Reviewed: March 2022
The Electric and Magnetic Field Safety Program at the University of Toronto
Introduction
Static electric and magnetic fields, as well as variable electromagnetic fields are used extensively at the University of Toronto, primarily for research and in telecommunication.
The University of Toronto is committed to ensuring that the use of static electric and magnetic fields and variable electromagnetic fields at the University is carried out in a safe manner with due regard for employees, students, the public and the environment. The University of Toronto Radiation Protection Authority (UTRPA) is charged with ensuring the existence of effective radiation safety programs for each type of radiation. The Radiation Protection Service is charged with the administration of the radiation safety programs.
Health Effects
1. Static Magnetic and Electric Fields
In a workplace environment with static magnetic fields above 2 T (Tesla), rapid motions can create transient sensory effects. Metallic objects in higher fields can create a projectile hazard. Workers with implanted ferromagnetic or electronic medical devices can suffer from interferences with magnetic fields above 0.5 mT (milliTesla) [1; 2].
Strong static electric fields can create spark discharges in the vicinity of conductors or contact currents that can lead to electrocution. Ungrounded objects can acquire electrical charges if located in strong static electric fields and can also create contact currents.
There are no proven health effects of static electric and magnetic fields with values under the limits in Table 1.
CAUTION: Strong magnetic fields can erase magnetic media, disable ABM and credit cards, and damage some watches.
2. Time Varying Electric and Magnetic Fields (EMF) in the Extremely Low Frequency (ELF) Range (1 Hz to 3 Hz
a. Acute Effects
Acute effects of exposure to extremely low frequency (ELF) EMFs on the nervous system are the direct stimulation of nerve and muscle tissue and the induction of retinal phosphenes. There is also strong indirect scientific evidence that the Central Nervous System (CNS) functions, such as cognitive processing, can be affected by induced electric fields below the threshold for direct stimulation. In addition, painful currents can occur when a person makes contact with a conducting object at a different electrical potential. All these effects have thresholds, below which they do not occur. The adverse effects can be avoided by meeting appropriate basic restrictions on induced electric fields in the body and on contact current.
Strong electric fields in this frequency range can produce a wide range of safety hazards like spark discharges and contact currents from ungrounded conductors. Prudence shall be taken when handling flammable materials (possible combustion and ignition), or electro-explosive devices (explosion) in strong electric fields.
b. Chronic Effects
ELF magnetic fields were classified in 2002 by the World Health Organization in category 2B as “possibly carcinogenic to humans” This category is used for agents, mixtures and exposure circumstances for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. The basis for this classification was the epidemiologic results in some studies on childhood leukemia. In the same category 2B (possibly carcinogenic to humans) is coffee. Coffee may increase the risk of kidney cancer while at the same time being protective against bowel cancer.
3. EMF in Radiofrequency (RF) and microwave Range (3 kHz to 300 GHz)
a. Acute Effects
The most consistent effects of acute RF and microwave exposure on humans are the thermoregulatory responses of the cardiovascular system to RF-induced heating, increasing heat loss from the skin through increased skin blood flow and evaporative heat loss from sweat.
Most recent studies [3] of human subjects, including adults, children, and adolescents, have focused on the possible effects of essentially non-thermal exposures to mobile phone-type RF, often simulating mobile phone use and so only involving localized exposure of part of the head. Several non-thermal interaction mechanisms have been proposed but to date, none have been experimentally confirmed. A wide range of subjective symptoms including headaches and migraine, fatigue, and skin itches have been attributed to various RF sources both in the home and the workplace. However, the evidence from double-blind provocation studies suggests that the reported symptoms are not causally related to EMF exposure.
