy of the projectile is way, way below that of a low energy impact:

Low energy glasses resist a projectile with KE (as has been done to death in thread) of about 0.9J (6mm diameter sphere, 7850 kg/m3, 45 m/s).

Stihl saw cutting concrete, say it ejects a piece of fine aggregate, debris size 1mm diameter? density 2400 kg/m3, suppose the operative has their eye right up at the saw tip and the debris does not get slowed by air resistance in flight - that's a 0.005J impact, or about one two-hundredth of the energy for which 'low energy' glasses are tested.

Even if it's cutting steel and ejects a shard say 5mm x 1mm x 1mm, at 200 mph that's a 0.16J impact, or one sixth of a low energy impact.

I have never seen a credible basis for relating a particular industrial situation to an equivalence of the BS testing. I'm interested to see if anyone knows of such a thing, because while I've never seen one, that doesn't mean it doesn't exist.

The manufacturer recommendation cited in the thread starts from the point of saying 'do you want glasses for low or medium energy impact', which plainly does not help if that's the question you want answering.