INTERNATIONAL COMMISSION ON NON‐IONIZING RADIATION PROTECTIONICNIRP GUIDELINESON LIMITS OF EXPOSURE TO STATICMAGNETIC FIELDSPUBLISHED IN: HEALTH PHYSICS 96(4):504‐514; 2009

ICNIRP PUBLICATION – 2009

ICNIRP Guidelines

GUIDELINES ON LIMITS OF EXPOSURE TO STATICMAGNETIC FIELDSInternational Commission on Non-Ionizing Radiation Protection*
INTRODUCTION

electric charges, but only when such charges are inmotion. A magnetic field can be represented as a vector
and may be specified in one of two ways: as magnetic
flux density B or as magnetic field strength H. B and H
are expressed in teslas (T) and amperes per meter (Am⫺1), respectively. In a vacuum and with good approximation in air, B and H are related by the expression

THE RAPID development of technologies in industry andmedicine using static magnetic fields has resulted in an
increase in human exposure to these fields and has led toa number of scientific studies of their possible healtheffects. The World Health Organization (WHO) recently
developed a health criteria document on static electricand magnetic fields within the Environmental HealthCriteria Program (WHO 2006). The document contains a
review of biological effects reported from exposure to
static fields and, together with other recent publications[mainly International Commission on Non-Ionizing Radiation Protection (ICNIRP) 2003, McKinlay et al. 2004,
and Noble et al. 2005], serves as the scientific databasefor the development of the rationale for the guidelines
described in the current document, which supersede
those published by ICNIRP in 1994 (ICNIRP 1994).

B⫽␮oH.
(1)
The constant of proportionality ␮o in eqn (1) is termed
the permeability of free space and has the numericalvalue 4␲ ⫻ 10⫺7 expressed in henrys per meter (Hm⫺1). Thus, to describe a magnetic field in air ornonmagnetic materials (including biological materials)
with an adequate approximation, only one of the B or
H quantities needs to be specified.
The magnitude of the force F acting on an electriccharge q moving with a velocity v in a direction perpendicular to a magnetic flux density B is given by theexpression

SCOPE AND PURPOSE
These guidelines apply to occupational and generalpublic exposure to static magnetic fields. The guidelines
do not apply to the exposure of patients undergoing
medical diagnosis or treatment. Detailed consideration ofprotection of patients is given in an ICNIRP statement onprotection of patients undergoing a magnetic resonanceimaging (MRI) examination (ICNIRP 2004; ICNIRP in
preparation).

F⫽q(v ⫻ B).

(2)

The direction of the force (the Lorentz force) is determined from the vector product of the velocity of thecharge and the magnetic flux density and is therefore
always perpendicular to the direction of the flow ofelectric charge. As a result, the interaction of a magnetic
field with electric charge will result in a change ofdirection of the flow of the charge, but never a change invelocity. Static magnetic fields do not deposit energy into
tissues.
The magnetic flux density, measured in teslas, isaccepted as the most relevant quantity for relating tomagnetic field effects. The magnetic flux within a given
area of surface is the product of the area and thecomponent of the magnetic flux density normal to its
surface.
A summary of magnetic field quantities and units isprovided in Table 1.
Standard international (SI) units are the internationally accepted units for expressing quantities in the

QUANTITIES AND UNITS
Whereas electric fields are associated with the presence of electric charge, magnetic fields result from thephysical movement of electric charge (electric current).
Similarly, magnetic fields can exert physical forces on* ICNIRP, c/o BfS – G. Ziegelberger, Ingolstaedter Landstr. 1,
85764 Oberschleissheim, Germany.
For correspondence contact G. Ziegelberger at the above address,
or email at info@icnirp.org.
(Manuscript accepted 4 December 2008)
0017-9078/09/0
Copyright © 2009 Health Physics Society
504

ICNIRP guidelines on limits of exposure to static magnetic fields ● ICNIRP

Table 1. Static magnetic field quantities and corresponding
SI units.
Quantity

SymbolUnit

Current
Current density
Magnetic field strength
Magnetic flux
Magnetic flux density
Permeability
Permeability of free space