Thermally significant RF exposure can impair male fertility and cause increased embryo and fetal losses and increase the incidence of fetal malformations and anomalies. Such effects have not been consistently shown at exposure levels that do not induce temperature elevation of 1°C or more. The studies that have addressed postnatal developmental indices or behaviour after prenatal exposure to low-level RF radiation have generally reported a lack of effects. Effects resulting from long-term exposure during the development of juvenile animals have been addressed in only a few studies, and the data are insufficient for conclusions. Cataracts in the eyes of anesthetized rabbits remain a well-established thermal effect of RF exposure. However, primates appear to be less susceptible to cataract induction than rabbits, and opacities have not been observed in primates following either acute or prolonged exposures.
b. Chronic Effects
Concerning cancer-related effects, the recent in vitro and animal genotoxicity and carcinogenicity studies are rather consistent overall and indicate that such effects are unlikely at specific absorption rate (SAR) levels up to 4 W kg-1 [4; 5]. Concerning in vitro studies of RF effects on non-genotoxic end-points such as cell signaling and gene/protein expression, the results are more equivocal, but the magnitudes of the reported RF radiation-induced changes are very small.
Health Canada considers that: ”At present, there is no scientific basis for the premise of chronic and/or cumulative health risks from RF energy at levels below the limits outlined in Safety Code 6. Proposed effects from RF energy exposures in the frequency range between 3 kHz and 300 GHz, at levels below the threshold to produce thermal effects, have been reviewed. At present, these effects have not been scientifically established, nor are their implications for human health sufficiently well understood. Additionally, a lack of evidence of causality, biological plausibility and reproducibility greatly weaken the support for the hypothesis for such effects. Thus, these proposed outcomes do not provide a credible foundation for making science-based recommendations for limiting human exposures to low-intensity RF energy.” [5]
University of Toronto limits for exposure to Static Electric and Magnetic Fields
In Canada, there are no established limits for static electric and magnetic fields. The Ontario Ministry of Labour uses the American Conference of Governmental Industrial Hygienists (ACGIH) limits [2]. These limits are presented in Table 1. It should be mentioned that these limits are similar to the limits recommended by the International Commission of Non-Ionizing Radiation Protection (ICNIRP) [1].
| Useful Conversions |
| 1 T (Tesla) = 10,000 G (Gauss) |
| 1 mT (milliTesla) = 0.001 T (Tesla) |
| 1 μT (microTesla) = 0.000001 T (Tesla) |
Table 1 – Static Electric and Magnetic Field Limits
| Exposure | Ceiling Value |
| Whole body (general workplace) [2] | Magnetic field 2 T (20,000 Gs) |
| Whole body (special worker training and controlled workplace environment) [2] | Magnetic field 8 T (80,000 Gs) |
| Limbs [2] | Magnetic field 20 T (200,000 Gs) |
| Medical device wearers [2] | Magnetic field 0.5 mT (5 Gs) |
| General Public – exposure to any part of the body [1] | Magnetic field 400 mT (4000 Gs) |
| Electric field in air (occupational exposure) [2] | Electric field 25,000 V/m |
| Contact currents from touching ungrounded objects that acquired electric charge in a strong static electric field [2] | Electric current 1 mA |
Intervention levels at the University of Toronto are established at 1/2 of the values from table 1, except for medical device wearers. The limits for the static magnetic field for medical device wearers remain at 0.5 mT unless specified by the medical doctor who approved the implementation of the medical device.
University of Toronto Limits for Exposure to Sub-radio Frequency EMFs (1 Hz to 3 kHz)
For EMF with frequencies from 1 Hz to 3 kHz, the University of Toronto will apply the limits recommended by ICNIRP. There are very small differences between ICNIRP and ACGIH limits. The ICNIRP limits are presented in tables 2, 3 and 4.
