MZB calculation

[<Magnus Pihl>]

Dear Laserists,<P>I have a problem doing MZB calculations. I have learned two ways and they give totally different answers if it is safety or not. I think both make quite sense. Isn't there international regulations that are the same?<P>Please give your thought on these MZB calculations:<P>What I was told in Germany:<BR>---------------------------<BR>Total scan:6m<BR>Laser effect:0,25W<BR>Distance to laser:3,5m<P>At 3,5m the beam diametre is 7mm (at 1mrad).<BR>Laser power is then distributed at 0,007m*6m = 0,042m2. <BR>Pupil area: 3,85*10exp-5.<P>A perfect hit will make: (0,25W*3,85*10exp-5)/0,042m2 = 0,22mW<BR>10 seconds of exposure: (0,25*10)/0,042m2 = 59J/m2<BR>MZB at 10s exposure is 100J/m2 which is OK!<P>What I was told by Swedish authority:<BR>-------------------------------------<BR>Laser effect:0,005W<BR>Total scan:2m <BR>Scan frequency 50Hz<P>Will this work in 60 seconds, YES or NO:<P>Pupil area: <BR>(pi*diametre/2)= 3,85*10exp-5 m2<P>Pulse duration on the pupil (7mm):<BR>(7mm/scanwidth)*(1/scanfrequency)=<BR>(0,007m/2m)*(1/50Hz) = 70us<P>That makes the pulse-energydensity:<BR>(laserpower*pulseduration)/(eyearea)=<BR>(5mW*70us)/(3,85*10exp-5)= 9,09mJ/m2<P>MZB for a singlepulse:<BR>18*(70us)exp0,75=0,0138 J/m2<P>Number of pulses within 60 seconds: 50*60 = 3000<P>MZB for a single pulse in the pulsetrain:<BR>(3000exp-0,25)*0,0138 = 1,86mJ/m2<P>Answer: NO, it won't work, 9,09mJ/m2 is larger than 1,86mJ/m2

[ekkard]

Hi Magnus,<BR>sorry, obviously I did oversee your message.<BR>The international standard is the IEC 60825-1:Amendmend 2(2001-1). I will look after your calculations and take them as an example for my laser homepage. If ready I will tell you.

[ekkard]

Hi Magnus,<BR>the MZB calculations you gave are too poor to make decisions.<BR>The "German case" seems to be wrong:<BR>Someone forgot the repetition rate for scanned laser beams making up a "train of pulses".<BR>There is only the average power given, but you have to consider the worst of 3 cases<BR>- single pulse<BR>- average<BR>- train of pulses<BR>How did you limit the exposure time to 10 s?<BR>Time base is 100 s for non intentional intra beam viewing or 0.25 s for the case of accidential viewing or 30000 s (ca. 8 hrs) if you are looking intentional into the laser radiation, (or the total duration of the show).<BR>Which wavelength(s) (for the C3-factor)?<BR>100*C3 mJ/m^2 is only the "photochemical hazard" value. There is annother one for "thermal hazard" depending on the minimum viewing angle of the source, making up a C6-factor. For simplicity we can choose C6=1.<BR>You have to choose the worst case of both.<P>Can you provide more data (wavelengths, diameters of the apparent sources, scanning frequency, divergencies of the beams, mirror movement:rotating/swinging, what max. angles).

[ekkard]

Magnus Pihl hat mir noch einige Nüsse zum Knacken hinterlassen. Eine davon macht sich zunutze, dass bei Laserscannern (ins Publikum) das "reduzierte Einzelimpulskriterium" das kritischste ist. Dazu habe ich die Formel in einem üblichen Zeitbereich ein Bisschen modifiziert und mit Zahlen versehen. Wen's angeht und wen's interessiert: <A HREF="http://home.t-online.de/home/e.brewig/IEC2001test2.htm" TARGET=_blank>http://home.t-online.de/home/e.brewig/I ... st2.htm</A> <BR>(Bitte beachten, das ist ein S p e z i a l f a l l [img]images/icons/shocked.gif"%20border="0[/img] )<p>[ 08 October 2001: Message edited by: Ekkard ]