I
J
H
⌽
B
␮
␮o

Amperes (A)Amperes per square meter (A m⫺2)
Amperes per meter (A m⫺1)
Weber (Wb or T m2)
Tesla (T)Henrys per meter (H m⫺1)
4␲ ⫻ 10⫺7 H m⫺1

scientific literature. For a more complete list anddiscussion of concepts, quantities, units, and terminology for non-ionizing radiation protection, the reader isreferred to the relevant ICNIRP publication (ICNIRP
2003).
SOURCES OF EXPOSURE
The natural static magnetic field of the Earth is ⬃50
␮T and, depending on the geographic location, varies
from ⬃30 to 70 ␮T. Magnetic flux densities of the orderof 20 ␮T are produced under high direct current transmission lines. In the future there is a potential for
exposure to greater magnetic flux densities due to thedevelopment of new transport technologies. Fast passenger trains based on magnetic levitation produce relatively
high magnetic flux densities close to the motor. However, for both magnetically-levitated trains and conventional electric trains, the fields inside the passenger cabin
are relatively low, below 100 ␮T, but localized magnetic
fields of up to several mT at floor level can result from thepresence of inductors beneath the floor of passenger
coaches (WHO 2006; ICNIRP 2008). Other sources ofstatic magnetic fields in residential and occupational environments include small permanent magnets in magnet clips
and magnetic attachments (such as bags, buttons, magnetic
necklaces and bracelets, magnetic belts, magnetic toys, etc),
which generate local static fields in excess of 0.5 mT.
The highest non-occupational exposure occurs inpatients undergoing a diagnostic examination by magnetic resonance (MR), a technique that is used to obtain
diagnostic information about the body and increasingly
to guide surgical interventions within the body. MR isbased on the phenomenon of nuclear magnetic resonanceand underlies MRI and magnetic resonance spectroscopy(MRS). In MR procedures, magnetic flux densities typically range from 0.15 to 3 T and the exposure is usuallylimited to less than 1 h, but can be a few hours in duration(Gowland 2005). Interventional medical procedures under
direct real-time control by MRI are becoming increasingly
common. These procedures also lead to increased occupational exposure, especially for medical professionals (surgeons, radiologists, nurses, and technicians). During such505

procedures the medical staff may be within the main
magnetic field region for a long period of time, up to a few
hours. Increased staff exposure can also occur in emergency
situations, when the medical professionals have to intervenevery close to the patient. In addition, brief staff exposuresoccur during movement of patients in and out of MR
systems. Finally, staff involved with the manufacture or
maintenance of these MR systems are also occupationally
exposed to high static magnetic fields.
Functional MRI is now widely used in academic andmedical research on human brain function. MR systems
using higher magnetic fields, up to about 10 T, arecurrently used for research in several institutions worldwide, and operate with special approval from a local
institutional review board or equivalent entity. Exposures
can also occur during other medical applications of static
magnetic fields, such as the use of magnets to holdvarious prostheses in place or for magnetic navigation,
where moveable permanent magnets are used to guidethe tip of cardiac catheters; however, these devices
produce only localized fields.
Strong fields are also produced in high-energy
technologies such as thermonuclear reactors, magnetohydrodynamic systems and superconducting generators.
Research facilities that use bubble chambers, particle
accelerators, superconducting spectrometers, and isotope
separation units also have areas with high magnetic flux
density around these devices. Other industries where
exposure to strong magnetic fields occur are those
involving electrolytic processes such as chlorine or
aluminum production, where typical exposures for mostof the working day are a few mT, with peak exposures up
to several tens of mT, and in the manufacture ofpermanent magnets and magnetic materials.
REVIEW OF THE SCIENTIFIC EVIDENCE
Interaction mechanisms
The three established physical mechanisms throughwhich static magnetic fields interact with living matterare magnetic induction, magneto-mechanical, and electronic interactions.
Magnetic induction. This mechanism originates
through the following types of interaction:● Electrodynamic interactions with moving electrolytes:

Static fields exert Lorentz forces on moving ioniccharge carriers and thereby give rise to induced electric fields and currents. This interaction is the basis ofmagnetically-induced potentials associated with flowing blood which have been theoretically analyzed(Kinouchi et al. 1996). These authors suggested thatthe sinoatrial node of the heart that controls cardiac

