Laser Radiation Hazards & Control 2007 PDF

National Environment Agency Radiation Protection & Nuclear Science Department Laser Radiation Hazards & Control  2007 by Dr Phua Tan Tee Laser Radiation Hazards & Control...

National Environment Agency Radiation Protection & Nuclear Science Department Laser Radiation Hazards & Control  2007 by Dr Phua Tan Tee Laser Radiation Hazards & Control Contents 1 Ionising radiation and Non-Ionising radiation 2 Laser Radiation a Physical Characteristics b Laser Sources c Classification of Laser d Laser Applications i Industrial ii Medical iii Research e Laser Radiation Hazards and its Exposure Limits Ocular exposure to Laser Radiation Skin Exposure to Laser Radiation Exposure Limits f Safety guides against laser Radiation 3 The Radiation Protection Act 2007 4 Radiation Protection (Non-Ionising Radiation) Regulations 1991 a Ultraviolet sunlamps b Microwave ovens c Medical and Industrial Ultrasound Apparatus d Magnetic Resonance Imaging (MRI) apparatus e Entertainment Lasers f High Power Lasers 1 g Various Types of NIR Licences Issued by RPNSD 2 1 Ionising Radiation and Non-Ionising Radiation Ionisation is an electrical process in which an electron is knocked out of its orbit. Ionising radiation is radiation that is energetic and capable of causing atoms and molecules in its path to split into positive and negative ions. Ionising radiation include alpha, beta and gamma rays that are arisen by the decay of radioactive substances and X-ray that is produced electronically by X-ray machines. Alpha and beta are particulate radiation while gamma and X-rays are electromagnetic radiation of wavelengths from 100 nm to 10 - 5 nm. Alpha, beta & gamma rays are resulted from spontaneous re-- arrangements within unstable nuclei but X-rays are produced by electrons jumping between orbits close to the nucleus or by electrons losing energy when passing through the strong electric field close to the nucleus. Unlike the radiation from radioactive sources, the X-rays can at anytime be "turned off" by merely disconnecting the high voltage. Alpha and beta are sub-atomic particles while gamma and X-rays are electromagnetic rays similar to light. These radiation differ in their penetration abilities as follows:- * Alpha radiation can be completely absorbed by a sheet of paper or a few centimetres of air, * Beta radiation can be completely absorbed by a few cms of wood, glass, water or several meters of air, * Gamma & X-ray radiation are difficult to be absorbed completely, but the intensity can be reduced significantly by a few mms of lead, or a few cms of concrete or brick, for low energy radiation and by 10 or more cms of lead or a meter or so of concrete or brick for high energy radiation. Non-ionising radiation refer to the radiation that the energy is not capable in causing ionisation but is capable in causing other injuries to the body. It includes the electromagnetic radiation and fields with wavelengths greater than 100 nm and acoustic radiation and fields with frequencies above 16 kHz. Examples are microwave, ultraviolet, visible, infrared, laser and ultrasound radiation. 3 Non-ionising Radiation Ionising Radiation wavelength m 10 10 10 7 10 3 0.75 0.4 0.04 10 - 8 RF microwave infrared visible ultraviolet X & gamma Electromagnetic radiation is created by oscillating electric charges. The frequency of oscillation determines the kind of radiation that is emitted. Electromagnetic radiation can be considered as a stream of particles called photons. Each photon has associated with it an amount of energy hv, where h is Planck's constant (6.626 x 10 - 34 Joule.sec or 4.1357 x 10 - 15 eV. sec). The frequency of the wave motion can be used to calculate the energy of the emitted photon; thus, radiation has a dual wave-particle character. Type of Frequency Photon Regio Radiation Waveleng Energy n th Ionising Ray Gamma > 10 19 Hz < 0.03 nm > 40 keV rays Radiatio Regio n n 3 x 10 15 Hz 0.03 nm 12.4 eV X-rays to to to 10 19 Hz 100 nm 40 keV 7.5 x 10 14 Hz 100 nm 3.1 eV Ultraviolet to to to Non- 1.67 x 10 15 400 nm 6.9 eV Ionising Optica Hz l Radiatio n Regio n 4.3 x 10 14 Hz 400 nm 1.77 eV 4  Visible to to to 7.5 x 10 14 Hz 700 nm 3.1 eV 3 x 10 11 Hz 700 nm 0.00124 Infrared to to eV 4.3 x 10 14 Hz 1 mm to 1.77 eV Wave 300 MHz 1 mm 10 - 6 eV Microwave to to to Regio 300 GHz 1m 10 - 3 eV n Radiowave < 300 MHz >1m < 10 - 6 eV The biological effects due to the non-ionising electromagnetic Radiation is very different from the effects due to the X-rays and gamma radiation. The effect mainly is the thermal effect and it has no cumulative effect. However, with sufficient energy, the non-ionising radiation can cause injuries to the human body. For example, high power lasers can produce skin burn and eye injury, over exposure to ultraviolet radiation can cause skin cancer, exposure