Hi David,
Thanks for that.
After doing some more rooting around on it: the blind specifications refer to
compliance with standard 60825-4 on Laser Guards. The bias of that standard is towards
requirements for guards to fit around laser machining devices, based on the definition of
a "Protective Exposure Limit" (PEL) for guard materials. It looks like the PEL is just a statement of
the irradiance and duration for which a material can survive without letting anything greater
that Class 1 AEL exposures through the far side. e.g. can see some figures quoted for
PELs of about 250kW/m2 for 10s for lower resistance blinds. Back of the envelope suggests that's a sizeable
blast of laser: e.g. a 25W laser would need to be collimated to a 1cm2 beam (and stay steady for 10s)
to exceed that spec, so they seem to spec'd for fairly extreme conditions.
Think probably down (as usual) to a risk assessment, depending what's on far side of glass, distance to
laser etc., but my instinct is it may be over the top for normal conditions and as you suggest a
check on the ordinary fire retardant blind material may show it's fine for standard purposes.
Regards,
Gerard
-----Original Message-----
From: British Medical Laser Association [mailto:[log in to unmask]] On Behalf Of Taylor David (Clinical Scientist GRH)
Sent: 10 September 2015 14:10
To: [log in to unmask]
Subject: Re: laser blinds...
Gerard,
I would agree that your assessment of the function of window blinds (and I would include door aperture blinds too) is necessary and sufficient. It's easy to overlook the need to be fire-resistant, since the energy being stopped in an accidental strike could be considerable. Perhaps the fancy blinds have the equivalent of an 'L' number rating, rather than the 'OD' rating that we might assume for ordinary black-out blinds, and have higher resistance to physical damage under laser strike conditions. If any claim to that effect is made by the manufacturer, it could have an influence on the hazard assessment made for the controlled area, but a prolonged strike at a window blind is so unlikely that the assessment should take that into account.
If in doubt, you could deliberately strike the blinds with a laser beam (after checking what would be in line if the blind gives way) and see for yourself. I think I might be inclined to do the same even for a fancy 'laser-resistant' blind and see if it behaves any differently.
I should add that in all the years I spent as LPA, I never experienced any problems with window blinds, or more accurately, none was ever reported to me.
______________________________________________________________________
David Taylor, MA CPhys MInstP MIPEM - Consultant Medical Physicist ([log in to unmask]) (previously Head of Non-ionising Radiation Physics / Laser Protection Adviser) Medical Physics Department, Leadon House Gloucestershire Royal Hospital, Great Western Road GLOUCESTER, GL1 3NN, UK
Tel: +44 (0)300 422 5976
Fax: +44 (0)300 422 6489
Past Secretary/Treasurer - British Photodermatology Group (www.BPG.org.uk) ______________________________________________________________________
-----Original Message-----
From: British Medical Laser Association on behalf of Boyle, Gerard (MPBE)
Sent: Thu 10-Sep-15 13:44
To: [log in to unmask]
Subject: laser blinds...
On the subject of laser blinds (I know, it's a favourite!), what are views on 'special' laser proof blinds? Not talking about fancy glass ones, just the black-out, pull down type blinds for covering windows.
There are 'proper' laser proof blinds ones available, complete with standard and CE marking. But am wondering....what's wrong with just ordinary (and cheaper) fire proof blinds?
I'd see the function of blinds as stopping a brief and accidental reflection back into the room and blocking brief and accidental escape of the light from the room. Presumably ordinary and visibly opaque fire proof blinds are adequate for any imaginable scenario that could happen in a clinical set up? If someone is firing at a blind long enough to puncture a hole in, I'd imagine have a bigger problem than just blind construction...
Thoughts??
Regards,
Gerard
Principal Physicist,
Dept. of Medical Physics & Bioengineering, St. James's Hospital, Dublin.
01-4162769
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