Table 2 – EMF Limits in the Range from 1 Hz to 3 kHz – Occupational [3]
| B magnetic field density | ||||
| Frequency range | E electric field strength (V/m) | H magnetic field strength (A/m) | T | Gs |
| 1- 8 Hz | 20000 | 1.63 x 105 / f 2 | 0.2 / f 2 | 2 x 103 / f 2 |
| 8 – 25 Hz | 20000 | 2 x 104 / f | 2.5 x 10-2 / f | 2.5 x 102 / f |
| 25 – 300 Hz | 500000 / f | 800 | 10-3 | 10 |
| 60 Hz | 8333 | 800 | 10-3 | 10 |
| 300 Hz – 3 kHz | 500000 / f | 2.4 x 105 / f | 0.3 / f | 3000 / f |
f is the frequency Hz
Table 3 – EMF Limits in the Range from 1 Hz to 3 kHz – General Public [3]
| B magnetic field density | ||||
| Frequency range | E electric field strength (V/m) | H magnetic field strength (A/m) | T | mGs |
| 1- 8 Hz | 5000 | 3.2 x 104 / f 2 | 4 x 10-2 / f 2 | 4 x 102 / f 2 |
| 8 – 25 Hz | 5000 | 4 x 103 / f | 5 x 10-3 / f | 50 / f |
| 25 – 50 Hz | 5000 | 160 | 2 x 10-4 | 2 |
| 50 – 400 Hz | 250000 / f | 160 | 2 x 10-4 | 2 |
| 60 Hz | 4166 | 160 | 2 x 10-4 | 2 |
| 400 Hz – 3 kHz | 250000 / f | 6.4 x 104 / f | 8 x 10-2 / f | 800 / f |
f is the frequency Hz
Table 4 – Reference Levels for Time Varying Contact Currents from Conductive Objects from 1 Hz to 3 kHz [3]
| Exposure characteristics | Frequency range | Maximum contact current (mA) |
| Occupational | up to 2.5 kHz | 1.0 |
| 2.5 – 3 kHz | 0.4 x f | |
| General public | up to 2.5 kHz | 0.5 |
| 2.5 – 3 kHz | 0.2 x f |
f is the frequency in kHz
Intervention levels at the University of Toronto are established at 1/2 of the values from tables 2, 3 and 4.
University of Toronto Limits for Exposure to Radiofrequency (RF) and Microwave EMFs (3 kHz to 300 GHz)
The limits recommended by Canada Safety Code 6 will be applied at the University of Toronto in this frequency range. Two international ICNIPR standards also cover this wavelength range, 3 kHz and 100 kHz [3] and 100 kHz to 300 kHz [6]. They are presented in tables 5, 6, 7 and 8.
Table 5 – Induced Current Reference Levels [5]
| Frequency (MHz) | Reference level basis | Reference level (IRL) through a single foot (mA, root mean square) |
Reference period | |
| Public | Occupational | |||
| 0.003 – 0.4 | Nerve stimulation | 100 f | 225 f | Instantaneous* |
| 0.4 – 110 | Specific absorption rate | 40 | 90 | 6 minutes** |
f is frequency measured in MHz
Table 6 – Contact Current Reference Levels [5]
| Frequency (MHz) | Reference level basis | Reference level (IRL) through a single foot (mA, root mean square)> |
Reference period | |
| Public | Occupational | |||
| 0.003 – 0.1 | Nerve stimulation | 200 f | 400 f | Instantaneous* |
| 0.1 – 10 | Specific absorption rate | 20 | 40 | Instantaneous* |
| 10 – 110 | Specific absorption rate | 20 | 40 | 6 minutes** |
f is frequency measured in MHz
* At no point in time shall the root mean square (RMS) values for induced and contact currents exceed the reference levels with an instantaneous reference period in Tables 5 and 6. In the case of currents with amplitude modulation, the RMS value during the maximum of the modulation envelope shall be compared to the reference level.
** For exposures shorter than the reference period, currents may exceed the reference levels, provided that the time average of the squared value of the current over any time period equal to the reference period shall not exceed IRL. For exposures longer than the reference period, including indefinite exposures, the time average of the squared value of the current over any time period equal to the reference period shall not exceed IRL.
