Laser Standards and Classification
Laser Safety falls under the ANSI 136.1
standard in the United States and the EN207/EN208/EC60825
standard in Europe.
Lasers are categorized by the ANSI Z136.1
standard into the following general categories. NOTE:
Category alone is not sufficient to determine if or
which eye protection is required.
| Class |
Definition |
Pulse
Length |
| 1 |
Non-hazardous |
Eyewear not required. |
| 1M |
Eye safe visible laser (400-700nm) if used without
magnifying optics. |
Eyewear not required unless used with magnifying
optics. |
| 2 |
Eye safe visible laser (400-700nm) (safe within
the blink reflex of 0.25s). |
Eyewear not required. |
| 2M |
Eye safe visible laser (400-700nm) (safe within
the blink reflex of 0.25s) if used without magnifying
optics. |
Eyewear recommended. |
| 3R |
Likely unsafe for intrabeam viewing. Maximum
Permissible Exposure (MPE) is up to 5 times class
2 limit for visible lasers of 5 times class 1
limit for invisible lasers. |
Eye hazard; eyewear is recommended. |
| 3B |
Eye hazardous for intrabeam viewing. Limited
diffuse hazard. |
Eye hazard; eyewear is recommended. |
| 4 |
Eye and skin hazard for direct and diffuse exposure.
Fire and burn hazard. |
Eye protection and other personal safety equipment
is required. |
ANSI Z136.1 requires specification of laser safety
eyewear according to optical densities (OD), and allows
a Nominal Hazard Zone (NHZ) to be calculated, outside
which diffuse viewing eyewear is allowed.
- Optical Density (OD) is a measure of the attenuation
of energy passing through a filter. The higher the
OD value, the higher the attenuation and the greater
the protection level. In other words, OD is a measure
of the laser energy that will pass through a filter.
- OD is the logarithmic reciprocal of transmittance,
expressed by the following: D? = -log10 T ?, where
T is transmittance.
| OD
(Optical Density) |
Transmission
in % |
Attenuation
Factor |
| 0 |
100% |
1 |
| 1 |
10% |
10 |
| 2 |
1% |
100 |
| 3 |
0.1% |
1,000 |
| 4 |
0.01% |
10,000 |
| 5 |
0.001% |
100,000 |
| 6 |
0.0001% |
1,000,000 |
| 7 |
0.00001% |
10,000,000 |
European Laser Safety Standards EN207/208/60825
European laser safety regulations EN 207/EN208 consider
Optical Density and also the power/energy density
(power over time over area) of the laser when determining
laser safety requirements. Like ANSI Z136.1, laser
safety eyewear must provide sufficient optical density
to reduce the power of a laser to be equal or less
than the Maximum Permissible Exposure levels (MPE),
but it must also provide damage threshold protection
(direct hit over a given amount of time/energy). Under
EN207, Laser safety goggles must protect against direct
intrabeam exposure to the laser.
The EN207 standard requires that eyewear is labeled
to with protection levels that detail their damage
thresholds, (e.g. 10600 D L5 (where L5 reflects a
power density of 100 MegaWatt/m2 during a 10 seconds
direct hit test at 10,600nm).
- EN207 L- ratings account for the damage threshold
of the eyewear material, i.e., the power density
eyewear will withstand, and requires actual laser
stability testing for at least 10 seconds (cw) or
100 pulses (pulsed modes).
Modes of Operation
Lasers operating at different modes
have different power density characteristics and often
different eyewear requirements.
| Mode |
Definition |
Pulse
Length |
| D |
Continuous Wave (cw) with consistent average
power |
greater than 0.25 second |
| I |
Pulsed: short single or periodic energy emission. |
> 1 µs to 0.25 s |
| R |
Giant Pulsed: very short single or periodic
energy emission. |
1 µs to 1 ns |
| M |
Mode Locked |
< 1 ns (pico and femtosecond) |