From Title 21, Volume 8 of the Code of Federal Regulations.

Part 1040 — Performance Standards for Light-emitting Products

Sec. 1040.10 Laser Products

(http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=1040.10)

The following information will be used:

• Detailed descriptions of Class Levels
• Definitions (Collateral radiation, human access, integrated radiance, safety interlock, etc.)
• Federal regulations/guidelines for laser use/operation
• Several Cautions

J. Marshall, Br. J. Ophthalmol. 82, 1335 (1998).

• Why the eye is of primary interest in laser safety
  • The three primary damage mechanisms of over(eye)exposure to laser light
  • This is dependent on wavelength, pulse duration, and energy
• The history of laser safety and when codes of practice entered the laser realm
  • This began within 5 years of the first demonstration of a laser, 1960
• Definitions
  • Median Effective Dose (ED)
    • Dose which results in irreversible retinal damage
  • Maximum Permissible Exposure Levels (MPE)
    • Maximum exposure length that results in no damage
• Layman descriptions of laser classes
  • International concerns
    • World Health Organisation (WHO)
    • International Committee for Non-ionising Radiation Protection (ICNRP)
    • International Electro-technical Comission (IEC)
  • The development of laser pointers
    • Beginning with early laser pointers:
      • class 2 systems that used helium-neon laser sources with and emission wavelength at 632.8 nm
• Original intent of lasers for the public
  • For use in lecture theaters or boardrooms
• The visual effect of making eye-contact with laser light
  • In order of increasing brightness:
    • Dazzle
    • “After image” formation
    • Flash blindness
    • Irreversible damage

Dan Vergano. “Powerful laser pointers create risks: Lights deliver strong beams that can damage eyes.” USA TODAY 18 Nov. 2010

This article discusses the dangers of laser pointers sold via the internet. Points made are:

• These laser pointers contain greater strength than what is FDA approved, and the FDA only has jurisdiction over our producers and not our buyers
• Possible retinal damage (they cite the New England Journal of Medicine)
• Dangers of green colored laser pointers
• * this article is somewhat dramatized and contributes as a supporting element to the article by John Marshall

W. M. Steen and J. Mazumder, Laser Material Processing, 4th ed. (Springer, London, 2010).

• Chapter 13 of main interest
• Page 519 outlines main danger of lasers- damage to the eye, damage to the skin, electrical hazards, and fume hazards
• Danger to eye
  • Damage to retina in back of eye and damage to cornea in front
  • Radiation on retina focused by eye’s lens to amplify power by about 10^5 (100,000)
    • Laser at the visible or near-visible waveband are much more dangerous compared to outside the band
  • Eye damaged through explosive evaporation (cooking and boiling)
  • Safe exposure limit indicated by maximum permissible exposure (MPE) levels
    • Levels very low, especially as lasers become more powerful
• Danger to skin
  • Laser classes 3R, 3B, and 4 are dangerous to the skin, with 3R least dangerous and 4 most dangerous
  • Safety arrangements
    • 1) Beam terminated with material able to withstand beam for several minutes
    • 2) Stray reflections minimized
    • 3) All personnel must wear goggles
    • 4) Must seek approval for entry
    • 5) Warning lights and hazard notices
    • 6) Care taken in beam alignment
    • 7) Laser safety officer to check on guidelines
• Electrical danger
  • “A typical CO2 laser may have a power supply capable of firing the tubes with 30,000V with 400mA” (W. M. Steen and J. Mazumder 2010:525)
    • Fatal discharge possible at this level
  • Earthing system must be present
• Fume danger
  • High temperature of laser able to volatilise most materials, creating potentially dangerous fume
  • Organic materials particularly dangerous; laser might create radical groups highly dangerous to people

A. L. McKenzie, J. Radiol. Prot. 8, 209 (1988)

• “It would seem that no organ of the body is immune from incision, resection, coagulation or ablation by laser” (McKenzie 1988:209)
• Laser types and characteristics
  • Carbon dioxide laser
    • 20-100 W of far-infrared (wavelength of 10.6 μm)
    • Usually continuous, sometimes pulsed between several hundred and several thousand hertz
      • Radiation at this level easily absorbed in water- explosive disruption of cells as water becomes steam (tissue ablation by vaporisation)
    • Heat damage under the ablated surface is minimal
    • Because of tissue coagulation between 60-80 degrees Celsius, tissue is denatured and blood vessels are constricted; bloodless operation
      • Used in gynaecology procedures, especially treatment of cervical intra-epithelial neoplasia
  • Argon lasers
    • 3-6 W of blue-green light (usually several wavelengths at one time, usually 488 nm and 514.5 nm most common)
    • Highly scattered, diffuses a few hundred microns below tissue; good for surface use such as coagulation
  • Nd:YAG lasers
    • Neodymium-doped yttrium aluminium garnet
      • Nd:Y3Al5O12
    • Near-infrared radiation (wavelength of 1.06 μm)
      • Either continuous at 60-100 W or pulses at tens of nanoseconds at several mJ per pulse.
        • When pulsed, known as Q switched lasers as opposed to continously working (cw) mode
    • Beam scatters less than argon laser light, and absorbed less than carbon dioxide laser radiation
      • Can coagulate more volume (several mm of soft tissue) than both argon and carbon dioxide lasers
  • Other lasers
    • Krypton laser
      • 647 nm or 568 nm; can be tuned to any wavelength in visible spectrum
• Eye hazard
  • Sight impairment through retina, cornea, and/or lens damage
  • Cataract induced by absorption of near-infrared or ultraviolet radiation
    • Thermal damage present long before cataract, however
  • Cornea affected by heat like egg white- will “cook” the cornea and create opaque patch where laser impacts
  • Visible and near-infrared radiation at 1.06 μm can travel through ocular media to retina
    • ~ 40% of Nd:YAG laser radiation hits retina; ¾ will be transmitted or reflected (only ~10% absorbed in retina)
  • MPE
    • Carbon dioxide- 560 t^-0.75 mW cm^-2
    • Argon- 9 t^-0.25 mW cm^-2
    • Nd:YAG- 1.8 t^-0.25 mW cm^-2
    • Eye blink reflex time is usually cited as 0.25s
• Eye protection
  • Different types of eye protection are needed for different types of lasers in medicine
• Other hazards
  • Skin burns
    • Maximum permissible exposure tables are also calculated for skin contact, like for eye contact
    • Laser-proof protection is impractical to wear, however
      • Safety controlled by prevention of skin contact instead
  • Smoke
    • “Smoke is produced when cell water has been removed from soft tissue, leaving the dried framework to char and burn” (McKenzie 1988:217)
  • Fire
    • Cited by Fisher as a greater hazard than eye injury (McKenzie 1988:217)
• Laser theatre
  • Windows need to be shielded according to power of laser
• Laser Protection Adviser and Laser Protection Supervisor (LPA and LPS)
  • LPA in control of installation, training, and usage
  • LPS a subordinate of LPA; in charge of supervision and observation of the rules