EXPOSURE TO RADIOFREQUENCIES IN HOSPITAL REHABILITATION SERVICES

Transcription

1 EXPOSURE TO RADIOFREQUENCIES IN HOSPITAL REHABILITATION SERVICES A. Perramon Lladó, J. Aniés Escartín Area de Higiene de Agentes Físicos. Dirección Seguridad e Higiene, ASEPEYO Mutua de Accidentes de Trabajo y Enfermedades Profesionales de la Seguridad Social N 151 aperramonllado@asepeyo.es INTRODUCTION The exposure to non-ionizing radiation for the physiotherapists in charge of health treatments based on electrotherapy, due to the use of short wave and microwave equipment, is often significant. In this study, we have measured and assessed the emission of non- ionizing radiation from short wave equipment at a frequency of 27,12 MHz, and the emission of microwave equipment at a frequency of 2,45 GHz for a Rehabilitation Service of a Mutual. The measure of radio frequencies and microwaves has been done with two different meters, both suitable for the kind of measure we needed to carry out. One of them used a shaped probe according to the limit values curve of the ICNIRP98 1 which gives as a result a percentage (%) of the electric field measured compared with the mentioned limit curve. The second meter gives the value of the field in its own physical units. Those measures were compared with the valid limits established for working environments, which are the ones proposed by the ICNIRP98 and adopted by most of the European countries. Taking into account the limit values curve of the ICNIRP, when we assess radio frequencies emitted from the short wave equipment, we find that we are working in the middle of the most critical range of the curve (10 to 400 MHz), whereas in the case of the microwaves, we are near that lowest-limit range of the curve. Some bad habits, such as the case of health workers suffering unnecessary exposure due to the fact of giving instructions and explanations to patients during treatment, or the inadequate lay-out of the radiating machines in small spaces, worsen the situation which must be controlled from the first moment, considering that electrotherapy machines at high frequency can produce important levels of radiation. This study quantifies and estimates the exposure that affect a significant number of health workers who operate electrotherapy machines in the Rehabilitation Services of hospitals, at the same time that proclaims the need to take action in order to assure that this type of exposure related to bad habits does not give place to real threats for the health of the affected workers. METHODOLOGY The use of high frequency equipment for health treatments in Rehabilitation Services at Hospitals is very common, and an important proportion of the sanitary personnel assigned to the mentioned Service is exposed to radio frequencies and microwaves emitted by this equipment. We present the results of the measurements and assess of the possible dangers related to the exposure in a Hospital located in Sant Cugat del Vallès (Barcelona). We carried out the measurements by the end of November The meters used for the measurement of the nonionizing radiations were the following: - Narda model 8718 (serial nr ), with the sensor 8762D (serial nr ) for measurement of the electric field and the sensor 8733D (serial nr ) for the 1

