European Standard · Eye Protection
EN 166 – Eye Protection: The Complete Guide to the European Personal Eye-Protection Standard
EN 166 is the core European standard that sets the general requirements, testing methods and marking rules for all personal eye-protection equipment used at work — safety spectacles, goggles and face shields. If a pair of safety glasses is sold as certified PPE in the EU, it has been tested against EN 166. This guide explains the scope, the marking codes stamped on the lens and frame (optical class, impact rating, field-of-use symbols), how to choose the right eye protection for a task, inspection and care, and the standards that sit alongside EN 166 in the eye-protection family.
1. Scope
EN 166 applies to all forms of personal eye protectors intended to protect the wearer against a range of hazards likely to be encountered in industrial, laboratory and other workplaces, including mechanical impact, dust, gas, liquid splash, molten metal and short-circuit electric arc. It defines the general build, robustness, optical quality, field-of-use and marking requirements that every certified eye protector must meet, regardless of the specific hazard it is designed for. EN 166 is normally read together with the hazard-specific filter standards (listed in section 2) that add extra requirements for optical radiation such as UV, IR, welding glare or sun glare.
2. Exclusions & Related Standards
EN 166 does not cover eyewear that falls under other dedicated standards. These related and referenced standards include:
- EN 167 – optical test methods used to verify EN 166 optical requirements
- EN 168 – non-optical test methods (robustness, resistance to ignition, corrosion)
- EN 169 – filters for welding and related techniques
- EN 170 – ultraviolet filters
- EN 171 – infrared filters
- EN 172 – sunglare filters for industrial use
- EN 175 – equipment for eye and face protection during welding
- EN 379 – automatic welding filters
- Prescription safety spectacles intended solely to correct eyesight without occupational protection claims
For head and hearing protection worn alongside eyewear, see EN 397 industrial safety helmets and EN 352 hearing protectors. For hand protection commonly used on the same tasks, see EN 388 protective gloves.
3. Marking System: Optical Class, Impact Rating & Field of Use
Every EN 166 lens and frame carries a set of stamped codes. Reading them correctly is essential for selecting the right protection.
Optical class (lens quality):
| Class 1 | Highest optical quality — suitable for continuous, full-shift wear |
| Class 2 | Medium optical quality — suitable for intermittent use |
| Class 3 | Lowest optical quality — short-term use only, not for prolonged wear |
Mechanical strength / impact resistance symbols:
| S | Increased robustness (resists a 22 m/s impact) |
| F | Low-energy impact (45 m/s) |
| B | Medium-energy impact (120 m/s) |
| A | High-energy impact (190 m/s) |
Field-of-use symbols (stamped on the frame):
| 3 | Liquid droplets and splashes |
| 4 | Large dust particles (>5 µm) |
| 5 | Gas and fine dust particles (<5 µm) |
| 8 | Short-circuit electric arc |
| 9 | Molten metal and hot solids |
Common additional markings: K – resistance to surface damage by fine particles (anti-scratch); N – resistance to fogging (anti-fog); R – increased reflectance in the infrared; H – frames designed to fit smaller head sizes; O – original (non-derived) resistance to ignition of surface material.
4. Requirements and Testing
- Optical quality: spherical/astigmatic power, prismatic deviation and light transmittance tested per EN 167
- Robustness: impact tests fire a steel ball at defined velocities (S / F / B / A) at the lens per EN 168
- Resistance to ignition of frame and lens materials
- Resistance to corrosion for metal parts
- Field-of-use performance: droplet, dust, gas and molten-metal resistance where the relevant symbol is claimed
- Resistance to fogging, tested and marked only where the “N” rating is claimed
- Manufacturer identification, CE marking and traceability information permanently marked on lens and frame
5. Selecting the Right Eye Protection
Match the field-of-use symbol and impact rating to the actual hazard: grinding and cutting call for at least an F or B rating with a 3/4/5 field-of-use symbol; chemical handling calls for goggles marked 3; electrical switchgear work calls for the 8 symbol; foundry and welding-adjacent tasks call for the 9 symbol. Eyewear should be compatible with other PPE worn at the same time, such as respirators, welding shields or hearing protectors, without creating gaps or pressure points. Where prescription correction is needed, use certified prescription safety eyewear rather than ordinary glasses under a face shield.
6. Inspection, Care and Maintenance
- Inspect lenses before each use for scratches, pitting, cracks or discolouration that reduce vision or strength
- Replace immediately if the lens is cracked, deeply scratched, or has taken a direct impact
- Clean with mild soap and water or a manufacturer-approved lens cleaner; abrasive cloths damage anti-scratch and anti-fog coatings
- Store in a case or pouch away from solvents, extreme heat and direct sunlight
- Check the elastic strap or arms regularly and replace when stretched or brittle
- Discard and replace eye protection at the end of its manufacturer-stated service life, even without visible damage
7. Product Examples
- Basic safety spectacles (Class 1, F-rated) for general workshop and warehouse use
- Wraparound safety goggles (3/4/5 field-of-use, N anti-fog) for chemical and dusty environments
- Impact-rated goggles (B or A rated) for grinding, chipping and machining
- Arc-rated face shields (8 symbol) for electrical switchgear and panel work
- Foundry face shields (9 symbol) for molten metal splash protection
- Over-spectacles designed to fit over prescription glasses
8. Standard Information
- Status: Active harmonised European standard
- ICS code: 13.340.20 – Eye and face protection
- Committee: CEN/TC 85 – Respiratory and eye protective devices
- Related standards: EN 397, EN 352, EN 388, EN 167, EN 168, EN 169–172, EN 175, EN 379
- Full standards library: Browse all EN standards
Frequently Asked Questions about EN 166
What does EN 166 cover?
EN 166 covers the general requirements, testing and marking of personal eye-protection equipment used against mechanical, chemical, dust, gas, molten-metal and electric-arc hazards at work.
What is the difference between optical Class 1, 2 and 3?
Class 1 is the highest optical quality and is suitable for continuous full-shift wear; Class 2 is suitable for intermittent use; Class 3 is the lowest quality and intended only for short-term use.
What do the S, F, B and A impact markings mean?
They indicate mechanical strength: S is increased robustness, F is low-energy impact, B is medium-energy impact, and A is high-energy impact, each tested at a defined ball velocity.
What do the field-of-use numbers 3, 4, 5, 8 and 9 mean?
3 means protection against liquid droplets, 4 means large dust particles, 5 means gas and fine dust, 8 means short-circuit electric arc, and 9 means molten metal and hot solids.
Can EN 166 safety glasses be worn over prescription glasses?
Only if they are specifically designed and certified as over-spectacles; otherwise certified prescription safety eyewear should be used instead of ordinary prescription glasses.
How often should safety glasses be replaced?
Replace immediately after any visible crack, deep scratch or direct impact, and otherwise follow the manufacturer's stated service life even if no damage is visible.
Is EN 166 the same as ANSI Z87.1?
No. EN 166 is the European standard while ANSI Z87.1 is the equivalent North American standard; they share similar goals but use different test methods and marking systems, so products certified to one are not automatically certified to the other.