to extremely high intensity ultrasound can elevate the tissue temperature and create tiny bubbles of gas or cavities in the body. 2 Laser Radiation a Physical characteristics The name "LASER" is an acronym for "Light Amplification by Stimulated Emission of Radiation". The light that comes from a conventional light source radiates in all directions and in various wavelengths that reinforce or cancel each other. Light from a laser beam travels in one direction in straight line and in a specific wavelength only; thus, the laser beam is a very narrow beam. Laser radiation may be released either as a pulse or a continuous wave radiation. Typical power output ranges from 0.02 watt to 100,000 watts. With the aid of a "Q-switch" device, the laser pulse- width could be much shortened whereby producing extremely high power pulses. Laser beams are not limited to visible wavelengths only. Though a laser beam produces only one wavelength, laser units can be designed over a wide range of frequencies, from infrared to ultraviolet regions. 5 b Laser Sources Basically, a laser system consists of two accurately parallel reflecting end-plates between which the active lasing material is placed, one plate being slightly transparent. The active lasing material is pumped by exciting its atom or molecule to an excited state. A light wave is then emitted when an excited atom falls from the excited energy state to a lower energy state. Light waves emitted parallel to the axis of the active lasing material are reflected back and forth between the two end-plates and stimulate other atoms or molecules to emit light wave of the same frequency. When amplification is great enough, a laser beam would pass through the partially reflecting end plate. There are four types of lasing systems i solid state, i.e. ruby crystal is most common, ii gaseous state, i.e. CO2 and He-Ne are most common, iii semiconductor, GaAlAs gallium-arsenide junction is common, iv liquid state, organic dyes lasers. c Classification of Laser The hazard classification specified for laser are defined by the output parameters, i.e. emission wavelength, emission duration, power output, and accessible emission levels (AELs) of laser radiation. The maximum accessible emission levels for various classes of lasers are specified in the Second Schedule to the Radiation Protection (Non-Ionising) Regulations 1991. The classes are as follow:- Class 1 laser systems are safe by virtue of their power output or engineering design. These lasers cannot be considered as hazardous even if all of the accessible laser radiation output is to direct to the eye's pupil or focuse into one mm spot on the skin for a day. These lasers are considered as non-risk lasers, or exempt lasers. The wavelengths could range from ultraviolet, visible to infrared region. Class I continuous visible laser should not have the accessible laser output of more than 0.39 microwatts. Class 2 laser systems are those emitting visible laser radiation, in the wavelength range from 400 nm to 700 nm, in pulse or continuous wave. This is a class of low-power and low-risk lasers. 6 These laser systems are normally not hazardous by virtue of normal aversion responses. They are not capable of causing any eye injury within the duration of a blink of 0.25 sec. For class 2 continuous visible laser devices, the power emitted should not exceed one mW, bar code scanner at the check out point in supermarket and laser pointer in class room are good examples for class 2 laser. Any low- risk laser devices, by virtue of enclosure, should have warning labels indicating "High-risk class when access panels are removed". Class 3 laser systems are considered to be medium-power and moderate-risk laser. Generally, they do not present any diffuse reflection hazard, skin hazard for unintentional exposure, or fire hazard. These lasers could present a serious potential eye injury resulting from intra-beam viewing of the direct beam and specula reflections. Class 3 laser can be further sub-divided into two subcategories, namely, class 3a and class 3b lasers. i Class 3a lasers are capable of emitting visible and/or invisible laser radiation with the maximum accessible emission levels as specified. As for visible Class 3a laser devices, they operate in a power range of 1 -5 mW, which have an irradiance in the emergent beam of not more than 25 W/m 2. This class of laser are not capable of damaging the eye because of the person's normal aversion response to bright light, unless the radiation is stared at for a long time, or unless binoculars or optical instruments are used. Many construction alignment laser fall into the class 3a category. II Class 3b lasers are medium-power and moderate-risk laser devices that are capable of emitting ultraviolet, visible or infrared laser radiation with specified maximum accessible