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IJk Health and Welfare Sante et Bien-etre social Canada Canada 79-EHD-41 recommended safety procedures for the selection and use of demonstration-type gas discharge devices in schools Recommended Safety Procedures for the selection and use demonstration-type gas discharge devices in schools CONTINTS Pag_e 1 INTRODUCTION 1 >. G<\5 DISCHARGE TUBES 2 ?. 1 Col d Cathode X-ray Tube 3 2.7. Shadow or Fluorescent Effect Tube i 1.3 Magnetic or Deflection Effect Tube 3 2.4 Heat Effect Tube 4 2.5 High or Low Vacuum Effect Tube 4 2.6 Other Gas Discharge Tuoes 4 3. RADIATION HAZARDS 5 3.1 1972 Radiation Protection Bureau Survey 5 3.2 Exposure Rates 5 3.3 Poor Demonstration Procedures 6 4. STANDARDS FOR NEW GAS DISCHARGE DEVICES 8 ::., RECOMMENDED SAFETV PRECAUTIONS 9 5.1 General Safety Recommendations 9 5.2 Specific Recommendations 9 5.2.1 X-ra.y Tubes 9 5.2.2 Other Gas Discharge Tubes 10 REFERENCES 11 APPENDIX 1: Dose Equivalent Limits for Pupils in Schools 13 APPENDIX 2: Radiation Emitting Devices Regulations for Demonstration-Type Gas Discharge Devices 1L. TABLES 19 FIGURES 21 (SEE REVERSE SIDE) Page 17 STANDARDS OF FUNCTIONING 5. Every device shall function in such a way that the emission of X-rays therefrom, under all possible conditions of operation and for as long as the device has its original components or has replacement components recommended by the manufacturer, is such that the average exposure rate of X-rays to an object having a 10 square centimetre cross section and centred at 5 centimetres from any accessible external surface of the device does not exceed 0.5 mi 11iroentgen per hour. RECOMMENDED SAFETY PROCEDURES FOR THE SELECTION AND USE OF DEMONSTRATION-TYPE GAS DISCHARGE DEVICES IN SCHOOLS Environmental Health Directorate Health Protection Branch Published by authority of the Minister of National Health and Welfare 79-EHD-41 COPIES OF THIS REPORT CAN BE OBTAINEO FROM: Information Directorate Department of National Health and Welfare Brooke Claxton Building Ottawa, K1A 0K9 CONTENTS Page 1. INTRODUCTION 1 2. GAS DISCHARGE TUBES 3 2.1 Cold Cathode X-ray Tube 4 2.2 Shadow or Fluorescent Effect Tube 4 2.3 Magnetic or Deflection Effect Tube 4 2.4 Heat Effect Tube 5 2.5 High or Low Vacuum Effect Tube 5 2.6 Other Gas Discharge Tubes 5 3. RADIATION HAZARDS 7 3.1 1972 Radiation Protection Bureau Survey 7 3.2 Exposure Rates 7 3.3 Improper Use Procedures 8 4. STANDARDS FOR NEW GAS DISCHARGE DEVICES 11 5. RECOMMENDED SAFETY PRECAUTIONS 13 5.1 General Safety Recommendations 13 5.2 Specific Recommendations 13 5.2.1 X-ray Tubes 13 5.2.2 Other Gas Discharge Tubes 14 REFERENCES 15 APPENDIX 1: Dose Equivalent Limits for Pupils in Schools 17 APPENDIX 2: Radiation Emitting Devices Regulations for Demonstration-Type Gas Discharge Devices 19 TABLES 23 FIGURES 25 ui FOREWORD Modern science laboratories in educational institutions employ as teaching aids a variety of equipment for demonstration and experimentation. Many of the devices used are capable of emitting X-rays, microwaves or other potentially hazardous radiations at levels greater than considered acceptable. One class of demonstration device in widespread use in schools is the gas discharge tube. Some gas discharge tubes, in particular the cold cathode type, can emit X-rcvs at signi- ficantly high levels. Unless such tubes are used carefully, and with due regard for t^ood radiation safety practices, they can result in exposures to students that are in excess of the maximum levels recommended by the International Commission on Radiological Protection. This document has been specially prepared to assist science teachers and others using demonstration-type gas discharge devices to select and use such devices so as to present negligible risk to themselves and to students. It contains useful information on safety proce- dures that should be followed when performing these demonstrations or experiments. Clearly a document such as this cannot cover all possible situations, nor can it substitute for the exercise of sound judgement, so the recommendations may need modification in unusual ci. ;um- stances. Interpretation or elaboration on any point in this document can be obtained by contac- ting the Radiation Protection Bureau in Ottawa. This document was drafted by Dr. W.M. Zuk and Mr. E. Rabin. AVANT-PROPOS Dans les laboratoires de sciences modernes des établissements d'enseignement, divers appareils sont employés comme outils didactiques à des fins de démonstration et d'expérimentation. Bon nombre de ces appareils peuvent émettre des rayons X, des micro-ondes ou d'autres rayonnements potentiellement dangereux à des intensités de rayonnement supérieures aux limites acceptables. Le tube à décharge est l'une des catégories de dispositifs pour démonstrations dont l'usage est répandu dans les écoles. Certains de ces tubes, particulièrement les tubes à cathode froide, peuvent émettre des rayons X dont l'intensité est très élevée. Si les