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pacing may be the region most sensitive to current andcalculate that, for a field of 5 T, the current density inthis region is around 100 mA m⫺2, which is around
10% of the maximum endogenous current from cardiac electrical activity, rising to around 20% for 10 T.
A detailed assessment of the effects of the electricfields on cardiac function using computational models
of cardiac electrophysiology indicated that, while
fields up to 8 T are unlikely to affect the heart rate andrhythm, this would not necessarily be true for higher
fields (Holden 2005).
● Induced electric fields and currents: Time-varying
magnetic fields induce electric currents in living tissues in accordance with Faraday’s law of induction.
Currents may also be induced by movement in a static
magnetic field. In particular, motion along a field
gradient or rotational motion, either in a uniform fieldor in a field gradient, produces a change in flux linkage
which induces an electric current, in contrast to linear
motion of the body within a uniform static field. With
regard to linear movement in a gradient field, themagnitude of the induced currents and associatedelectric fields increases with velocity of the movement
and amplitude of the gradient. Calculations suggestthat such induced electric fields will be substantial
during normal movement around or within fields⬎2–3 T (Crozier and Liu 2005), and may account for
the numerous reports of vertigo and nausea and magnetic phosphenes experienced by patients, volunteers,
and workers moving in such fields (Schenck et al.
1992; Chakeres and de Vocht 2005; de Vocht et al.
2006b). Measurements of in situ surface electric fields
induced by typical human body movements such as
walking or turning in the fringe magnetic fields of awhole-body 3 T MRI scanner gave 0.15, 0.077, and0.015 V m⫺1 for the upper abdomen, head, and acrossthe tongue, respectively (Glover and Bowtell 2008). A
peak electric field of 0.30 V m⫺1 was measured on thechest. Note that the speed of movements was not
specified in this study. For a body moving at a constant
speed of 0.5 m s⫺1 into a 4 T magnet, Crozier and Liu(2005) estimate the maximum induced electric fieldstrength in the body to be approximately 2 V m⫺1,
approximately equal to the apparent threshold for
peripheral nerve stimulation in the frequency range 10
Hz–1 kHz (ICNIRP 1998). It should be noted, however, that frequencies associated with body movement
are likely to be less than 10 Hz, the frequency below
which accommodation decreases the electrical excitability of nerve tissue due to the slow inactivation of
the voltage-gated sodium ion channels (Bezanilla
2000). Head translational and rotational frequencies
during walking, for example, vary between 0.4 – 4 Hz

April 2009, Volume 96, Number 4(Grossman et al. 1988; Pozzo et al. 1990; MacDougalland Moore 2005).
Magneto-mechanical effects
The two types of mechanical effects that a static
magnetic field can exert on biological objects are as
follows:● Magneto-orientation: In a static field, paramagnetic

molecules experience a torque that orients them in aconfiguration that minimizes their free energy within
the field. This effect has also been well studied for
assemblies of diamagnetic macromolecules with differing magnetic susceptibilities along the principal
axes of symmetry. Generally, these forces are considered too small to affect biological material in vivo
because of the very small (⬃10⫺5) values of magnetic
susceptibility (Schenck 2000). However, geomagnetic
field has been implicated in the detection of directionalcues during the orientation and migration of someanimal species (Kirschvink et al. 2001; WHO 2006).
Moreover, strong static magnetic fields (⬎17 T) havebeen shown to induce mitotic apparatus reorientation,i.e., changes to the orientation of the cleavage planesof frog embryos during the first to third cycle (Valles
et al. 2002); and● Magneto-mechanical translation: In the presence of
gradients, static magnetic fields produce a net translational force on both diamagnetic and paramagnetic
materials. The direction of the force is the same as or
opposite to the gradient of the field for paramagnetic
and diamagnetic materials, respectively. The force is
proportional to the product of magnetic flux density(B) and its gradient (dB/dx). The force exerted on
ferromagnetic objects such as metal of high magnetic
susceptibility (⬎1 for iron or certain types of steel)tools poses danger due to their acceleration in strong
magnetic field gradients. For biological material, theforce is as large as the force of gravity when BdB/dx⬎1,000 T2 m⫺1 (WHO 2006). It has been demonstrated
that an 8 T magnet with a gradient of 50 T m⫺1 candecrease the depth of water in a horizontal troughrunning through the magnet, parting the water bypushing it to either end of the trough lying outside themagnet (Ueno and Iwasaka 1994). The effect at 10 T
amounts to a change in pressure from the inside of themagnet to the outside of less than 40 mm of H2O,
which is thought to be insufficient to affect systemic
blood flow in humans (Schenck 2005). However,Ichioka et al. (2000) observed a reduction in skin bloodflow when a static magnetic field of 8 T was applied to
the whole body of rats; the product of magnetic flux
density and field gradient varied from 200 to 400 T2m⫺1 along the rat’s longitudinal body axis.

