Safety Measures and control means to adopt during the setting up and the modify of laser and/or laser system are specified in CEI rule, file 1381G
"User's Guide for laser products for research laboratories".
This rule is completed to rule CEI 76-2, regarding the radiation safety of laser system.
Below are reported only some summerising notes in order to promptly enforce the rule to the specific cases present at INFN Padova Section.
Safety Procedure and Responsibility
While we are waiting to train specialized personnel for the function of Laser Technician with specific safety problems knowledge
(TSL) this role will be played by the head of the Protective and Preventive Service.
- The TSL advises safety rules and proper controls.
- The director, by the Experiment Head who uses the laser and/or the laser product,
is responsible of the taking over and of the setting-up of the necessary protective measures.
- The qualified worker directly involved are responsible for the use of laser system in compliance with the safety rules in force.
Lasers are classified in increasing risk classes :
· class 1 inherently safe laser during the normal working condition.
· class 2 laser which emits visible radiations in the interval of wavelenght between 400 and 700 nm.
The eye protection is normally assured by defence reactions, palpebral reflection inclusive.
· class 3A laser which are secure for a vision at naked eye.
For lasers which emit during the interval of weavelenght between 400 e 700 nm, the protection is assured by defence reactions,
palpebral reflection inclusive. For the other wavelenghts the risk for the naked eye is not greater than those of
Class 1. The direct vision of lasers beam of Class 3A with optical instruments (i.e. . binocs, telescope, microscope) would present an hazard.
· class 3B the direct vision of the beam of these
lasers is always dangerous. The vision of specular reflection is normally dangerous.
· class 4 lasers which can produce dangerous diffused reflection,
can cause skin injury and could also cause fire hazard.
Their use requires extremely care/attention.
The builder and his agent are responsible for furnishing the correct classification of a laser system.
If an already classified laser product is modified by the users influecing any aspects of the performances of the instrument
or of its functions, the person or the organization who makes this modify has the responsability to assure the reclassification
and the relabbeling of the laser system.
Compulsory Safety Measures for lasers of class 3B and 4
Protective screens must be used where possible. The screens must be furnished of relevant warning signs on removable parts or nearness the service connection indicating the risk owing to possible clearance or disconnectedness.
When there are not protective screens and, anyway every time , it is appropriate to value the opportunity of:
· locating restriction of accesses
· protecting eyes
· carrying out controls on the area
· putting barriers or attenuators
· imposing proper rules of procedures
· setting up an instruction and training program for the users
Further to the above mentioned it is compulsory to :
· Use of the remote interlock connector: connected to an emergency interlock switch of central
emergency and placed near the area where the sperimental activity is conducted.
Could be substituted by a safety interlock of the room, of the door or of casings.
· Key control: when not working any system must be protected against
any non authorized use from the removal of the key control.
· Beam stop or beam attenuator: the attenuator, if possible,
must be used to avoid the unintentional exposure to laser radiation of present people. An attenuator
or a beam stop must anyway be connected to the laser system permanently to avoid the exit of radiation when the system is in stand by .
· Warning sign:must be as the regulation in force and be
exposed at the entrance of areas or environments containing laser systems
· Control of beams way: the beam emitted from any laser
system should end , when not use, on attenuators or adeguate absorbers The ways of the beams
in free propagation must be anyway situated at a certain level to avoid that workers, during
their movement can be run into the eyes. The laser beams must be contained when possible.
· Eliminations of specular reflections:precautions must be taken to
avoid the unintentional specular reflection of the emitted radiations.
· Eyes protection: an ocular protector must be choosen
considering at least the wavelenght, the energetic exposition and the confort (for instance
the necessity of utilizing also corrective lens) . On each ocular protector must be clearly
indicated the right information to assure the correct use. The use of reflecting surfaces must be avoid.
· Protection clothing: if necessary, proper protection clothings
must be dressed in order to protect skin from laser radiation. Clothings must be of proper material to avoid fire risk.
People designed to use drive or laser products moreover of class 3B o 4, must have a proper training.
This training must be concerned with the following :
· to get used to the system working procedure.
· the use of proper control procedure of danger, of warning.
· the need of individual protection.
· the procedures of incident report.
· the byological effects of the laser on the eye and on the skin .
Before using a laser or a laser system, especially of class 3B o 4, all necessary information must be given to the doctors in order to value the necessity of health surveillance.
Risks that may occur when laser is working
The following risks must be considered depending on the type of laser used.
· Atmosphere contamination: gas orsteam originating from laser
system gas circulation , or by intermediate products of laser reactions, gas or steam from cryogenic agent.
· Ultraviolet radiation , visible or infrared: own to flash lamps, discharge
tube, pumping sources or feed-back radiations.
· Electric danger: owning to use of high tension and energy kept in bench of condensers of pulsed lasers.
· Cryogenic agent: risks owing to use and the manipulation of cryogenic liquids
· Fire or burning risks: this risk could persists also at a large distance from the
laser system for the interaction of the beam with inflammable substances.
· Explosions: there is the possibility of explosions in the bench of
condensers or in the optical pumping system so as of explosive reaction of reagents in the chemical lasers
or of other lasers used in laboratory.
