EPFL STI QMAT
Magnets generating intense magnetic fields are common in research.
While older magnets are based on traditional technology (copper coils and water cooling) with moderate fields ranging from 0.1 T to 2 T, the technologies involving superconducting magnets allow reaching static magnetic fields that now exceed 20 T. At the same time there are also large differences in magnetic shielding/ residual fields. Depending on residual field extent, there can be a risk to users and nearby equipment.
The most important effects of the static magnetic field on the human body are:
- Sensory effects: From 2T, effects such as nausea, vertigo and metallic taste in the mouth may appear.
- Electrocardiogram: Above 8T, a reversible modification of the electrocardiogram is possible.
To date, there is no scientific consensus on the long-term effects of low, regular exposure.
The effects of non ionizing, time varying electromagnetic fields (EMF) are similar to those of static magnetic fields with some major differences:
- Visual disturbances: Above 2-3 mT and 20 Hz, some people may experience visual disturbances, characterized by the perception of luminous spots called magnetophosphene.
- Hyperthermia: When exposed to high-frequency fields (greater than 100 kHz), the energy absorbed by biological tissues can lead to hyperthermia characterised by an increase in body temperature.
- Hypersensitivity: Some hypersensitive people may have physical or muscular asthenia or even muscle aches, tiredness, memory loss or abnormal irritability, sleep disorders, headaches.
- Interference with medical devices (MD)
The term medical device (MD) covers: active implanted medical devices, passive implanted medical devices or body worn medical devices. In the presence of the field, MD might heat by induction or move in the body. Active MD might disfunction.
For static magnetic fields, the operation of MD is not adversely affected by fields below 0.5 mT (5 Gauss).
- Risks of ferromagnetic objects becoming projectiles
Loose ferromagnetic object can become projectile in the vicinity of a strong magnet, with possibility to hit/ injure personnel on its way.
The threshold value for attracting ferromagnetic objects by a static magnetic field (> 100 mT) was set to 3 mT.
- Respect the markings/ indicated limits.
- Do not bring ferromagnetic tools and other objects that could be attracted to the sources of the magnetic fields.
Cryogens such as liquid Nitrogen and liquid Helium, which are present in the magnet cryostat and dewars, have the following risks associated with them: asphyxiation, frostbite and overpressure/ explosion. See the page on Cryogenic hazards for more information.
The occupational exposure (42 hours per week, 8 hours a day, for long periods) limit values for chemical and physical agents in Switzerland are given in SUVA’s directive ‘Valeurs limites d’exposition aux postes de travail’, 1903.f.
The limit values for static magnetic fields are:
- 2 T for head and trunk and
- 8 T for exposure to arms and legs.
Pregnant women
The limit value for occupational exposure is 40 mT for pregnant women. If you are concerned, announce your pregnancy (it is confidential) to make sure the limit is respected.
General public exposure limit values
The general public comprises entire population – individuals of all ages and of varying health status, and may include particularly susceptible groups or individuals. In many cases, members of the public are unaware of their exposure to EMF.
These considerations underlie the adoption of more stringent exposure restrictions for the public than for the occupationally exposed population.
Stripes marking and restriction zones at EPFL
At the EPFL, the field values of all eligible instruments are measured by DSE-OHS or evaluated using numerical simulation, technical data or user manual provided by the manufacturer. Based on the measurement and evaluation, the DSE-OHS makes the instrument field cartography.
The cartography made by DSE-OHS is transmitted to DSE-EXPL for the placement of the field marking stripes on the laboratory floor. The values of magnetic flux density of the static fields that are indicated on the floor, and corresponding safety measures and access restrictions are given in the Table below.
| Magnetic flux density, ELV value and description | Description/ Safety measure | Access forbidden to |
|
0.5 mT value used for static magn. fields and EMF with f<= 10 Hz Maximum value authorised for the holders of MD |
– The field indicated on the laboratory door panel or with a chain if it is not a closed space.
– Indicated by a yellow stripe on the laboratory floor
– Staff training mandatory if yellow line is outside the instrument itself, or can be accessed during the experiment in normal use.
– Controlled access and special management of laboratory cleaning if yellow line ⋝ 50 cm from the instrument itself.
|
No access to general public No access to holders of MD |
| 3 mT (30 G) | Possible attraction of small ferromagnetic objects by the field, they can become projectiles. | Any ferromagnetic object |
| 2 T (occupational ELV) |
– Access restriction
– Indicated on the laboratory door panel
– Indicated by the red stripe on the floor
– Training, information
– Health surveillance
|
Only trained and authorised personnel can access, forbidden to all remaining staff. |
| Above ELV |
Interlock, access restriction Warning, information to employees |
All personel |
DSE-OHS provides the online training on non-ionizing EMF risks (in development). This is a mandatory training for all employees accessing the zones marked on the floor.
In order to map the field and place the marking stripes on the floor, please contact OHS before purchasing the instrument generating magnetic field.
The purpose of the announcement of the instrument is twofold:
- DSE-OHS team will help for planning the most adequate place for the instrument installation (e.g. ensure the field lines do not extend into office or common spaces).
- DSE-OHS is responsible for enforcing internal directive and controlling that the ELV are respected and safety measures put in place for each new installation.
Also contact DSE-OHS in case of a change in operation (change of position in a room, change of room, field strength etc.).
Health surveillance is mandatory for the following cases:
- all employees working inside the zone delimited by a red stripe as defined in the Table above
- all employees bearing a MD that will be working with or in vicinity of an instrument producing magnetic field.
If one of the above criteria is met, send an email to: [email protected] to register for medical surveillance.
The OHS service will get in touch with you and organize a medical checkup and a workplace visit whose goal is to make a risk analysis and implement risk control. Pending risk analysis, the exposure must be avoided.