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Laser and Radiation Safety

Laser Safety

Fig: Damage caused to eyes (retina and cornea) and skin by high-power lasers.

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. A laser produces an intense, highly directional beam of light. High power lasers can cause damage to eyes and skin and in extreme cases cause blindness and burns (see Fig).

Exposure to Laser

  1. Primary beam: Direct hit/exposure from primary beam. This is the most hazardous.
  2. Specular reflection: Exposure from laser hitting a shiny/smooth surface. This can be as hazardous as the primary beam.
  3. Diffuse reflection: Exposure from a rough object. Typically, this is less serious but also hard to detect and hence dangerous.

Laser Classification

Lasers can be classified based on power and wavelength. For details please see
http://www.rli.com/resources/articles/classification.aspx
http://www.lasersafetyfacts.com/laserclasses.html

Visible lasers (400-700 nm)

Based on their hazard, laser sources are categorized into classes. Modern ANSI/IEC classification is preferred (See table below) over older FDA Roman numeral classification. (Class I-IV). Class 1 lasers have the lowest hazard while Class 4 lasers create the greatest hazard. Exposure is typically expected to be <0.25 s. It is expected that the user will have a aversion response, which will prevent longer exposures.

In general, we should never come in the way of laser light. Calculations have been done to estimate distance at which lasers with typical beam-spread are very dangerous. Calculations for some typical lasers are given in the table below. However, please remember that lasers are still dangerous beyond these distances. Do not stare at a laser, ever.

Non-Visible lasers (>700 nm)

Non-visible laser do not generate any aversion reflex. This significantly increases the possible of longer exposure which can be very dangerous. Even at lower powers there is a significant risk of losing eyesight.

The damage to the eye, depends on the laser wavelengths (see Fig below). Wavelengths between 380-1400 nm are transmitted by the cornea and absorbed in the retina. On the other hand, wavelengths longer than 1400 nm are strongly absorbed in the cornea and do not reach the retina for low exposures. Absorption in cornea also does damage, but since damage to retina is often irreparable, lasers from 380-1400 nm are considered more dangerous. Non-visible laser (700-1400 nm) are even more dangerous because there is no aversion response.

Fig: Effect of laser wavelength on various parts of the eyes. Retina damage is irreparable. Cornea and lens damage is extremely painful.

Laser Protection

Appropriate laser eye protection and other personal protective equipment must be worn while working around lasers, especially for Class III and IV lasers. The type of protective equipment will be based on the class and wavelength of the laser involved. Laser safety glasses have lens that reduce the intensity of an incident laser beam. Glasses are commonly rated based on transmittance, which is specified in terms of optical density (OD). Higher OD = higher level of protection. Select appropriate OD level based on the power level of the laser.

Unfortunately, the correct choice of laser safety eyewear depends upon many local factors other than power that cannot be evaluated remotely, including the beam path, laser parameters, and lab environment, we can’t recommend a specific eyewear for your application. Always, discuss your needs with your supervisor. Commonly used standards are the ANSI Z136 and EN 207 Standard.

Recommended tutorial: Click here

Best Practices

  1. Never look directly at the laser beam or light-pump source.
  2. Do not allow any object which could cause reflections in or along the beam, such as spherical buttons, screw heads, or jewelry, in the working area.
  3. Keep a high general illumination level where lasers are in operation to cause contraction of pupils and reduced hazard.
  4. Post warning signs on laser equipment and on the doors of labs/rooms that have laser equipment.
  5. Always wear personal protective glasses whenever lasers are in the same room, irrespective of whether you are using that laser or not.
Fig: Safety goggles with safety rating
  1. High-power lasers must be partitioned into separate work-spaces, with wall-to-floor partitions. No safety eyewear works for all wavelengths, so simultaneously using lasers with different wavelengths in the same work-area is dangerous.
  2. Good quality laser protection goggles often have relevant protection levels listed on them. Before using a laser equipment, always check if the protection is adequate.

Ultraviolet safety

  1. All radiation of wavelengths shorter than 350 nanometers should be considered dangerous.
  2. Protective safety glasses with UV absorbing lenses should be worn when there is even a chance of accidental eye exposure.
  3. Skin exposed to strong UV radiation can receive painful burns, analogous to sunburns. So be completely clothed while working with UV radiation.
  4. UV lights are often used to sterilize the room/area. In such cases please make sure the room had tinted/plastic windows, such that UV light does not escape.

X-Ray and Nuclear Safety

  1. Follow ALARA = As Low As Reasonably Achievable. This means reduce time, distance, and use shields to reduce your exposure to radiation.
  2. Laboratories with X-ray sources should have notices posted outside the door.
  3. According to GoI policy, all X-ray equipment must be registered with the AERB.
  4. All X-ray sources are expected to be shielded by safety enclosures so that no users are exposed to X-rays.
  5. Staff regularly working with X-rays must have thermoluminescent dosimeter (TLD), a type of radiation dosimeter that measured personal exposure.
  6. There should be automatic interlocks that shut off the sources when the safety enclosures are open.
  7. Disabling or dismantling the interlocks is expressly forbidden.
  8. AERB Directive No. 01/2011 lays down the maximum permissible exposure limits. These must be explicitly followed. The limits are different for operator (staff), trainees (students, post-docs, INUP) and general public (staff, admins, visitors, etc.).
  9. During pregnancy, maximum limits are even more stringent. Equivalent dose to embryo/fetus must be < 1 mSv
Fig: Maximum permissible exposure limits, as per AERB directive no. 01/2011
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