Specific prescription for each laser classes
· class 2
A very temporary ocular exposure is not considered dangerous , still, the laser beam must not be directed on purpose to people
· class 3A
The use of optical instruments (binoculars , etc.) could be dangerous and must be carefully estimated. Moreover :
a) in the areas of use an information sign must be sticked
b)In order to facilitate the alignment of laser and of its connection with the system use mechanical or electronic means.
c) the beam must be , if possible , stopped at the end of its way.
d) The beam way must be situated , if possible, very far over or down to the eyes.
e) Must be taken the necessary precautions to avoid the laser beam is direct ,without intention, on reflecting surfaces.
f) Must be taken the necessary precautions in order that non authorized people use laser system,
· class 3B
Must be observed the foreseen precautions for class 3A and moreover :
a) the laser working must occur in one controlled zone by operators.
b) the specular reflections must be avoided.
c) the laser beam must be limited at the end by a body formed by radiating matter of color and reflectivity
d) if necessary , appropriate glasses must be wear
e) in the areas of use must be fixed a sing of laser warning
· class 4
Must be observed the foreseen precautions for the class e3B and moreover:
a) the beams ways should be protected whenever it is possible. Admittance nearby laser during its working is limited to
technical people who wear appropriate ocular antilaser protections and protective clothes.
b) whenever it is possible remote controls must be used
c) if the eye is protected, the environment lighting must however be enough
d) fire is a potential danger if associated to lasers of great power. To stop beams, suitable material must be choosen.
e) Special precautions must be taken to prevent undesired reflections, the beam and the area of collision must be covered with opaque
matter by laserwavelenght.
The potential for injury to the different structures of the eye
depend upon which structure absorbs the energy. Laser radiation may damage the cornea,
lens or retina depending on the wavelength, intensity of the radiation
and the absorption characteristics of different eye tissues.
Wavelengths between 400 nm and 1400 nm are transmitted through
the curved cornea and lens and focused on the retina. Intra beam viewing of a point source of light
produces a very small spot on the retina resulting in a greatly increased power density and an increase chance of damage.
A large source of light such as a diffuse reflection of a laser beam produces light that enters the eye at
a large angle is called an extended source. An extended source produces a relatively large image on the retina
and energy is not concentrated on a small area the retina as in a point source.
Details of Irradiation Effects on Eyes
Ultraviolet-B+C (100 - 315 nm)
The surface of the cornea absorbs all UV of these wavelengths (Figure 10) which produce a photokeratitis (welders flash) by a photochemical process which cause a denaturation of proteins in the cornea . This is a temporary condition because the corneal tissues regenerate very quickly.
Ultraviolet -A ( 315 - 400 nm)
The cornea, lens and aqueous humour allow Ultraviolet radiation of these wavelengths (Figure 12) and the principal absorber is the lens. Photochemical processes denature proteins in the lens resulting in the formation of cataracts.
Visible light and Infrared-A (400 - 1400 nm)
The cornea, lens and vitreous fluid are transparent to electromagnetic radiation of these wavelengths (Figure 11). Damage to the retinal tissue occurs by absorption of light and its conversion to heat by the melanin granules in the pigmented epithelium or by photochemical action to the photoreceptor. The focusing effects of the cornea and lens will increase the irradiance on the retina by up to 100,000 times. For visible light 400 to 700 nm the aversion reflex which takes 0.25 seconds may reduce exposure causing the subject to turn away from a bright light source. However this will not occur if the intensity of the laser is great enough to produce damage in less than 0.25 sec. or when light of 700 - 1400 nm (near infrared) is used as the human eye is insensitive to these wavelengths.
Infrared-B and Infrared-C (1400 to 1.0 x 10+6 nm)
Corneal tissue will absorb light with a wavelength longer than 1400 nm (Figure 10). Damage to the cornea results from the absorption of energy by tears and tissue water causing a temperature rise and subsequent denaturation of protein in the corneal surface. Wavelengths from 1400 to 3000 nm penetrate deeper and may lead to the development of cataracts resulting from the heating of proteins in the lens. The critical temperature for damage is not much above normal body temperature.
Laser Radiation Effects on Skin
Skin effects are generally considered of secondary importance except for high power infra red lasers.
However with the increased use of lasers emitting in the ultraviolet spectral region, skin effects have assumed greater importance.
Erythema (sunburn), skin cancer and accelerated skin aging are produced by emissions in the 200 to 280 nm range.
Increased pigmentation results from exposure to light with wavelengths of 280 to 400 nm.
Photosensitization has resulted from the skin being exposed to light from 310 to 700 nm.
Lasers emitting radiation in the visible and infrared regions produce effects that vary from a mild reddening to blisters and charring.
These conditions are usually repairable or reversible however depigmentation, ulceration, and scarring of the skin,
and damage to underlying organs may occur from extremely high powered lasers.
Summary of Wavelengths of Light and their Effects on Tissues
Below is a summary of interaction of optical radiation and various tissues. The wavelengths are divided into bands as defied by the International Commission on Illumination (CIE).