The
TALSO [Triangle Area Laser Safety Officers] group met Thursday, November 13 at GSK's Building 5. Special thanks to Jyl Burgener and GlaxoSmithKline for hosting this event.
I. Welcome & Introduce new folks
- TALSO welcomes new member Allan Nowak of Dupont/RTP
II. Review notes from August 14 Meeting
- No action items from previous meeting
III. Case Study & Round Table Discussion: Hazard Evaluation of Laser
Cutting Operation (Waddell)
[How best to safeguard a laser cutting operation
involving both 1064 nm Nd:YAG
incident beam and intense broadband plasma radiation?]
- S. Waddell described 300W Nd:YAG aluminum tape cutting/welding device; work sits on
elevated platform with flat black Al shielding around it
- T. Hitchcock noted extensive
literature on Nd:YAG cutting/welding plasma at powers
<~450 W; articles generally indicate plasma radiation follows black body
radiation distribution, such that not much UVB & UVC produced. Total
Luminance & Blue Light hazards predominant
- Discussed possible shielding options,
e.g. curtained enclosures, tinted acrylic, etc. T. Hitchcock noted formulas in
literature for ensuring adequate optical density & threshold limits for
curtain/screen barriers at specified distance from plasma
IV. Technical Presentation: Free Electron Laser Beam Hazard Evaluation
(Edwards)
- B. Edwards gave brief overview of beam hazard characterization for Duke's
FEL.
- Question: how were Qf
& Qmpe calculated? Per Thomas et al (J.
Laser Appl. 13:4, 2001):
Qf [effective output power transmitted through
limiting aperture] = Qo[1-exp(-(Df/Dl)^2)] (for Gaussian
beam profile), where Qo is output energy per pulse, Df is limiting aperture, and Dl is beam diameter.
Qmpe [energy which, if transmitted through limiting
aperture, would result in MPE:H] = MPE:H*(pi*Df^2)/4
When MPEs involve different limiting apertures, the
MPE producing the highest Qf/Qmpe ratio determines
the applicable MPE, rather than simply the smallest MPE found by applying the
three repetitively pulsed laser "rules" in ANSI Z136.1-2000 section
8.2.3.
Note per Table 8 of ANSI Z136.1-2000, limiting aperture in UV region (0.18 um
to 0.4 um) and NIR (0.7 um to 1.4 um) varies depending on exposure duration.
In the example case presented during our meeting, for rules 1 & 3 the pulse
duration (50 ps) is used, giving a limiting aperture
of 0.1 cm, while for rule 2 the total exposure duration is used, yielding a
limiting aperture of 0.35 cm. As discussed, Thomas et al's "Qf/Qmpe ratio" is simply one way to ensure that the
effect of this limiting aperture difference is explicitly included in the
selection of the appropriate MPE; simply choosing the lowest MPE resulting from
the 3 rules would not take limiting aperture into account.
V. Any other business
- T. Hitchcock reported results from recent CLSO exam: 16/26 passed. LIA
plans to incorporate changes in LIA training to assist prospective CLSOs with the exam
- Congratulations to T. Hitchcock on his election to LIA Board!
- Duly noted: Presidential Commendation (from TALSO President Dan Sprau) for Jyl Burgener for hosting this meeting
VI. Schedule next meeting:
ACTION: BE investigate arranging for TALSO tour of Duke's FELL
List of potential discussion topics for upcoming meetings:
- Medical Surveillance (why,
whom & how much?)
- Tracking high power diode lasers
- Appropriate fire-proof materials
- Handling multiple wavelength lasers (e.g. Ti:Sapphire)
- Release of class 3b & 4 lasers into surplus & unrestricted use
- List of low-cost solutions to laser safety challenges & "low hanging
fruit" that get the most impact for the least resource expended in laser
safety programs
- Emerging issue: high power LEDs
- Harmonization of international LS standards
- LS for ultra-short pulsed laser systems
- Knowing the unknowable: how to assess US laser accident rates when no one
reports laser accidents
- Electrical Safety revisited
- Studying for the CLSO Exam: ideas and strategies
- Bring in a laser and demonstrate doing an alignment