Table 7 – Exposure Limits for Uncontrolled (Public Areas) Environments from 3 kHz to 300 GHz [5]
| Frequency (MHz) | Electric field strength (V/m) | Magnetic field strength (A/m) | Power density (W/m2) | Average time (min) |
| 0.003 – 1 | 83 | 90 | Instantaneous | |
| 1 – 10 (nerve stimulation) |
83 | 90 | Instantaneous | |
| 1 – 10 (specific absorption rate) |
87 / f 0.5 | 0.73 / f | 6 | |
| 10 – 20 | 27.46 | 0.0728 | 2 | 6 |
| 20 – 48 | 58.07 / f 0.25 | 0.1540 / f 0.25 | 8.944 / f 0.5 | 6 |
| 48 – 300 | 22.06 | 0.05852 | 1.291 | 6 |
| 300 – 6000 | 3.142 f 0.3417 | 0.008335 f 0.3417 | 0.02619 f 0.6834 | 6 |
| 6000 – 15000 | 61.4 | 0.163 | 10 | 6 |
| 15000 – 150000 | 61.4 | 0.163 | 10 | 616000 / f 1.2 |
| 150000 – 300000 | 0.158 f 0.5 | 4.21 x 10-4 f 0.5 | 6.67 x 10-5 f | 616000 / f 1.2 |
f is frequency measured in MHz
Table 8 – Exposure Limits for Controlled Environments from 3 kHz to 300 GHz [5]
| Frequency (MHz) | Electric field strength (V/m) | Magnetic field strength (A/m) | Power density (W/m2) | Average time (min) |
| 0.003 – 1 | 170 | 180 | Instantaneous | |
| 1 – 10 (nerve stimulation) |
170 | 180 | Instantaneous | |
| 1 – 10 (specific absorption rate) |
193 / f 0.5 | 1.6 / f | 6 | |
| 10 – 20 | 61.4 | 0.163 | 10 | 6 |
| 20 – 48 | 129.8 / f 0.25 | 0.13444 / f 0.25 | 44.72 / f 0.5 | 6 |
| 48 – 300 | 49.33 | 0.1309 | 6.455 | 6 |
| 300 – 6000 | 15.60 f 0.25 | 0.04138 f 0.25 | 0.6455 f 0.5 | 6 |
| 6000 – 15000 | 137 | 0.364 | 50 | 6 |
| 15000 – 150000 | 137 | 0.364 | 50 | 616000 / f 1.2 |
| 150000 – 300000 | 0.354 f 0.5 | 9.40 x 10-4 f 0.5 | 3.33 x 10-4 f | 616000 / f 1.2 |
f is frequency measured in MHz
Intervention levels at the University of Toronto are established at 1/2 of the values in tables 5, 6, 7 and 8.
Controls
a. Hazard identification
Generally, a safety factor of 10 was introduced in calculating the limits presented in tables 1 to 8, however, these are considered ceiling values and should never be reached.
The supervisors will receive training in identifying EMF hazards. Examples of devices that can produce electric and magnetic fields above the limits are presented in Appendix A. When new equipment producing large EMFs is bought or manufactured, and installed in a University of Toronto controlled area the Radiation Protection Service must be informed.
The supervisors of workplaces in all areas controlled by the University of Toronto with fields possible at levels above the University of Toronto intervention limits shall contact the Radiation Protection Service (RPS). The RPS will perform measurements to identify the high field areas and compare the results with values from tables 1 to 7. All areas where measured values are above the intervention levels will be considered controlled areas. Controlled areas will be marked with appropriate warning signs for the electric or magnetic field, and access will be restricted to trained personnel.
b. Warning signs and access controls
All rooms, areas, enclosures with magnetic fields density above 0.5 mT will have a sign indicating restricted access for persons with implanted medical devices that may be interfered with by a magnetic field. Examples of these signs are presented in Appendix B – Electric and magnetic field warning signs.
All rooms, areas, and enclosures with values of electric and/or magnetic fields above the University of Toronto intervention levels will be marked with similar signs to the ones presented in Appendix B.
All rooms, areas, and enclosures with values of electric and magnetic fields above the University of Toronto intervention levels will be secured to prevent unauthorized access. This can be achieved with walls, doors, barriers, fences, etc.
c. Training
All persons with access to the EMF controlled areas will receive training covering: EMF hazards identification, health effects, signs, engineering control measures, operating procedures.
Periodic refresher training will be delivered. The refresher training will cover changes in the regulations and in the University of Toronto EMF safety program, changes in work procedures, etc.
d. Personal Protective Equipment (PPE)
Tools used in magnetic fields above the intervention levels will be made of non-magnetic materials.