2 measurement of the magnetic field. The last calibration was made on the 05 of January Wandel model EMR-300 (nº of series AI-0050), with the shaped sensor type 26 (serial nr. F0003) for the measurement of the electric field and the sensor type 12 (serial nr. R0017) for the measurement of the magnetic field. The last calibration was made on the 11 of December The electromagnetic emissions have been estimated for two emitting machines that are very common in Rehabilitation Services: The short wave (emission at MHz) and the microwave (2.45 GHz). The characteristics of these machines, as well as the way of operation (linked to some usual health treatments) are detailed next: - Short wave equipment (27.12 MHz) of Enraf-Nonius type Curapuls 419 with a coil head or drum. The way of operation selected for the study was a pulsating emission of 82 Hertz with the intensity display at 8. - Microwave equipment (2.45 GHz) of Enraf-Nonius (Dimeq) type Radarmed with a broad field head. The way of operation selected for the study was a continuous emission with the dose display at 99. Although good practices (as well as instructions that operators receive from their supervisors) imply to leave the equipment as soon as the radiation starts, it has been observed that giving instructions and explanations to patients during treatment is usual, both at the position of the operator of the high frequency equipment or along the stretcher where the patient sits o lays down. 2 This habit implies that exposures of sanitary workers last unnecessarily, and that sometimes reach the 15 minutes of usual duration of treatment. These long exposures, that correspond to the worst case, occur with enough frequency and can be considered representative for the bad practices. For the measurement and assessment we have considered what has been said in the previous paragraph, and we carried out measurements of 6 minutes, in agreement with what has been established in the norm of reference (ICNIRP 98: Effective values rms are obtained for 6 minutes), although in suitable conditions of use the exposure is clearly under 6 minutes. 3 The measurements were made with the aid of a dielectric tripod in order to obtain the undisturbed field, avoiding interferences with the electric field from the technician who handles the sensor. The measurements made for the short wave equipment correspond to the next field zone (wave length =11 meters), and this is the reason why we must separately estimate the electric field and the magnetic field. Nevertheless, the results obtained for the electric field generated by the Curapuls with a coil head were very low, and so those measurements are not included in this communication. The measurements made for the microwave equipment correspond to far field zone (wave length =12 centimeters), and this is the reason why with a single measurement, in our case of electric field, the radiation is sufficiently assessed (behavior of a flat wave in a free field). The measurements results appear in the following tables. A simple statistical treatment of the results is made in order to draw conclusions (it assumes that the 7 obtained values are distributed according to a lognormal law). For each radiating machine we pretend: - To know the field s value in the position of the worker when the equipment is operated. - To compare the values obtained by both meters with their different sensors 2

3 Short Wave Equipment Curapuls 419 (27,12 MHz) Magnetic Field Measurements 4 Narda sensor 8733D Wandel EMR sensor type 12 Measurements Results Measurements Results 1 0,0168 A/m 1 0,0159 A/m 2 0,0254 A/m 2 0,0163 A/m 3 0,0132 A/m 3 0,0167 A/m 4 0,0208 A/m 4 0,0164 A/m 5 0,0187 A/m 5 0,0153 A/m 6 0,0266 A/m 6 0,0148 A/m 7 0,0198 A/m 7 0,0171 A/m Geomet. Mean 0,0197 Geomet. Mean 0,0160 Geom. Std. Dev. 1,2715 Geom. Std. Dev. 1,0517 Mathematical espec.(me) 0,0203 Mathematical espec.(me) 0,0160 Upper C.L. (Me) 0,0242 Upper C.L. (Me) 0,0166 Lower C.L. (Me) 0,0170 Lower C.L. (Me) 0,0155 Microwave Equipment Radarmed (2,45 GHz) Electric Field Measurements Narda sensor 8762D Wandel EMR Sensor type 26 Measurements Results Measurements Results 1 34,89 V/m 1 24,536 V/m 2 33,41 V/m 2 24,509 V/m 3 32,43 V/m 3 22,331 V/m 4 33,48 V/m 4 26,852 V/m 5 37,94 V/m 5 23,796 V/m 6 31,56 V/m 6 22,728 V/m 7 32,66 V/m 7 21,536 V/m Geomet. Mean 33,712 Geomet. Mean 23,700 Geom. Std. Dev. 1,0626 Geom. Std. Dev. 1,0762 Mathematical espec.(me) 33,775 Mathematical espec.(me) 23,764 Upper C.L. (Me) 35,315 Upper C.L. (Me) 25,082 Lower C.L. (Me) 32,301 Lower C.L. (Me) 22,515 In addition to the previous results, a series of additional measurements were carried out to observe the decreasing of the field related to the distance from the emitting machine. For it, 10 measurements were made, each of them further away from the previous along the axis of the stretcher, this time with a single meter, the Wandel EMR-300, and when a tendency of diminution of the field was observed, it was represented mathematically. The results were: Short Wave Equipment Curapuls 419 (27,12 MHz) Magnetic Field Measurements 3