ICNIRP guidelines on limits of exposure to static magnetic fields ● ICNIRP

Electron spin interactions
Certain metabolic reactions involve an intermediate
state comprising a radical pair, usually in a singlet statewith the spin of one unpaired electron anti-parallel to thespin of the other (Schulten 1982; McLauchlan andSteiner 1991; Grissom 1995; Nagakura et al. 1998; Hore
2005; WHO 2006). These spin-correlated radical pairs
recombine to form reaction products; an applied magnetic field affects the rate and the extent to which theradical pair converts to the triplet state (parallel spins) inwhich recombination is no longer possible. Althoughexperimental evidence for such effects in biochemicalsystems has been reported (Eveson et al. 2000; Liu et al.
2005), their biological significance is not clear at present.
The “radical pair mechanism” has been suggested (Ritz
et al. 2000) as a mechanism by which animals, particularly birds, may use the Earth’s magnetic field as a sourceof navigational information during migration, and there
is some experimental support for this view (Ritz et al.
2004).
IN VIVO AND IN VITRO STUDIES
A large number of studies have been conducted inan effort to detect biological responses to static magnetic
fields ranging in flux densities from the millitesla range
to several teslas. These have been reviewed comprehensively in ICNIRP (2003), McKinlay et al. (2004), Miyakoshi (2005), Noble et al. (2005), and WHO (2006). The
following is a brief summary of the main conclusions.
Laboratory studies with in vitro systems
Different levels of biological organization at a cellular level have been investigated, including cell-freesystems (employing isolated membranes, enzymes orbiochemical reactions) and various cell models (using
both bacteria and mammalian cells). Endpoints studied
included cell orientation, cell growth, cell metabolic
activity, cell membrane physiology, and gene expression.
Positive and negative findings have been reported
for all these endpoints. The observed effects are rather
diverse and were found after exposure to a wide range ofmagnetic flux densities of up to 8 T. Thresholds for someof the effects were reported, but other studies indicatednon-linear responses without clear threshold values.
However, these responses are not well established. The
aforementioned effect on the mitotic apparatus (Valles etal. 2002) represents a more consistent set of evidence; it
confirmed earlier observations made by the same group(Denegre et al. 1998).
With regard to effects on radical-mediated metabolic reactions, the results of studies conducted so far
suggest that there is no strong likelihood of major effects507

of physiological consequence or of long-term mutagenic
effects arising from magnetic-field-induced changes infree radical concentrations or fluxes (Hore 2005).
Only a few studies on genotoxicity have been
performed (Miyakoshi 2005). No genotoxic or epigenetic effects of exposure to static magnetic fields of up
to 9 T have been shown, except for one study withrepair deficient bacterial strains (Zhang et al. 2003).
The studies with combined exposure to mutagens andstatic magnetic fields indicated modification of theeffects of some of the tested mutagens, but there were
no indications of field-dependence.
Overall there is little convincing evidence from
cellular and cell-free models of biologically harmful
effects of exposure to magnetic fields with flux densities
up to several teslas.
Laboratory studies with animals
A large number of animal studies on the effects ofstatic magnetic fields have been conducted (Saunders
2005). The most consistent responses seen in behavioral
studies suggest that the movement of laboratory rodents
in fields of about 4 T and higher may lead to aversive
responses and conditioned avoidance (Weiss et al. 1992;
Nolte et al. 1998; Houpt et al. 2003). Such effects arethought to result from interactions with the vestibular
apparatus (Snyder et al. 2000). At field levels of the orderof 2 T and lower, however, there is little convincing
evidence from laboratory studies for effects of exposureon learning or on conditioned and unconditioned behavioral responses to a variety of stimuli (Trzeciak et al.
1993). Consistent with this finding, experimental studies
on the electrical excitability of nerve tissues exposed tostatic magnetic fields have not demonstrated any robust
effect at field levels up to 2 T (Gaffey and Tenforde
1983; Hong et al. 1986).
A well-established effect of exposure of animals tostatic magnetic fields greater than about 0.1 T is theinduction of blood flow potentials in and around the heartand other major vessels of the central circulatory system(Gaffey and Tenforde 1981; Tenforde et al. 1983). These
are also well documented in humans (see below) but havenot been associated with any adverse effect in volunteer
studies. The presence of these induced voltages has been
demonstrated by electrocardiogram (ECG) studies inrodents, dogs, baboons, and monkeys performed duringexposures of several hours to several days duration
involving exposures up to 2 T (Tenforde 2005). However, their significance for health remains unclear. Extensive measurements in dogs and monkeys exposed to
1.5 T fields provided no evidence for changes in bloodflow rate, blood pressure, or cardiovascular dynamics(Tenforde et al. 1983). Exposures of several hours

