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Laser Classes And Hazards

The following is a summary of laser classification taken from ANSI Z136.1.

Laser Classes

Class 1 lasers

A Class 1 laser is considered to be incapable of producing damaging radiation levels and is therefore considered safe under normal working conditions. These lasers are exempt from most control measures. Many lasers in this class are lasers which are imbedded in an enclosure that prohibits or limits access to the laser radiation.

Class 2 lasers

Class 2 lasers are low power lasers that emit visible radiation, but do not exceed a power output of 1 mW. For this laser class, the normal human aversion response of (0.25 seconds) to bright radiant sources affords eye protection if the beam is viewed directly. The potential for eye hazard exists if this normal reflex motion is overcome and the exposure time is greater than 0.25 seconds.

Class 1M lasers

A Class 1M laser is considered to be incapable of producing hazardous exposure conditions during normal operation unless the beam is viewed with an optical instrument such as an eye-loupe or a telescope.

Class 2M lasers

A Class 2M laser emits visible radiation (400 to 700 nm) with a power output below 1 mW. Like Class 2 laser products, Class 2M lasers pose ocular hazards to the unaided eye, but are potentially hazardous when viewed with optical aids.

Class 3R lasers

Class 3R lasers are potentially hazardous under some direct and specular reflection viewing conditions, but the probability of an injury is small. Class 3R lasers do not pose either a fire hazard or diffuse-reflection hazard. The output power of a Class 3R laser is between 1 and 5 times the Class 1 power limit for wavelengths shorter than 400 nm (UV lasers) or longer than 700 nm or a output power of 5 mW for 400 nm to 700 nm wavelengths (visible lasers).

Class 3B lasers

Class 3B lasers are medium power lasers that have an output power of 5 mW – 500 mW. Viewing these lasers under direct beam and specular reflection conditions are hazardous. The diffuse reflection is usually not a hazard except for higher power Class 3B lasers. A Class 3B laser is not normally a fire hazard.

Class 4 lasers

Class 4 lasers are high power lasers with a power output above 500 mW. Exposure to the direct beam, specular reflections, or diffuse reflections presents a hazard to both the eye and skin. A Class 4 laser may be a fire hazard (radiant power > 2 W/cm2 is an ignition hazard). In addition, these lasers can create hazardous airborne contaminants and have a potentially lethal high voltage powersupply. Always enclose the entire laser beam path, if possible, or enclose most of the beam path to reduce the potential hazards.

Hazards

Improperly used laser devices are potentially dangerous. Effects can range from mild skin burns to irreversible injury to the skin and eye. The biological damage caused by lasers is produced through thermal, acoustical and photochemical processes.

Possible hazards according to laser classes are given in Table 14.2.

Thermal effects are caused by a rise in temperature following absorption of laser energy. The severity of the damage is dependent upon several factors, including exposure duration, wavelength of the beam, energy of the beam, and the area and type of tissue exposed to the beam.

Acoustical effects result from a mechanical shockwave, propagated through tissue, ultimately damaging the tissue. This happens when the laser beam causes localized vaporization of tissue, causing the shockwave analogous to ripples in water from throwing a rock into a pond.

Beam exposure may also cause photochemical effects when photons interact with tissue cells. A change in cell chemistry may result in damage or change to tissue. Photochemical effects depend greatly on wavelength. Table 14.3. summarizes the probable biological effects of exposure of eyes and skin to different wavelengths.

The visible and near infrared lasers have potential for retinal injury, Human cornea and lens are transparent to those wavelengths and laser light and energy can be focused by the lens onto the retina. The maximum absorption of laser energy onto the retina occurs in the range from 400 - 550 nm. Argon and YAG lasers operate in this range, making them the most hazardous lasers with respect to eye injuries. Lasers working under 550 nm wavelengths can cause a photochemical injury similar to sunburn. Photochemical effects are cumulative and result from long exposures (over 10 seconds) to diffuse or scattered light. Table 14.3 summarizes the most likely effects of overexposure to various commonly used lasers.

Table 14.2 TS-EN-60825-1 Laser classes and hazards

Class

Hazard

Warning statement

Class 1

Safe under reasonably foreseeable conditions

(NOTE: Class 1 lasers include high-power that are fully enclosed, such that potentially hazardous radiation is not accessible during use).

Class 1M

Safe for the naked eye, except if magnifying optics are used.

Do not stare directly with optical instruments.

Class 2

Safe for short exposures(less than 0.25s). The eye is protected by the blink reflex.

Do no stare into the beam.

Class 2M

Safe for shorts exposures(less than 0.25s). The eye is protected by the blink reflex except if magnifying optics are used.

Do not stare into beam or view directly with optical instruments.

Class 3R

Safe if handled with care, may be dangerous if mishandled. Risk is limited by the blink reflex and natural response to heating of cornea for infrared radiation.

Avoid direct eye exposure.

Class 3B

Direct viewing is hazardous. Protective eyewear necessary if the beam accessible. Safety interlocks are required to prevent access to hazardous laser radiation.

Class 4

Can burn the skin and cause permanent eye damage. Class 4 lasers can also present a fire hazard. Safety interlocks with manual reset are required to prevent access to hazardous laser radiation.

Avoid eye or skin exposure to direct or scattered radiation.