personnes qui utilisent de tels tubes ne sont pas prudentes ou n'observent pas les mesures de protection contre les rayonnements, les élèves peuvent être soumis à des irradiations supérieures à celles qui sont recommandées par la Commission internationale de protection contre les radiations. Le présent document s'adresse particulièrement aux professeurs de sciences et à d'autres personnes qui emploient des dispositifs à décharge pour démonstration, afin de les aider à choisir et à utiliser de tels dispositifs de manière à ce que leurs élèves et eux-mêmes courent le moins de risques possible. Le document renferme des renseignements utiles sur les mesures de sécurité à observer au cours des démonstrations ou des expériences. Il est évident qu'un document du genre ne peut couvrir toutes les situations possibles ni remplacer le bon sens. Il se peut donc que les recommandations doivent être modifiées dans des circonstances particulières. On peut obtenir des explications ou des éclaircissements sur des aspects quelconques du document en communiquant avec le Bureau de la radioprotection à Ottawa. Le présent document a été rédigé par Messieurs W.M. Zuk et E. Rabin. VI 1- INTRODUCTION In Canada, as in many other countries, increasing numbers of demonstrations and experiments in school science programs involve use of potential sources of ionizing radiation. As a result, large numbers of students under the age of 18 years are susceptible to being unneces- sarily exposed to ionizing radiation. It is particularly important that all such exposure be avoided. Because it occurs at an early age, any gonadal irradiation from such demonstrations makes for maximum contribution to the population genetic dose. For this and other reasons, 1 2 the International Commission on Radiological Protection (I.C.R.P.) has recommended ' dose limits for pupils in schools of one-tenth of the dose limits recommended for individual member?; of the public. In 1972 the Radiation Protection Bureau surveyed secondary schools in the Ottawa area to determine what demonstration-type radiation emitting devices were available in the schools and to assess the nature and extent of hazards associated with their use. Particular emphasis was placed on gas discharge tubes because of an earlier U.S. study which revealed that cold cathode gas discharge devices were widely available in U.S. schools and were capable of emitting X-rays at hazardous levels. The results of the Ottawa area study, described briefly in section 3, confirmed the U.S. findings and pointed to the need for regulatory action to control demonstration-type gas discharge devices. The survey results also strongly indicated that there was a definite need for safe use guidelines for such devices. Interim guidelines were produced and widely circulated in Canada shortly after the results of the survey were known. The intent of this document is to formalize the interim guidelines and to provide more comprehensive recommendations which, when adhered to, will ensure that demonstration- type gas discharge devices present no radiation hazard either to pupils or teachers. - 2 - 2. GAS DISCHARGE TUBES For many years, gas discharge tubes have been in widespread use in schools for experi- mental treatment of atomic physics. These devices are designed to demonstrate the production, properties and effects of electrical discharges in gases and the luminous phenomena which accompanies them. Some discharge tubes are specifically designed to generate X-rays; in others, X-ray emission is incidental to the intended purpose. In its basic form, a gas discharge tube consists of a partially evacuated, sealed glass tube, containing the gas of interest at a predetermined pressure, and two or more electrodes for applying a high voltage to the enclosed gas. Gas discharge tubes are usually classified in accordance with the means used to produce electron emission from the cathode. Discharge tubes in which the electrons are produced by means of thermionic emission are referred to as hot cathode tubes. By employing a heated filament to produce the electrons, such tubes have been designed to demonstrate the desired effects with operating voltages below 5000 volts and without accompanying x-rad'ation. Several demonstration-type hot cathode tubes are available commercially. In the 1972 survey, referred to in Section 1, no x-radiation was detected from such tubes when operated at voltages within the manufacturer's specified operating range. The second catagory of discharge tubes does not employ a heated cathode; the electrons are released from the cold cathode surface by positive ion bombardment. The positive ions are generated by ionization of gas atoms contained in the tube. Such tubes are classified as cold cathode tubes. A variety of high voltage sources is used to operate cold cathode discharge tubes, but induction coil power supplies, because of their low price, are used most frequently.
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