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duration to an 8 T field had no effect on cardiovascularfunction in pigs (Kangarlu et al. 1999). Several otherstudies with rodents exposed to field levels ranging frommilliteslas to 10 T have led to reports of minor changes
in cardiovascular parameters such as blood pressure andflow rate (Ichioka et al. 2000; Okano et al. 2005; Okano
and Ohkubo 2006). However, the experimental endpoints
in these studies have generally been rather labile andsensitive to confounding factors such as anesthesia, andfirm conclusions cannot be drawn without independent
replication of the reported effects.
Exposure to static fields of up to 1 T has not been
demonstrated to have an effect on fetal growth or
postnatal development in mice (Sikov et al. 1979; Konermann and Monig 1986). Other studies report a lack ofeffect on mouse fetal development following brief (2–7d) exposure during organogenesis to fields of 4.7 T(Okazaki et al. 2001) and 6.3 T (Murakami et al. 1992).
There are few studies on possible genotoxic or
carcinogenic effects of static magnetic fields in laboratory animals (Bellossi 1984, 1986; Mevissen et al. 1993).
To date no lifetime exposure studies have been conducted to evaluate cancer induction or promotion bystatic magnetic fields. It is not possible to draw any
conclusions from animal studies regarding these particular endpoints and long-term health consequences ingeneral.
Several other endpoints that have been studied,including haematopoietic, endocrine system and blood
chemistry, have not provided convincing evidence of any
adverse effects (WHO 2006).
Laboratory studies in humans
Since the publication of the 1994 ICNIRP guidance(ICNIRP 1994), there have been a number of humanstudies evaluating the physiological and neurobehavioral
influence in humans exposed while stationary to static
magnetic fields of up to 8 T.
Detailed physiological studies evaluating various
physiological parameters including body (sublingual)temperature, respiratory rate, pulse rate, blood pressure,and finger oxygenation levels have not shown any
pronounced effects of exposure to magnetic fields up to
8 T (Chakeres et al. 2003a). Distortion of the electrocardiogram (ECG) signal was observed, which was causedby the induced flow potentials around the heart (seeabove). At 8 T, their magnitude was sufficient to render
the ECG uninterpretable; however, the heart rate was
unaffected. The only physiological parameter that demonstrated a statistically significant change was a small
increase of less than 4% in systolic blood pressure, whichlies within the range of a predicted increase in blood flow
resistance due to magneto-hydrodynamic effects. Based

April 2009, Volume 96, Number 4

on modeling of such effects, a clinically significant bloodflow reduction of ⬎10% is predicted only at field levels
in excess of 15 T (Kinouchi et al. 1996). The recorded
blood pressure change did not represent a clinicallysignificant or symptomatic alteration for healthy humansubjects and is well within normal physiological variation. There is no evidence in humans of effects of static
magnetic fields on other aspects of cardiovascular functions. It has also been reported that exposure of humanvolunteers to static magnetic fields up to 8 T does not
induce body temperature changes (Shellock and Crues
1987; Chakeres et al. 2003a). These findings have been
confirmed in a recent MRI study in which the static fieldcomponent was 9.4 T (Atkinson et al. 2007), but there wasno change in heart rate or systolic blood pressure. It should
be noted, however, that switched gradient and radiofrequency (RF) magnetic fields were also present in this study.
Recent neurobehavioral studies on humans exposed while stationary at field levels up to 8 T havedemonstrated no significant changes in many different
parameters, including short term memory, working
memory, speech, and auditory-motor reaction time
(Kangarlu et al. 1999; Chakeres et al. 2003b; Chakeres
and de Vocht 2005).
Behavioral studies carried out on subjects situated in
the proximity of MR systems of up to 7 T have suggested
that there may be a transient negative influence of
exposure on eye-hand coordination and visual contrast
sensitivity associated with head movement in the field(de Vocht et al. 2003, 2006a, 2007a, 2007b). De Vocht
and colleagues describe decrements in the performanceof a visual tracking and an eye-hand coordination task,
both specific measures of the vestibular-ocular reflex,
immediately following a standardized series of head
movements conducted in static fields of between 0.5 T
and 1.6 T, generating rates of change of field of up to 0.3
T s⫺1 (at 1.6 T). The magnitude of the effect seemed todepend on the time-varying flux of the field due to head
movement.
Several studies have reported that individuals exposed to static magnetic fields above 2–3 T experiencetransient sensory effects associated with motion in astatic field gradient such as vertigo, nausea, a metallic
taste, and magnetic phosphenes when moving the eyes orhead (Schenck et al. 1992; de Vocht et al. 2006a, 2006b;
Atkinson et al. 2007). However, the incidence andseverity of these symptoms can be decreased by slowing
the rate of motion of an individual through the magnetic
field gradient (Chakeres and de Vocht 2005).
The theoretical and experimental basis for magneticfield-induced vertigo experienced by people working inand around strong static magnetic fields has been investigated in some detail by Glover et al. (2007). Movement