The warning statements accompany the title: ‘laser radiation’ and laser product type statement on laser product labels in the format:

LASER RADIATION

Warning statement

CLASS x LASER PRODUCT

Additional labelling may also be required dependent upon the laser class and beam accessibility

Thermal burns to the skin are rare. They usually require exposure to high energy beams for an extended period of time. Carbon dioxide and other infrared lasers are most commonly associated with thermal burns, since this wavelength range may penetrate deeply into skin tissue. The resulting burn may be first degree (reddening), second degree (blistering) or third degree (charring).

Some individuals are photosensitive or may be taking prescription drugs that induce photosensitivity. Particular attention must be given to the effect of these (prescribed) drugs, including some antibiotics and fungicides, on the individual taking the medication and working with or around lasers.

Table 14.3 Summary of laser biological effects

Photobiological Spectral Domain

Eye

Skin

Ultraviolet C (200 nm - 280 nm)

Photokeratitis

Erythema (sunburn)

Skin cancer

Accelerated skin aging

Ultraviolet B (280 nm - 315 nm)

Photokeratitis

Increased pigmentation

Ultraviolet A (315 nm - 400 nm)

Photochemical cataract

Pigment darkening

Skin burn

Visible (400 nm - 780 nm)

Photochemical and thermal retinal injury

Pigment darkening

Photosensitive reactions

Skin burn

Infrared A (780 nm - 1400 nm)

Cataract and retinal burn

Skin burn

Infrared B (1.4μm - 3.0 μm)

Corneal burn, aqueous flare, cataract

Skin burn

Infrared C (3.0 μm - 1000 mm)

Corneal burn only

Skin burn

Electrical hazards

  • The use of lasers or laser systems can present an electric shock hazard. This may occur from contact with exposed utility power utilization, device control, and power supply conductors operating at potentials of 50 Volts or more. These exposures can occur during laser set-up or installation, maintenance and service, where equipment protective covers are often removed to allow access to active components as required for those activities. The effect can range from a minor tingle to serious personal injury or death. Protection against accidental contact with energized conductors by means of a barrier system is the primary methodology to prevent electrical shock.
  • Another particular hazard is that high voltage electrical supplies and capacitors for lasers are often located close to cooling water pumps, lines, filters, etc. In the event of a spill or hose rupture, an extremely dangerous situation may take place. During times of high humidity, over-cooling can lead to condensation which can have similar effects.

Collateral and plasma radiation

Collateral radiation, i.e., radiation other than that associated with the primary laser beam, may be produced by system components such as power supplies, discharge lamps and plasma tubes. Such radiation may take the form of X-rays, UV, visible, infrared, microwave and radio-frequency radiation. “Home-built” lasers are again of particular concern and should be independently examined. In addition, when high power pulsed laser beams (peak irradiance of the order of 1012 Watts/cm2) are focused on a target, plasma is generated which may also emit collateral radiation. X-rays may be generated by electronic components of the laser system (e.g., high voltage vacuum tubes, usually greater than 15 kV) and from laser-metal induced plasmas.

Fire hazards

Class 4 laser systems represent a fire hazard. Enclosure of Class 3 laser beams can result in potential fire hazards if enclosure materials are likely to be exposed to irradiances exceeding 10 Watts/cm2. The use of flame retardant materials is encouraged.

Opaque laser barriers (e.g., curtains) can be used to block the laser beam from exiting the work area during certain operations (please see PPE Section and Appendix 14.1) While these barriers can be designed to offer a range of protection, they normally cannot withstand high irradiance levels for more than a few seconds without some damage, including the production of smoke, open fire, or penetration. Users of commercially available laser barriers should obtain appropriate fire prevention information from the manufacturer.

Operator of Class 4 lasers should be aware of the ability of unprotected wire insulation and plastic tubing to ignite from intense reflected or scattered beams, particularly from lasers operating at invisible wavelengths.

Compressed gases

Many hazardous gases are used in laser applications, including chlorine, fluorine, hydrogen chloride, and hydrogen fluoride. The use of mixtures with inert gases, rather than the pure gases is generally preferred. Hazardous gases should be stored in appropriately exhausted enclosures, with the gases permanently piped to the laser using the recommended metal tubing and fittings. An inert gas purge system and distinctive coloring of the pipes and fittings is also prudent.

Compressed gas cylinders should be secured from tipping. Other typical safety problems that arise when using compressed gases are:

  • working with free-standing cylinders not isolated from laboratory users
  • regulator disconnects, releasing contents to atmosphere
  • no remove shut-off valve or provisions for purging gas before disconnect or reconnect
  • labeled hazardous gas cylinders not maintained in appropriate exhausted enclosures
  • gases of different categories (toxics, corrosives, flammable, oxidizers, inerts, high pressure and cryogenics) not stored separately

Laser dyes

Laser dyes are complex fluorescent organic compounds which, when in solution with certain solvents, form a lasing medium for dye lasers. Certain dyes are highly toxic or carcinogenic. Since these dyes frequently need to be changed, special care must be taken when handling, preparing solutions, and operating dye lasers. The SDS for dye compounds should be available to and reviewed by all appropriate users.

The use of dimethylsulfoxide (DMSO) as a solvent for cyanide dyes in dye lasers should be discontinued, if possible. The DMSO aids in the transport of dyes into the skin. If another solvent cannot be found, low permeability gloves should be worn by users any time a situation arises where contact with the solvent may occur.

Preparation of dye solutions should be conducted in a fume hood. Personal protective equipment, such as lab coats, appropriate gloves, and eye protection are necessary when preparing solutions.

References and sources for information from the relevant websites and documentation of different universities, NGOs and government agencies used in the preparation of this website are provided at references.

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