4 Wandel EMR Sensor type 12 Measurements Distance to Radiating machine Results (A/m) (cm) , , , , , , , , , ,0036 The statistical linear fit corresponding to the 10 measured points is not given since these values followed a erratic tendency and could not be satisfactorily represented. Microwave Equipment Radarmed (2,45 GHz) Electric Field Measurements Wandel EMR Sensor type 26 Measurements Distance to Radiating machine Results (%) (cm) , , , , , , , , , , ,3 The statistical linear fit of the electric field related to the inverse of the distance to de radiating machine Electric field % Decrease of electric field value related to 1/r y = 1156,8x - 2,5415 R 2 = 0, ,005 0,01 0,015 1/r (cm) 4

5 The previous chart shows that the level of electric field decreases by a factor 1/r, being r the distance between the radiating machine and the meter. It is considered that the sanitary workers that use such high frequency radiating machines are professionally exposed, and for that reason all of them have received the information and suitable training so as to work with non- ionizing radiations. The standards used to assess the exposure for the professionally exposed workers to non-ionizing radiations are the established by the ICNIRP in their guidelines (year 1998, for frequencies from 0 Hz up to 300 GHz). The limits (reference levels for electric fields and magnetic fields) set by ICNIRP98 that are being used in this study are: ICNIRP 98 Guidelines for limiting exposure (occupational) Magnetic field limit for MHz (rms value): 0.16 A/m Electric field limit for 2.45 GHz (rms value): 137 V/m CONCLUSIONS Conclusions of this study will take into account the following points: - The values obtained for magnetic field in the usual position of the sanitary worker for the Curapuls short wave machine are 10 times lower that the reference level established by the ICNIRP. - The values obtained for electric field in the usual position of the sanitary worker for the Radarmed microwave machine are 5 times lower that the reference level established by the ICNIRP - We can affirm that the probability given to surpass the mentioned reference levels or limits is practically non-existent. - The results given by the meter Narda 8718 are between 20 and 30 % above the values given by the other meter, the Wandel EMR The decreasing of the electric field is inversely proportional to the distance from the radiating machine (1/r) in far field zone (behavior of flat wave in free field) - The decreasing of the magnetic field related to the distance also takes place in a next field zone, but through a random or erratic form, and we have not been able to represent this decrease by means of a mathematical model In spite of having verified that in the usual positions of workers is almost impossible to exceed the established limits, it is advisable to mention some recommendations in order to diminish the exposure of the sanitary workers to non-ionizing radiations: - To minimize the exposure times to those necessary, avoiding to give unnecessary instructions or to chat with the patient when the equipment is radiating. - To maximize the distance to the radiating machine, considering that the smaller the distance is, the higher the field value rises. Carry in mind the philosophy ALARA (As Low As Reasonably Achievable) - To inform and to train the exposed workers so that they know the risks that carry some bad habits and are able to detect the symptoms of possible damages for their health caused by this type of radiations. - To check regularly the high frequency machines, with the purpose of avoiding possible damages that may generate unusal high radiations. - To take additional precautions if some of the exposed workers wears active implants (pacemaker, for example) or uses metallic prosthesis. 5,6 5

6 REFERENCES 1. ICNIRP98. Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz) (1998) 2. Radiaciones no ionizantes. Prevención de riesgos. INSHT (1988) 3. Area de Higiene de Agentes Físicos. Dirección Seguridad e Higiene de ASEPEYO. Seguridad y Salud frente a Emisiones Electromagnéticas. Monografías de Seguridad e Higiene (2002) 4. S. Huertas Ríos Evaluación estadísica de los resultados de las mediciones y muestreos. (2003) 5. Campos Electromagnéticos y Salud Pública Comité Expertos. Subdirección General de Sanidad Ambiental y Salud Laboral. Ministerio de Sanidad y Consumo (2001) 6. Pere J. Riu Efectes dels camps electromagnètics en els éssers vius CREB (1999) 6