If a person needs to perform work in an area that may have values close to the values from tables 1 to 8, the person shall wear personal protective equipment and a field warning instrument with the visible and audio signal.
e. Workplace inspections
Workplace inspections and EMF measurements are performed when there is a concern that students, faculty, staff or the public can be exposed above the University’s intervention levels. New equipment or devices that can produce high levels of EMFs will be inspected by the HSO before the equipment or device is used. Areas found with EMF levels above the University’s intervention levels will be marked and public access will be controlled.
In performing a workplace inspection involving EMF hazards, the check sheet in Appendix C will be used.
Appendix A – Example of Equipment and Devices that can Produce EMFs at the University of Toronto
| Source | Frequency | Potential for Over-exposure |
| Nuclear Magnetic Resonance Facilities | Static and hundreds of MHz | Yes |
| Power Plant | 60 Hz | Yes |
| Transformers | 60 Hz | Yes |
| Laboratory EMF Generators | 13.56 MHz | Yes |
| Video Display Terminal (VDT) | 0.015 – 03 MHz | No |
| Dielectric Heater | 1 – 100 (typically 27.12) MHz | Yes |
| Diathermy Applicator | 13.56; 27.12; 915; 2,450 MHz | Yes |
| Communications Transmitters: FM Radio | 88 – 108 MHz | Yes |
| Communications Transmitters: VHF TV | 54 – 72; 76 – 88; 174 – 216 MHz | Yes |
| Communications Transmitters: UHF Radio | 470 – 890 MHz | Yes |
| Communications Transmitters: Dish Antenna | 800 – 15,000 MHz | Yes |
| WiFi antenna for LAN – cellular coverage | 2.4 – 5 GHz | Yes |
| Cordless Telephone | 16 – 5,800 MHz | No |
| Cellular Telephone | 824 – 850; 900; 1,800; 1,900 MHz | No |
| Microwave Oven | 915 and 2,450 MHz | No* |
*Federal legislation requires that microwave ovens be constructed to meet stringent microwave leakage limits and to have safety interlocks. When these interlocks are defeated, for example, during repair work, there is a risk of overexposure to microwave radiation.
Appendix B – Warning Signs
Appendix C – Inspection Checklist for EMF Safety
Checklist for workplaces with high electric and magnetic fields.
Required for laboratories with equipment that can produce electric or magnetic fields above the limits specified below at any accessible point.
| Y | N | N/A | |
| Static magnetic or electric field | |||
| Sign on the door indicating “Danger Magnetic or Electric Field Hazard” | |||
| A line on the floor around the equipment indicating H = 400 A/m (B = 0.5 mT) | |||
| No person wearing pacemaker allowed in the marked region | |||
| Visitors are informed that credit cards, analog watches can be affected | |||
| Second line on the floor around the equipment indicating H = 40 kA/m (50 mT) | |||
| No person wearing ferrous implants allowed in the second marked region | |||
| No ferrous object aloud in the second marked region | |||
| A line on the floor around the equipment indicating E = 10,000 V/m | |||
| No person without protection allowed in the marked region | |||
| Sub-radio frequency 1 Hz-3 kHz electromagnetic field (EMF) | |||
| Sign on the door indicating EMF Hazard | |||
| Access control in area above the University of Toronto intervention level | |||
| No person without protective equipment allowed in the region with electric, magnetic or induced currents above occupational limits | |||
| Radiofrequency (RF) and microwave EMF (3 kHz – 300 GHz) | |||
| Sign on the door indicating EMF Hazard | |||
| Access control in area above the University of Toronto intervention level | |||
| No person without protective equipment allowed in the region with electric, magnetic or induced currents above occupational limits | |||
Appendix D – Installing New Antennas Inside the U of T Buildings
The purpose of installing new antennas inside the U of T buildings is to ensure better cellular coverage in different areas of the buildings. Usually, the antennas installed inside the buildings are omnidirectional.
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Typical omnidirectional antennas are shown above.
These antennas have an Electro-Magnetic Field distribution as shown below:
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The power of these antennas is in the range of tens to hundreds of milliwatts. The field intensity reaches the U of T intervention level (10 % of the public limit exposure) at less than 25 cm from the antenna. At a distance above 25 cm from the antenna, the EMF poses no risk to the health and safety of students, staff, faculty or the public.