emission levels. It can be in continuous wave or pulsed mode and operating in a power of 500 mW or less for emission duration of longer than 0.25 sec, or a radiant exposure of 100 kJ/m2 or less for emission duration shorter than 0.25 sec. These lasers are capable of causing accidental injuries by exposure from the direct or specularly reflected beam. Diffuse laser beam reflections from class 3b are not hazardous, but may be so if focused to the eye with optical instruments. Therapeutic laser, acupuncture laser, bio-stimulation lasers, 7  military laser range finders and designator are all under class 3b lasers. Class 4 lasers are high-power and high-risk lasers that are capable of emitting ultraviolet, infrared or visible laser radiation at levels exceeding the accessible emission levels for class 3b. The average power output of 500 mW or greater for periods longer than 0.25 sec, or a radiant exposure of 100 kJ/m2 within an exposure duration of 0.25 sec or less. These lasers can produce a hazardous direct or specularly reflected laser beam. A potential fire and skin burn hazard exist as the possibility of hazardous diffuse reflections occur. d Laser applications Forty three years after Einstein first introduced the concept of stimulated emission of radiation by atomic systems in 1917, the first working laser, ruby crystal laser, was produced in 1960. Few months later, the first HeNe laser was then produced at Bell. To date, more than forty years after the invention of the first ruby and HeNe lasers, lasers have found their applications in medical and industrial fields. i Industrial High power laser has led to its use in industrial cutting (300 - 1500 W), drilling, welding (500 - 600 W) and micro-machining. Its highly collimate beam has also been used to project a reference line for construction equipment (2 mW) in such operations as dredging, tunnelling, pipe laying and bridge building. Other industrial applications include trimming, marking, curing and entertainment laser light show. Common high-power industrial lasers are, * Industrial cutting * Drilling, welding * Marking * Engraving * Micro-machining * Communications field * Entertainment lasers 8  Other low-power industrial lasers are, * Construction alignment lasers * Dredging * Tunnelling, pipe laying * Bridge building * Military applications * Scanners for deciphering coded package markings * Low power Entertainment laser ii Medical Lasers that are manufactured for purpose of in vivo diagnostic, surgical, therapeutic laser irradiation of any part of human body are classified as medical lasers. Medical lasers are used in areas of plastic surgery, ophthalmic, physiotherapy, obstetrics and gynaecology. Photo-coagulator laser (1 - 3 W) is used by some surgeons to repair torn retinas. A limited beam laser has also been used to kill malignant tissue, remove birthmarks or burn away warts. Statistics in 2007 show that there were 518 units of medical lasers and 779 medical laser users in Singapore. Out of these medical lasers, about 453 units were class 4 high power surgical lasers and they were being used by 692 medical practitioners and surgeons in various major hospitals and clinics. Acupuncture and cosmetic lasers are categorised as medical lasers. High-power medical lasers are used in, * Surgery * Excision of malignant or non-malignant tissues * Plastic surgery * Removal of birthmarks * Obstetrics and gynaecology * Burning away warts * Photo-coagulator for torn retinas by ophthalmologist The low power medical lasers and they are, * Acupuncture lasers * Physiotherapy lasers * Cosmetic lasers In Singapore, these low power medical lasers could easily be found in various physiotherapy centres, acupuncture centres and beauty 9  saloons. The 2007 statistic showed that there were 44 units of class 3b low power therapeutic medical lasers that were used by 37 physiotherapists, 9 Chinese Physicians and 8 beauticians. iii Research Lasers are also used in Singapore for research and educational purposes. In 2007, there were about 362 researchers involved in using about 328 lasers for their projects. Most of the lasers are less than 5 W and they can be as high as 1000 W, i.e. class 4 CO2. e Laser radiation hazards and its exposure limits Ocular Exposure to Laser Radiation Lasers can be hazardous due to its great brightness of beam. The main concern is with the eye damage, as it is capable of increasing the laser light intensity many thousands of times by its focusing power. Parallel rays of a laser may be focused to a point image by the eye while rays from a conventional lamp can produce a sizeable and less dangerous image at the retina. Light from a laser entering the eye is concentrated 100,000 times at the retina. Thus, the eye is, by far, the organ of the body most subject to damage. Skin Exposure to Laser Radiation Injury to skin