ICNIRP guidelines on limits of exposure to static magnetic fields ● ICNIRP

of volunteers into the bore of a 7 T whole-body magnet
at a speed of 0.1 m s⫺1 resulted in a sensation of rotation(pitch forwards or backwards) in some but not all of thesubjects. This direction of apparent rotation was reversed
when the orientation of the subject was reversed inrelation to the field, e.g., by moving from a supine to aprone position, suggesting an effect of induced current on
the neural output of the vestibular system. Head movement within the homogeneous (zero gradient) field at thecenter of the magnet resulted in mild to severe vertigolike effects, with two subjects experiencing severe nausea. These feelings persisted for up to 30 min.
In contrast to movement-induced effects, postural
sway was significantly increased in some (less than 50%)of the subjects standing stationary adjacent to the MRI
scanner in a field of ⬃0.8 T. The effect is thought to beconsistent with differences in magnetic susceptibility
between the calcite crystals that comprise the otoconia(otoliths) of the vestibular organ and the surrounding
fluid (Glover et al. 2007).
It is clear that sensitivity to these effects varies considerably between individuals. Thresholds for motion-induced
vertigo in sensitive people were estimated to be of the orderof 1 T s⫺1 for greater than 1 s, and of a field-gradientproduct of 1 T2 m⫺1 for postural sway. The long integration
times required for these effects to become apparent are
indicative of the relatively low frequency response of thevestibular system (0.4 – 4 Hz).
A study of workers engaged in the manufacture of
1.0 T and 1.5 T MRI equipment (de Vocht et al. 2006b)
investigated the incidence of sensory symptoms, assessedby questionnaire at the end of each working shift, and theperformance of cognitive tasks, tested before and directly
after a working shift. The results indicated that, during
the work shift, the occasional reports of vertigo, ametallic taste in the mouth, and concentration problems
occurred more frequently in those involved in MRI
manufacture compared with controls. In general, these
symptoms occurred more often in workers who moved
quickly compared with those moving more slowly, although there was considerable inter-individual variability
in sensitivity. However, there were no significant decrements in cognitive performance following each work
shift compared with values assessed before work. The
results support the view that magnetic-field-induced
effects on cognitive performance reported in other studies are transient.
In conclusion, current information does not indicate
any serious health effects resulting from the acute exposure of stationary humans to static magnetic fields up to
8 T. It should be noted, however, that such exposures canlead to potentially unpleasant sensory effects such as509

vertigo and transient decrements in the performance ofsome behavioral tasks during head or body movement.
Epidemiological studies
The few available epidemiological studies havemostly been conducted on workers exposed to moderatestatic magnetic fields of up to several tens of mT either
working in aluminum smelters or chloralkali plants or as
welders. However, such work is also likely to involve
exposure to a variety of potentially hazardous substances,such as coal tar pitch and polycyclic aryl hydrocarbons,
which may confound the results. In addition, the static
fields used in industrial processes such as electrolysis areproduced by rectified power supplies with imperfectsmoothing, so extremely low frequency (ELF) fields arealso present. Assessment of static magnetic field exposure has been poor or nonexistent, and in some of thestudies the number of participants has been very small.
Health endpoints studied include cancer incidence, hematological changes and related outcomes, chromosome
aberrations, reproductive outcomes, and musculoskeletal
disorders.
Rockette and Arena (1983) studied a large cohort ofmale aluminum workers comparing the mortality among
aluminum workers with that of the general United States
male population. They reported a slightly higher than
expected mortality from pancreatic, genitourinary andlympho-hematopoietic cancers, although not statisticallysignificant. Static magnetic fields were not measured,and could not be separated from other exposures present
in the work environment. Spinelli et al. (1991) reported asignificantly increased risk of brain tumor mortality [standardized mortality ratio (SMR) was 2.2; 90% confidence
interval (CI): 1.2–3.7] and non-significantly increased leukemia mortality (but not incidence), which did not appear to
be explicable by coal tar pitch volatile (CTPV) exposure, ina cohort of aluminum workers. (There were also increases
in other cancers related to CTPV exposure.) The authors
found no increased risks associated with cumulative exposure to static magnetic fields. Two small Norwegian studiesof aluminum workers reported no increased cancer risk
associated with estimates of static magnetic field exposure(Rønneberg and Andersen 1995; Rønneberg et al. 1999). Ina study of French aluminum workers conducted by Mur etal. (1987), cancer mortality and mortality from all causes
were found not to differ significantly from the levels
observed for the general male population of France.
Studies of chloralkali workers in Sweden and Norway (Ellingsen et al. 1993) reported increased risks oflung cancer of borderline statistical significance, but did
not attempt to estimate magnetic field exposure. These
workers were also exposed to other agents such as
mercury vapour. No control of potential confounding

