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RADIATION SAFETY MANUAL
Section 13: Non Ionising Radiation

INDEX
13.1 Introduction
13.2 Lasers
13.3 Ultraviolet Radiation

13.1 INTRODUCTION

Non-ionising radiation is distinguished from ionising radiation, the subject of the rest of the manual, by the different mechanism of interaction with matter. Whereas ionising radiation ionises atoms within the tissue, non-ionising radiation interacts differently with human tissue, for example by generating heat. Although x-rays and gamma rays are part of the electromagnetic spectrum, the term "non-ionising radiation" (NIR) encompasses wavelengths from visible light to microwave and also includes ultrasound. For the purposes of this manual, the only NIR radiations discussed are lasers, ultraviolet, microwave and ultrasound.

Supervisors and staff using lasers of classifications III (a and b) and IV, should make themselves familiar with the Australian Standard - Laser Safety (ASS 2211-1991).

13.2 LASERS

13.2.1
Introduction
 

The word "LASER" is actually an acronym for "Light Amplification by Stimulated Emission of Radiation" and is commonly applied to devices which emit an intense, coherent and highly directional beam of "light". Laser radiation covers the infra red, visible and ultra violet regions, depending on the type of laser. The most common interaction with tissue is production of heat which, because of the highly intense nature of the laser beam and its ability to be finely focused, can be generated in very large quantities, sufficient to evaporate tissue and cause a large amount of damage in a very short time.

Lasers are divided into classes, depending on the power output and the risk of damage from accidental exposure. The classes are:

Class 1 - intrinsically safe
Class II - low power devices emitting visible light - not completely safe, but the blink reflex will protect the eye
Class IIIa - similar to Class II, except that, if the beam is focused onto the eye by, say, binoculars, the beam could be hazardous
Class IIIb - either the blink reflex is not fast enough to prevent damage, or the beam is invisible and therefore the blink reflex cannot work
Class IV - high power devices capable of causing immediate injury to the eye or skin - diffuse reflections may be hazardous

Most medical lasers are in Class IV, the most hazardous.
The principle hazard is damage to the eye. Laser radiation in the visible and near infra red wavelength regions can penetrate the eye and damage the retina, possibly permanently, while ultraviolet laser radiation and far infra red radiation can damage the surface of the eye. Most lasers used in medicine are very high power devices and damage can occur in a fraction of a second far quicker than the eye can blink to shut off the beam. The hazard arises mostly from accidental reflections of the beam from shiny objects.

For staff using lasers it must be stressed that damage is most likely immediate and often permanent - thus the operating rules which are given for each installation (local rules) must be understood and adhered to by all staff involved.
13.2.2 Administrative Arrangements
 

Overall control of safety aspects of the use of lasers within The University of Newcastle rests with the Occupational Health and Safety Committee (OHSC). The Radiation Committee shall recommend and maintain policies and regulations for the control of laser hazards.

The Vice-Chancellor through the Occupational Health and Safety Committee shall appoint a Laser Safety Officer (LSO), the Occupational Health and Safety Committee to have routine authority for supervision and control of laser hazards. The range of duties of the LSO shall be similar to those for the Radiation Safety Officer.

One person at each installation shall be designated as the laser supervisor, who shall be responsible for day-to-day safe use of the laser.

In the absence of licensing under State Radiation Regulations as with ionising radiation, ALL WISHING TO OPERATE LASER UNITS OF CLASS IIIB AND ABOVE SHALL BE REGISTERED WITH THE OCCUPATIONAL HEALTH AND SAFETY COMMITTEE TO DO SO. NO PERSON WHO IS NOT REGISTERED SHALL OPERATE ANY LASERS OF CATEGORIES IIIB AND IV. Registration will require training in both the medical and physics/safety aspects of lasers.

All laser facilities shall be registered and be surveyed for safety hazards before operations can commence. The Laser Safety Officer shall be consulted in the planning stages of any new laser facility.

All staff who are required to work with any laser should receive basic training on the hazards of lasers and safe working practices. This training could be provided by the Laser Safety Officer or other persons competent to do so.

All staff who are required to work with a class IV laser shall undergo a baseline eye examination before commencing work with the laser followed by 2 yearly examinations and/or an examination on leaving the institution. Further examinations shall be performed in the case of a known or suspected accident/incident.
13.2.3 Responsibilities
 

Laser Supervisor
The laser supervisor shall be responsible for:

1. only permitting operation of the laser when there is adequate control of laser hazards.
2. liaison with the laser safety officer on such matters as hazard evaluation and medical surveillance.
3. reporting of known or suspected accidents or incidents and ensuring that medical examinations of staff involved are arranged.
4. ensuring that all new employees required to work with the laser are adequately instructed on safety measure.
5. ensuring that there is available to staff an adequate supply of protective eyewear for the particular laser in use.