The installation of new antennas must follow this procedure:
- The company proposing the project will perform the Canada Safety Code 6 analysis. This analysis will take into account all current EMF produced by the antenna already existing inside and outside the building, as well as the field intensity produced by the proposed new antenna system;
- The U of T Radiation Protection Service will verify the Canada Safety Code 6 analysis;
- The application for the project is approved by the U of T Radiation Protection Service;
- After the installation of new antennas, the U of T Radiation Protection Service will perform measurements to confirm the field intensities predicted by the Canada Safety Code 6 analysis.
Appendix E – Installing New Antennas On Top of the U of T Buildings or on Towers inside U of T Controlled Areas
The purpose of installing new antennas on top of the U of T buildings or towers is to ensure better cellular coverage in different areas of the campus. Usually, these antennas are unidirectional.
A typical directional antenna is shown above.
These antennas have an Electro-Magnetic Field distribution as shown below:
|
Horizontal field distribution |
Vertical field distribution |
The power of these antennas is in the range of tens of watts. They are installed on the roofs of buildings or towers. Typical will be 3 antennas at 120° from each other to cover a maximum area. When they are installed on the roofs, the orientation of the main lob of the antenna is towards the outside of the building. They are installed as close as possible to the roof’s edges to ensure the best coverage.
The maximum danger is in front of the antenna. As can be seen from the horizontal and vertical field distributions, the field behind and below the antenna is extremely low. The field on a line perpendicular to the main lob can also reach levels above the U of T intervention value. This field decreases under the U of T intervention level at a distance of less than 2 m.
At a distance greater than 2 m from the antenna (behind, below or on a line perpendicular to the main lob), the EMF poses no risk to the health and safety of students, staff, faculty or the public. Since the antennas are installed close to the edge of the building, keeping a 2 m distance from the edge of the building (as is required by the working at heights procedure), will ensure that persons are not exposed to EMF radiation above the U of T intervention level.
Because of the possibility of the field being above the U of T intervention level, access to the roofs or the towers must be controlled.
On all doors accessing the roofs where antennas are installed, a sign must be posted indicating that at a distance under 2 m from the antennas the electromagnetic field is above the U of T intervention level. Persons accessing the roofs must keep a 2 m distance from the antennas.
All workers who need to go closer to the edge of the building must receive the “working at heights safety training” and avoid being in front of the antenna at all times.
The installation of new antennas must follow this procedure:
- The company proposing the project will perform the Canada Safety Code 6 analysis. This analysis will take into account all current EMF produced by the antenna already existing inside and outside the building, as well as the field intensity produced by the proposed new antenna system;
- The U of T Radiation Protection Service will verify the Canada Safety Code 6 analysis;
- The application for the project is approved by the U of T Radiation Protection Service;
- After the installation of new antennas, the U of T Radiation Protection Service will perform measurements to confirm the field intensities predicted by the Canada Safety Code 6 analysis.
References
- Guidelines on Limits of Exposure to Static Magnetic Fields. International Commission on Non-Ionizing Radiation Protection. 4, 2009, Health Physics, Vol. 96, pp. 504-514.
- American Conference of Governmental Industrial Hygienists: ACGIH. 2009 TLVs and BEIs: Threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati: American Conference of Governmental Industrial Hygienists, 2009.
- Guidelines for Limiting Exposure to Time-Varying Electric and Magnetic Fields (1 Hz to 100 kHz). ICNIRP. 6, 2010, Health physics, Vol. 99, pp. 818-836.
- J, Juutilainen, et al. Exposure to high-frequency electromagnetic fields, biological effects and health consequences (100 kHz – 300 GHz). 2009.
- Health Canada. Limits of Human Exposure to Radiofrequency Electromagnetic Energy in the Frequency Range from 3 kHz to 300 GHz – Safety Code 6. 2015.
- Guidelines for Limiting Exposure to Electromagnetic Fields (100 kHz to 300 GHz). ICNIRP. 5, May 2020, Health Physics, Vol. 118, pp. 483-524.
Contact
| Daniel Cardenas Health & Safety Officer daniel.cardenas@utoronto.ca |