is seldom of concern except in dealing with very high- powered lasers. But with ever increasing laser intensities encountered, skin damage is becoming a concern. Exposure limits The unit used to describe the radiation exposure from laser radiation is completely different from the units for ionising radiation exposure. The common units are Watts ( W ) or milliwatts (mW ) for the power or W/m2 or mW/cm2 for the intensity. The exposure limits (ELS) should be used only as guidelines for controlling human exposure to laser radiation. They should not be regarded as thresholds of injury or as sharp demarcations between "safe" and "dangerous" exposure levels. Exposure at levels below the ELs should not result in adverse health effects. They incorporate the collective knowledge generated world-wide by scientific research and laser safety experience, and are based upon the best available published information. In 1985, International Non-ionising Radiation Committee (INIRC) of the International Radiation Protection 10  Association (IRPA) published a set of guidelines on limits of exposure to laser radiation of wavelengths between 180 nm and 1 mm. They are used as for given wavelength ranges. ELs for the eye are always specified at a plane tangent to the cornea at the point of the optical axis of the eye. In addition to the exposure limits, all precautions must be observed during laser operation. f Safety guides against laser radiation (a) Laser radiation should be discharged in a background that is non-reflective and fire resistant. (b) The area should be cleared of personnel for a reasonable distance on all sides of laser beam. (c) Warning sign should be attached to laser equipment in a conspicuous location indicating the potential eye hazard associated with laser. (d) Looking into primary laser beam should be avoided at all times, and equal care should be exerted to avoid looking at specula reflections of the beam, including those from lens surfaces. (e) Avoid aiming laser with eye and prevent looking along the axis of the beam, which increases the hazard from reflections. (f) Laser work should be carried in areas of high general illuminations to keep pupils constricted; thus, limit energy which might inadvertently enter the eyes. (g) Laser radiation workers should be instructed on potential eye hazards and the importance of limiting unnecessary exposure. They should receive pre-employment, periodic and final eye examinations. (h) Safety eyewear designed to filter out specific frequencies characteristic of the system affords protection, but it may only be partial. (i) Binoculars or aiming telescopes should not be used to view 11  direct beam or reflected beam from mirrors unless the beam intensities are greatly below the safe levels. If necessary, a filter having sufficient optical density should be placed in the optical path of telescope for such situations or adequate laser protective eye wear is worn by the operator. (j) At its maximum emission capacity, a high power laser should operate in such a manner that the intensity of laser radiation at all accessible locations, when measured within a stationary circular area of 0.385 cm 2 and averaged over that area does not exceed the following limits * at any time interval of less than 18 sec, an integrated irradiance of 5.0 x10 - 3 J/m 2 * at any time interval t sec, that is greater than 18 sec but less than or equal to 10 sec, an integrated irradiance of 18 t 0.75J/m2 * at any time interval of greater than 10 sec but less than or equal to 10,000 sec, an integrated irradiance of 100 J/m 2 * at any time interval of greater than 10,000 sec, an irradiance of 10 mW/m2 Since high power lasers are capable of cutting and burning, certain form of control in operating these lasers is required. Only the trained and qualified persons are allowed to use the high power lasers in most of the advanced countries. As for the use of low power lasers, it can also cause injury to the eyes if they are handled and used incorrectly by untrained personnel. Thus, there is a need to restrict its users to trained personnel only. 3 The Radiation Protection Act 2007 The Radiation Protection Act was enacted to regulate, by means of licensing and penalty, the importation, manufacture, sale, transport, keeping and use of radioactive materials and irradiating apparatus. Every licensee is responsible for the radiation safety of workers under his supervision. The Act was first published in April 1973 as The Radiation 12 Protection Act, 1973 and it came into operation on the 1 Sep 1974. Two sets of regulations, Radiation Protection Regulations 1974 and Radiation Protection (Transport of Radioactive Materials) Regulations 1974, were formulated under the Act to impose detailed requirements in dealing with radioactive materials and ionising irradiating apparatus. To ensure