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Dear Keewook Yi

The "laser rating" is the safety classification of the laser, broken
down into four major categories based on the risk posed to the user.
Below I've summarised the text from source URLs. Hope this helps.

Chris

In the US the categories are: (*)
Class I
Cannot emit laser radiation at known hazard levels (typically CW: 0.4
micro-watts at visible wavelengths).

Class II
Low power visible lasers which emit above Class I levels but emitting a
radiant power not above 1 mW. The concept is that the human aversion
reaction to bright light will protect a person.

Class IIA
A special designation that is based upon a 1000 second exposure and
applies only to lasers that are "not intended for viewing" such as a
supermarket laser scanner.

Class IIIA
Intermediate power lasers (CW: 1-5 mW). Only hazardous for intrabeam
viewing. Some limited controls are usually recommended.

Class IIIB
Moderate power lasers (CW: 5-500 mW, pulsed: 10 J/cm(2), or the diffuse
reflection limit, which ever is lower).

Class IV
High power lasers (cw: 500 mW) are hazardous to view under any
condition (directly or diffusely scattered) and are a potential fire
hazard and a skin hazard.

Embedded Laser
A Class II, Class III, or Class IV laser or laser system contained in a
protective housing and operated in a lower classification (Class I,
Class II or Class III).

In the UK the classifications are: (**)
I SAFE
Either (1) output is so low it is inherently safe; or (2) the laser is
part of a totally enclosed system.

II LOW POWER
Visible CW and pulsed lasers  In the case of CW (continuous wave)
lasers, eye protection is normally afforded by the natural aversion
responses. Hazard may be controlled by relatively simple procedures.

IIIA LOW - MEDIUM POWER
Extension of Class 2. Protection still afforded by natural aversion
responses, but direct intrabeam viewing with optical aids may be
hazardous. This must be controlled.

IIIB* LOW - MEDIUM POWER  As for Class 3A but there is a slight hazard
from viewing the direct beam. Power limited to 5mW. Visible only.

IIIB** MEDIUM POWER
Hazard from direct beam viewing and from specular reflections. More
detailed control measures are necessary.

IV HIGH POWER  Hazard from direct beam viewing, specular reflections
and diffuse reflections. Extreme caution required.

(*) http://www.admin.mtu.edu/fm/oshs/laser_safety/laser_classification/
(**) http://www.safety.ed.ac.uk/policy/part7_3/7.html

On Tuesday, May 20, 2003, at 04:26  pm, Yi, Keewook wrote:

> Dear confocal lovers,
>
> Does anyone tell me what means "laser rating"?
> Our safety manager wants to know what "laser rating" of our NORAN
> Odyssey confocal,
> because she needs to decide whether or not we should wear safety
> goggles
> during the work.
> She says it is like "2B" or "3B" something, but I could not find it in
> the manual.
>
> Thanks in advance.
>
>   Keewook Yi
--
Christopher F. Blanford
Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
Phone: +44 (0)1865 282603; Fax: +44 (0)1865 272690
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