Oct 3, 2011
Induction cookers: is EMF an issue?
Domestic induction cookers use electromagnetic fields (EMFs) with frequencies between 20 and 100 kHz to heat saucepans that are placed on the cooking surface. Although all products on the market comply with multiple restrictions governing human exposure to EMFs, a team from Slovenia has published details of a study considering the levels that pregnant women and young children could find themselves exposed to (Phys. Med. Biol. 56 6149).
"Induction cookers are becoming ever more popular and we were unable to find much relevant data regarding human exposure to any kind of sources in this frequency range," researcher Bor Kos, from the Laboratory of Biocybernetics at the University of Ljubljana, told medicalphysicsweb. "To our knowledge, our study is the first to investigate the distribution of induced currents and electric fields in non-homogeneous anatomically correct human models exposed to EMF in the near field of induction cookers."
Induction cookers 101
The increasing popularity of induction cookers can be put down to a range of benefits, including faster cooking times and energy efficiency. Induction cookers use magnetic fields to induce an electric current in the ferromagnetic base of the saucepan, which in turn heats the vessel. Although this is effectively a closed loop and the majority of the magnetic field lines go through the base of the pot, some stray fields are inevitable. These do, however, decrease rapidly with distance from the cooker.
When it comes to testing the emissions from induction cookers, the procedure in the current European standard (EN) specifies that measurements should be performed 30 cm from the front of the cooker. "In the case of pregnant women, when the lady stands in front of the cooker, the foetus is particularly close to the source of the magnetic field," said Kos. "The head and central nervous system of any child standing next to the cooker are also in close proximity to the source. Therefore, we deemed it necessary to investigate how such use could affect the compliance with safety standards."
Making the measurements
Kos and his colleagues measured the magnetic flux density (B) at 30 cm from the front of the induction cooker, as well as at distances of 1, 5 and 10 cm. Measurements were also taken at various vertical distances relative to the level of the cooking surface, which was 85 cm from the ground. All of these data were then applied to a numerical model in order to calculate the induced electric field (E) and induced current (J) in 26- and 30-week pregnant women, and 6- and 11- year old children.
In all cases, the calculated values of E and J fell below the basic restrictions published in the guidelines, as one would expect from any electrical appliance on the market. However, the team found that the pot size used with respect to the size of the cooking area had a strong effect on the stray magnetic fields. Placing pots with diameters of 15, 20 and 25 cm on the same 21 cm cooking ring resulted in magnetic fields of 4.5, 2.4 and 0.9 µT respectively – a significant variation.
"Usually the manufacturers specify a minimum diameter for each cooking ring, however, consumers are not always aware of these recommendations," commented Kos. "Induction cookers don't exceed any basic restrictions but in the case of inappropriate cooking vessels, that may not necessarily be true. It essential that users follow the manufacturers' recommendations regarding proper cooking vessels, or in the absence of such recommendations, use cooking vessels that completely cover the cooking ring."
• Related articles in PMB
Pre- and post-natal exposure of children to EMF generated by domestic induction cookers
Bor Kos et al Phys. Med. Biol. 56 6149
Dielectric properties of human placenta, umbilical cord and amniotic fluid A Peyman et al Phys. Med. Biol. 56 N93
The Virtual Family—development of surface-based anatomical models of two adults and two children for dosimetric simulations Andreas Christ et al Phys. Med. Biol. 55 N23
Electrical conductivity of tissue at frequencies below 1 MHz
C Gabriel et al Phys. Med. Biol. 54 4863
About the author
Jacqueline Hewett is a freelance science and technology journalist based in Bristol, UK.