the safe use of certain potentially hazardous non-ionising (NIR) devices in Singapore, the Radiation Protection Act 1973 was repealed and The Radiation Protection Act 1991 was passed in the Parliament and had brought some potentially hazardous NIR devices under control. The devices now under control are high power lasers, entertainment lasers, ultrasound, microwave ovens, sunlamps, X-Ray machines and radioactive materials. The Act specifies the activities requiring licences, the requirements for obtaining licences, powers for the promotion of radiation safety and the penalties for offences committed. The activities requiring licences include manufacture, sale, keep, use, importation and exportation of devices. The first set of regulations formulated under the new Act to impose detailed requirements in dealing with Non-ionising Radiation irradiating apparatus was published on the 1 Nov 1991 and it came into operation on the 1 February 1992. In 2007, the Radiation Protection Act (Chapter 262) was repealed and re-enacted to transfer the authority from the Health Sciences Authority to the National Environment Agency. The Radiation Protection (Ionising Radiation) Regulations 2000 This set of regulations was first published and came into operation on 1 Sep 1974. Due to the new development in the field of radiation protection and the new recommendations of the International Commission on Radiological Protection under ICRP Publications 60 and 61, the Regulations was amended, updated, re-arranged and published as Radiation Protection (Ionising Radiation) Regulations 2000 on February 2000. Some of the main provisions contained in the Regulations are outlined below. * Licences are required for manufacture, possession, use and sale of radioactive materials and irradiating apparatus. A licence is required for importing or exporting each consignment of radioactive materials or irradiating apparatus. 13 * Radiation workers must be over 18 years of age. They are required to register, under medical supervision, wearing personal dosimeters (e.g. TLD, film badges) and adequately instructed to do radiation work. No radiation worker is permitted to receive a dose in excess of the Maximum Permissible Dose in the course of his work. * All radioactive materials, irradiating apparatus and radiation areas must be appropriately labelled to give adequate warning of radiation hazards. * Suitable arrangements must be made for the safe storage and accounting of radiation sources. Sealed sources must be leak tested at least once a year. * The design of each installation or laboratory on such aspects as shielding, interlocks, warning devices, lay out, instrumentation, ventilation and surface finishes must meet the applicable requirements. * Radiation level at the area outside radioactive storage area that is accessible to the public members should be less than 0.5 Sv/hr. * Radiation level outside an X-Ray room (medical or industrial) should be less than 10 Sv/hr. * Radiation level at the area outside the boundary defined for NDT work site should be less than 25 Sv/hr. * Appropriate procedures must be followed in working with radiation sources and in dealing with radiation accidents. * For medical applications, only radiologists are allowed to hold licences to use X-ray machines for diagnostic and therapeutic applications. The Radiation Protection (Transport of Radioactive Materials) Regulations 2000 This set of regulations was first published as The Radiation Protection (Transport of Radioactive Materials) Regulations 1974 and came into 14  operation on 1 Sep 1974. To be in line with the latest revision of the International Atomic Energy Agency's (IAEA) regulations on the transport of radioactive materials (IAEA Safety Standards Series No. ST-1, 1996 Edition), this set of regulations was amended, updated, re-arranged and published as Radiation Protection (Transport of Radioactive Materials) Regulations 2000 on February 2000. Some of the main provisions contained in the Regulations are outlined below. * Licence L6a from Director of Radiation Protection & Nuclear Science Department, National Environment Agency, is required for transporting radioactive materials within Singapore. Licensee is required to make arrangement to control the radiation exposure of his workers. * Placards with radiation hazard logo should be placed on both sides of the vehicle whenever it is carrying radioactive material. A vehicle with radioactive materials inside should never be left unguarded at all time. * Within the vehicle, the radiation level at places occupied by any individual should not exceed 20 Sv/hr unless this individual is a registered radiation worker or he is provided with a personal monitoring badge. * Vehicle with radioactive material inside should not carry any individual unconnected with the transport or use of the radioactive material or any individual less than 18 years of age. * Requirements for packaging and transport, including labelling, external surface contamination levels, segregation from persons and films, and the design and testing of packages etc. must be complied with according to the packaging type, activity contained, radiation level outside the package, and the mode of transportation. * Licensee / shipper / consignor is responsible for the safety and correctness of his packaging and labelling and for assuring the carrier that all applicable regulations have been fulfilled. 