Employees
Employees are responsible to some degree for their own safety. In particular, they shall not work with or near a laser unless authorised to do so and shall at all times comply with safety measures prescribed by the laser supervisor and the Safety Officer. Further, if they know or suspect that an accident or incident has occurred, they shall immediately inform the laser supervisor and complete a mishap report.
13.2.4 Medical Surveillance
 

As mentioned in Section 13.2.2, many staff working with Class IV lasers are to have a baseline eye examination prior to commencement of work with the laser and at termination as well as twelve monthly routine examinations. In case of accidental exposure, a further examination should be performed.

Australian Standard AS2211-1991 outlines the required ocular examinations, including a test of visual acuity, central visual fields and fundus examination. Any deviation from acceptable performance will require identification of the underlying pathology by testing as deemed appropriate by the examining medical officer.

Ocular History
The past eye history and family history shall be reviewed. Any current complaints concerned with the eyes are noted. Inquiry should be made into the general health status with a special emphasis upon systematic diseases which might produce ocular problems. The current refraction prescription and the date of the most recent examination should be recorded.

Visual Acuity
Visual acuity for far and near vision should be measured with some standardised and reproducible method. Refraction corrections should be made if required for both distant and near test targets. If refractive corrections are not sufficient to change acuity to 20/20 (6/6) for distance, and Jaeger 1- for near, a more extensive examination is indicated.

Macular Function
A Humphrey's automated visual field test should be performed as a screening test, ie not the full examination.

Contrast Sensitivity
Contrast (or glare) sensitivity should be documented by the Arden sine wave patterns or similar acuity tests which include low constant images.

Examination of the Ocular Fundus with an Ophthalmoscope
The macula should be checked by a medical officer.

EXAMINATIONS FOLLOWING SUSPECTED ACCIDENTAL EXPOSURE

If it is suspected that an accidental eye exposure has occurred, the incident should be reported to the laser supervisor immediately, and arrangements made for medical examination. The case should be handled as an eye trauma, and the necessary examinations determined by the John Hunter Eye Clinic.

13.3 ULTRAVIOLET RADIATION
Ultraviolet (U/V) radiation can cause a number of hazards, the most grave being the induction of skin cancer. Exposure is most likely to occur from the sun, and it is well known that there is a link between sunlight and skin cancer. In fact, the permissible weekly levels of occupational exposure to UV are exceeded in a few hours of exposure to the summer sun!

Ultraviolet radiation is used mainly in the University to view electrophoretic gels for and for disinfection of fume hoods. It is commonly divided into three wavelength bands, UV-A (400-315nm), UV-B (315-280 nm) and UV-C (280-100 nm). Most medical applications of ultraviolet are in the UV-A and UV-B regions.

The hazards to staff are to the eye and to the skin. No person should look at a UV source without eye protection. As mentioned, it is well known that excessive UV irradiation, particularly to fair skin, can be carcinogenic. The operator may need to wear UV shielding goggles to protect the eyes. Skin protection can be achieved simply by clothing made from tightly woven fabric.

There is no monitoring method commonly available for ultraviolet radiation and staff must follow any procedures laid down for use of ultraviolet in their department.

13.4 MICROWAVE AND RADIO FREQUENCY (RF) RADIATION
This is also electromagnetic radiation covering the frequency range from 300 kHz - 300 Mhz (RF) and 300 Mhz - 300 Ghz (microwave).

Microwave radiation appears in Universities mainly in microwave ovens but also there are some microwave communication transmitters. Its effect on tissue is mainly heating, and the organ most at risk is the eye. Microwave ovens should be tested regularly for leakage around the door, the most likely source of accidental exposure. This is the responsibility of the Lab Supervisor.

Radiofrequency radiation also has a heating effect, but the risk over the whole frequency range is not fully understood. The maximum recommended exposure levels are in the range 1-5 mW/cm2.

13.5 EXTRA LOW FREQUENCY (ELF) RADIATION
This concerns mainly power frequencies, ie normal domestic electricity supply. Here we are concerned with electric and magnetic fields. The electric fields is that which (at high levels) generates sparks, similar to static electric fields. The magnetic field is normally not perceptible, although very high levels can cause visual or cardiac effects. The effects of low level ELF radiation are difficult to measure since the incidence appears to be very low.

Although power lines cause most public concern, the fields from VDUs the electron microscope and domestic appliances such as hair dryers and vacuum cleaners can be higher.

There is no known hazard from ELF radiation in the normal University working environment.