Which laser safety eyewear suits which laser?

This leads to a mistake that creeps in easily: eyewear already in the building, from a different application, gets used for the new machine because it is dark and lying in the cupboard. With a class 4 laser this can have serious consequences.

This article shows how to choose laser safety eyewear correctly: how to read the marking, which details about your machine you need and why the eyewear is always the last of several protective measures. What is binding is the risk assessment for your workplace.

Why dark eyewear is not yet protection

The link between tint and protective effect is weaker than appearances suggest. Safety eyewear filters particular wavelength ranges selectively — for other ranges it can be almost transparent without this being visible.

Cleaning lasers usually work in the near infrared at around 1064 nanometres. This radiation is invisible to the eye. There is no blink reflex to protect you and no perception that warns of exposure. Eyewear that darkens strongly in the visible range can be ineffective at 1064 nm.

Conversely, eyewear for 1064 nm is often surprisingly light. That is not a defect but intended: it blocks the infrared range and lets through enough of the visible range for the workpiece still to be assessed.

Which details about your machine you need

Four details come before the selection, all of which can be found in the operating instructions or on the rating plate:

• Wavelength in nanometres, usually 1064 nm on cleaning lasers
• Mode of operation: continuous wave or pulsed; on pulsed machines also the pulse duration
• Power or pulse energy
• Beam diameter or details of beam expansion

If one of these details is missing, a sound selection is not possible. The manufacturer should then be asked before ordering. A machine without reliable details of laser class and wavelength is a warning sign in any case.

Anyone operating several machines should lay the details side by side and record which pair of eyewear suits which machine. It is often possible to find one pair for several machines — but not always.

How the EN 207 marking is structured

Laser safety eyewear for occupational use is tested and marked to EN 207. The lens and the frame carry a combination of three details:

1. a letter for the mode of operation (continuous wave, pulsed, giant pulse, mode-locked)
2. the wavelength range in nanometres for which the test applies
3. the protection level, given as L followed by a number

A marking such as `D 1064 L5` therefore means: tested for continuous wave operation, at 1064 nanometres, protection level 5. If a different wavelength range appears there, the test does not apply to your machine.

It matters that lens and frame both have to be marked. A tested lens in an arbitrary frame does not make tested safety eyewear — the frame has to withstand the load as well.

What the protection level means

The protection level describes what power density the eyewear withstands for a defined exposure time without being penetrated. A higher number means a higher load capacity.

The appropriate level follows from the machine's characteristic values. It cannot be guessed, nor rounded up „to be on the safe side" without unnecessarily impairing vision. Manufacturers of safety eyewear offer selection aids for this; the basis is the data from your machine manufacturer and the risk assessment.

A higher protection level than required is no advantage. It darkens the field of view more, makes assessing the surface harder and tempts the wearer to take the eyewear off — at which point protection is gone entirely.

Why the mode of operation is part of the marking

A pulsed laser delivers the same average power to the material in very short, very energetic packets. For a protective filter that is a different load from a steady continuous wave.

That is why the mode of operation is part of the marking. Eyewear tested for continuous wave is not thereby suitable for pulsed operation — and vice versa. With cleaning lasers this is particularly relevant, because both pulsed and continuous wave machines are in use and both types often stand in the same workshop.

Anyone operating both a pulsed and a continuous wave machine needs either eyewear whose marking covers both modes, or two separate sets with an unambiguous assignment.

EN 208 alignment eyewear is something else

Alongside safety eyewear there is alignment eyewear to EN 208. It is intended for setting up: it attenuates the beam far enough for it to remain visible without causing immediate injury.

That is a different purpose and a different level of protection. Alignment eyewear does not replace safety eyewear for ongoing operation. Its marking begins with an R instead of an L — that is the quickest way to tell them apart.

For laser cleaning, alignment eyewear usually plays no role, because nothing is set up on a hand-held machine. Anyone who nevertheless has it on site should store and label both types clearly separately.

Visibility and residual light transmission

With laser cleaning the treated spot has to be assessed — otherwise it is impossible to tell whether the layer has been removed or the base material is already being attacked. Eyewear that lets through too little residual light makes that assessment hard.

Alongside the marking, therefore, pay attention to the stated luminous transmittance and, where possible, to colour rendering. Eyewear under which temper colours can no longer be told apart costs process quality.

Good workplace lighting helps as a complement. What is lost in brightness through the eyewear can be partly recovered there.

Fit, side protection and spectacle wearers

Stray radiation does not only come from the front. Safety eyewear without effective side protection lets radiation past at the edge — with class 4 also as a diffuse reflection from the workpiece.

For spectacle wearers there are two workable routes: overspecs worn over the corrective glasses, or safety eyewear with a built-in prescription. The second sits better and is worn more reliably in practice; it is, however, more expensive and has a delivery time.

The eyewear has to fit the wearer. Eyewear that pinches or slips gets taken off — and eyewear that has been taken off does not protect.

Ageing, damage and replacement

Protective filters age. Scratches, heat, solvents and simply time can change the filter effect without this being visible.

A simple rule in the workshop therefore makes sense: visual check before each use for scratches, cracks and deformation; replacement on visible damage; observance of the manufacturer's details on service life. Where safety eyewear is issued to several people, a simple record of who has which pair helps.

Damaged safety eyewear belongs in the waste, not in the spares cupboard.

Why the eyewear comes last

Personal protective equipment comes last in the hierarchy of protective measures. Technical measures come first — shielding, demarcation, interlocking — then organisational ones such as access rules and instruction, and only then the eyewear.

For a hand-held cleaning laser this means: the laser area has to be demarcated and marked, uninvolved persons have to be kept away, and extraction is part of the measures because particles and fumes are produced during ablation. The eyewear protects the person at the machine. It replaces none of these measures.

Anyone who only buys eyewear and leaves the rest open has not finished the risk assessment.

Typical mistakes when purchasing

Five points that regularly go wrong in practice:

1. Eyewear already in the building, from a different application, is reused without comparing the marking with the new machine.
2. Only one pair is purchased — for the person at the machine. Whoever stands next to them needs one too.
3. The mode of operation is overlooked: continuous wave marking on a pulsed machine.
4. The eyewear stays in the cupboard because it pinches. Fit is a safety question, not a comfort question.
5. Replacement is not regulated, so damaged eyewear stays in circulation.

None of these mistakes shows up in day-to-day operation. They show up once something has happened.

Sources

• EN 207 — Personal eye protection, filters and eye protectors against laser radiation — Marking from mode of operation, wavelength range and protection level; requirements for lens and frame.
• EN 208 — Eye protection for adjustment work on lasers — Distinction between alignment eyewear and laser safety eyewear for operation.
• OStrV — German regulation on the protection of workers from artificial optical radiation — Risk assessment, hierarchy of protective measures, provision of personal protective equipment.
• TROS Laser Radiation — Technical rules on the regulation — Assessment of the hazards and measures to protect employees.

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