4 Radiation Protection (Non-Ionising Radiation) Regulations 1991 The first set of regulations formulated under the new Act to impose 15 detailed requirements in dealing with Non-ionising Radiation irradiating apparatus was published on 1 Nov 91. The new Act and new Regulations came into operation on 1st February 1992. It applies to the following NIR irradiating apparatus: a Ultraviolet sunlamps Sunlamp means ultraviolet lamp or apparatus incorporating one or more ultraviolet lamps intended for irradiation of any part of living human body, by ultraviolet radiation with wavelengths in the air between 180 nm to 400 nm, to induce skin tanning or other cosmetic effects. b Microwave ovens Microwave oven means a device designed to heat, cook or dry food or material within a cavity through the application of microwave energy with the frequency ranges from 890 MHz to 6 GHz and is used in an industrial establishment, a commercial establishment, a restaurant, a cafeteria, in or with a vending machine, or in the home. c Medical and industrial ultrasound apparatus Ultrasound apparatus means medical diagnostic apparatus, medical therapeutic apparatus and industrial apparatus designed to generate and emit ultrasonic power at acoustic frequencies above 16 kHz. d Magnetic resonance imaging (MRI) Apparatus Magnetic resonance imaging apparatus means any medical diagnostic apparatus designed to emit magnetic field and radio- frequency radiation for the purpose of imaging or spectroscopy of human body or both. e Entertainment lasers Entertainment laser means any laser, laser facility or mobile laser system designed for used in laser light shows. f High power lasers Radiation Protection (Non-ionising Radiation) Regulations 1991 allow only the trained and qualified personnel to operate the high power lasers in Singapore. High power laser means any industrial 16  and medical laser apparatus from Class 3b and Class 4 based on the classification set out in Regulations. For a person to engage in any radiation work with any laser, he must be at least 18 years old, has been adequately trained, has special knowledge in the safe use of laser and holds a licence authorising him to operate the lasers. In addition, a licence to use Class 4 medical lasers may be granted to registered medical practitioners and registered dentists only. Types of licences related to lasers are * Licence to manufacture, possess for sale or deal in lasers * Licence to keep or possess for use of lasers * Licence to operate or use lasers * Licence to import or export lasers Any one found using class 3b & 4 lasers without licence in Singapore would be charged for violating the Act and could be fined up to maximum of not than $10,000 or imprisonment for a term of not exceeding 12 months or both. Types of licences Issued by RPNSD for manufacture, sale, possession and use of Non-Ionising Radiation apparatus Application Reference Fee N1 Licence to manufacture or deal with Microwave $210 per ovens, UV sunlamps, medical and industrial annum ultrasound devices, Magnetic Resonance Imaging (MRI), class 3b & 4 high power medical and industrial lasers and all classes of entertainment 17  lasers N2 Licence to keep or possess for use of high power $155 per ( Power > 50 Watt) industrial ultrasound annum cleaners, ultrasound welders, ultrasound cutter etc, medical diagnostic ultrasound, therapeutic ultrasound, surgical ultrasound, Magnetic Resonance Imaging (MRI), class 3b & 4 high power medical and industrial lasers and all classes of entertainment lasers N3 Licence to use class 3b & 4 high power medical $105 per and industrial lasers and all classes of annum entertainment lasers N4a Licence to import Microwave ovens, UV $ 40 per sunlamps, medical and industrial ultrasound consignment devices, Magnetic Resonance Imaging (MRI), class 3b & 4 high power medical and industrial lasers and all classes of entertainment lasers N4b Licence to export high power ( Power > 50 Watt) $ 40 per industrial ultrasound cleaners, ultrasound consignment welders, ultrasound cutter etc, medical diagnostic ultrasound, therapeutic ultrasound, surgical ultrasound, Magnetic Resonance Imaging (MRI), class 3b & 4 high power medical and industrial lasers and all classes of entertainment lasers 18