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from smoking was made. Bårregard et al. (1985) conducted a study on a cohort of workers at a chloroalkali
plant where the 100 kA direct currents used for theelectrolytic production of chlorine gave rise to static
magnetic flux densities at worker locations ranging from4 to 29 mT. The observed incidence of cancer among
these workers over a 25-y period was not significantly
different from that expected.
Non-cancer health effects have been consideredeven less frequently. Most of these studies were based onvery small numbers and had numerous methodologicallimitations. One of the larger studies examined fertility
and pregnancy outcome in 1,915 female MRI operators(Kanal et al. 1993), possibly involving exposures tofields up to ⬃1 T. The risk of miscarriage for pregnancies during MRI work was slightly increased (not statistically significant) compared with work in other jobs andconsiderably higher than the risk in housewives. Minor
differences were found for early delivery and low birthweight when compared with housewives, but not whencompared with other workers. Age was not controlled in
the analysis. The MRI workers were markedly older thanthe other groups, and selection bias may have affected
this cross-sectional study.
Overall, the few available epidemiological studies
have methodological limitations and leave a number ofissues unresolved concerning the possibility of risk ofcancer or other outcomes from long-term exposure to
static magnetic fields. These studies do not indicate
strong effects of static magnetic field exposure of thelevel of tens of mT on the various health outcomesstudied, but they would not be able to detect small tomoderate effects. Other occupations with a potential forhigher magnetic field exposures have not been adequately evaluated, e.g., MRI operators.
EXPOSURE LIMITS
Separate guidance is given for occupational exposures and exposure of the general public. It is recommended that the limits for occupational exposure in theseguidelines be applied to those individuals who areexposed to static magnetic fields as a result of performing
their regular or assigned job activities. The term “generalpublic” refers to the entire population.
Occupational exposures
Exposure limits. It is recommended that occupational exposure of the head and trunk should not exceed
a spatial peak magnetic flux density of 2 T except for thefollowing circumstance: for work applications for which
exposures above 2 T are deemed necessary, exposure up
to 8 T can be permitted if the environment is controlled

April 2009, Volume 96, Number 4

and appropriate work practices are implemented to control movement-induced effects. Sensory effects due tothe movement in the field can be avoided by complying
with basic restrictions set in the ELF guidelines. When
restricted to the limbs, maximum exposures of up to 8 T
are acceptable.
Explanation. Development of guidelines for static
fields raises two difficult issues. First is the extent, if any,
to which guidelines should allow potential occurrence, insome exposed workers, of temporary sensory effects withno known long term or serious consequences. Second is
the extent to which restrictions should prevent levels of
exposure higher than those for which there is humanexperience hence for which there is no known adverse
effect but a concern about lack of knowledge. With
regard to the first issue, ICNIRP considers that there areoccupational circumstances where, with appropriate advice and training, it is reasonable for workers voluntarily
and knowingly to experience possible transient sensory
effects such as nausea, since they are not believed to leadto long term or pathological health effects. With regard to
the second issue, ICNIRP considers that the exposurespermitted under the guidelines should be based on levels
for which there is appreciable evidence, and should not
go higher than this merely because of lack of evidence ofadverse effects.
Note: It is recognized that, for research purposes,
there might be a wish to investigate the effects of thesehigher levels; such experimental exposures, however, area matter for ethics committees (institutional review
boards).
Since publication of the 1994 guidelines there havebeen several studies on humans exposed to static magnetic fields up to 8 T (Kangarlu et al. 1999; Chakeres etal. 2003a, 2003b; Glover et al. 2007). Above 2 T,transient effects such as vertigo, nausea and phosphenes
have been occasionally observed in some people, but noevidence has been found for any irreversible or serious
adverse health effects. Because the vestibular system is
optimally stimulated by low frequency (around 1 Hz),
induced electric fields or currents (Stephen et al. 2005) atlevels below nerve stimulation thresholds (Glover et al.
2007), it is considered that protection against vertigo andnausea will provide adequate protection against othereffects of induced currents in the head and trunk such as
peripheral nerve stimulation.
In animal studies aversion responses, which may
have resulted from similar effects, have been observed
between 4 T and 14 T. However, there is no evidence up
to 8 T of clinically significant cardiovascular or neurological effects, which are the major potential concernswith respect to limiting exposure to static magnetic

