EN 166 explained: markings, classes and what they mean day-to-day
Few standards are quoted as often as EN 166 — and few are as often misunderstood. We translate the key abbreviations into clear buying decisions.
Why EN 166 exists
EN 166 is the European base standard for personal eye protection. It defines the mechanical, optical and ergonomic requirements safety eyewear must meet to be sold as PPE (Category II).
Every certified model carries two markings: one on the lens and one on the temple or frame. They say different things — and both matter.
The lens marking — read left to right
Typical order: Filter code – Manufacturer – Optical class – Impact resistance – Additional symbols.
- Filter code (tinted/UV lenses only): e.g.
2C-1.2= UV filter with good colour recognition. - Manufacturer code: brand-specific, used for traceability.
- Optical class 1, 2 or 3 — see section below.
- Impact resistance:
S,F,BorA(6 mm steel ball at different speeds). - Additional symbols: e.g.
K(scratch-resistant),N(anti-fog),T(impact-tested at temperature extremes).
Optical class: the difference between half-day and all-day wear
- Class 1: highest optical quality, approved for continuous wear (8 hours+).
- Class 2: medium wear time, slight distortion allowed.
- Class 3: short use only — significant distortion possible; headaches and fatigue guaranteed with prolonged wear.
Rule of thumb: anything worn for more than an hour at a time should be Class 1.
Impact resistance: S – F – B – A
The letters mark the impact energy the eyewear withstands:
- S – increased robustness (static, 22 mm steel ball drop).
- F – 45 m/s (typical: grinding particles).
- B – 120 m/s (construction, metal forming).
- A – 190 m/s (fire service, high-energy industry).
A T right after the letter (FT, BT) means: also tested at –5 °C and +55 °C.
Often overlooked: the frame marking
The lens tells you what the lens can do. The frame marking tells you what the whole eyewear is approved for. If you find 3 (liquids), 4 (coarse dust), 5 (gas and fine dust) or 9 (molten metal) there, it applies to the complete protection. No marking on the frame — no approval, even if the lens could theoretically handle more.
What EN 166 does not cover
EN 166 is the base. Specific risks add further standards:
- EN 170 – UV filter
- EN 172 – solar protection for occupational use
- EN 169 / 175 / 379 – welding protection
- EN 207 / 208 – laser protection
Seeing only EN 166 at purchase means basic suitability was checked — nothing more, nothing less.
Frequently asked questions
- What does the number 1 on my safety glasses mean?
- The 1 directly after the manufacturer code is the highest optical class: the lens is approved for continuous wear of eight hours or more.
- Is EN 166 F enough for grinding work?
- Yes, F corresponds to 45 m/s particle speed and covers typical grinding and drilling. For construction and metal forming we recommend at least B (120 m/s).
- What does N mean on safety glasses?
- N stands for anti-fog per EN 168. The coating prevents condensation during temperature and humidity changes — essential for anyone wearing a mask.
- Can I use EN 166 safety glasses as sunglasses?
- Only if the lens also carries EN 172 (occupational solar) or EN 170 (UV filter). Without that marking, validated UV protection is missing.
Questions on this topic?
Our specialist partners advise you on site — from selection to individual fitting.
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