ICNIRP guidelines on limits of exposure to static magnetic fields ● ICNIRP

fields. Therefore, for general workplaces, the limit on
exposure is set at 2 T, to prevent vertigo, nausea andother sensations, but for specific work applications, whenthe environment is controlled and appropriate work
practices are implemented, then exposure up to 8 T is
acceptable. The extent of these sensations is highly
dependent on individual factors such as personal propensity to motion sickness and the speed of movement in thefield; therefore, if an individual experiences such effects,
they can be avoided or minimized by moving as slowly
as possible. Guidance is not based on time-averaged
exposure because, in addition to the experience gainedwith the use of MR and other static field sources
world-wide over the last 20 y, mechanistic considerations
indicate that any effects are likely to be acute.
Adverse effects on the limbs from exposures up to 8
T are not expected based on modeling of blood flow insmaller vessels compared with those of the head andtrunk, and experience from existing sources. There is noevidence on which a higher limit of exposure for thelimbs can be based.
General public exposures
Exposure limits. Based on scientific knowledge on
the direct effects of static fields on humans, acuteexposure of the general public should not exceed 400 mT(any part of the body). However, because of potential
indirect adverse effects, ICNIRP recognizes that practicalpolicies need to be implemented to prevent inadvertent
harmful exposure of people with implanted electronic
medical devices and implants containing ferromagnetic
materials, and injuries due to flying ferromagnetic objects, and these considerations can lead to much lower
restriction levels, such as 0.5 mT (IEC 2002). The
exposure limits to be set with regard to these nonbiological effects are not, however, the duty of ICNIRP.
Explanation. These ICNIRP guidelines are basedon direct biological effects of static magnetic field
exposure. There are, however, other hazards of static
fields that are not directly biological and therefore not thepurview of ICNIRP, but are nevertheless important tohealth protection (see section on protective measures).
Based on the available scientific data above 2 T, theexposure limit for the general public (any part of thebody) is derived by applying a reduction factor of 5 withrespect to the occupational limit for the head and trunk.
This reduction factor accounts for all members of the
population.
The limits recommended for occupational and general public exposures to static magnetic fields are summarized in Table 2.

511

Table 2. Limits of exposurea to static magnetic fields.
Exposure characteristics

Magnetic flux densityb

Occupational
Exposure of head and of trunk
Exposure of limbsc
General publicd
Exposure of any part of the body

2T
8T
400 mTa

ICNIRP recommends that these limits should be viewed operationally as
spatial peak exposure limits.
For specific work applications, exposure up to 8 T can be justified, if theenvironment is controlled and appropriate work practices are implemented
to control movement-induced effects.
c
Not enough information is available on which to base exposure limits
beyond 8 T.
dBecause of potential indirect adverse effects, ICNIRP recognizes thatpractical policies need to be implemented to prevent inadvertent harmful
exposure of persons with implanted electronic medical devices andimplants containing ferromagnetic material, and dangers from flying
objects, which can lead to much lower restriction levels such as 0.5 mT.
b

PROTECTIVE MEASURESICNIRP recommends that the use of these guidelines should be accompanied by appropriate protective
measures. These measures need to be considered separately for public places where exposures to static magnetic fields are likely to be very low and infrequent, andworkplaces where, in some work situations, strong static
fields may be regularly encountered.
There are three main areas of concern: for membersof the public, there is a need to protect people withimplanted medical devices against possible interference
and against forces on implants containing ferromagnetic
material. In addition, in some specific situations, there isa risk from flying ferromagnetic objects such as tools.
Thirdly, in work situations involving exposure to very
high fields, there is a need for a set of site-specific work
procedures intended to minimize the impact of transient
symptoms such as vertigo and nausea.
Effects on implanted medical devices
Safety authorities need to ensure that there are
restrictions to protect individuals who are wearing implanted ferromagnetic or electronic medical devices sensitive to magnetic fields. There are many individuals
wearing such devices, in some cases without being awarethat they have them (e.g., surgical clips).
Electromagnetic interference from low-intensity
static magnetic fields has been observed to affect theoperation of pacemakers, particularly those with magnetic switches, and other types of medical electronic
devices, including cardiac defibrillators, hormone infusion pumps (e.g., for insulin), neuromuscular stimulation
devices (e.g., for the sphincter muscle of the bladder),neurostimulators, and electronically operated prosthetic
devices (e.g., for the limbs and inner ear). In general, the512

Health Physics

operation of these devices is not adversely affected bystatic magnetic fields below 0.5 mT.
In addition to potential problems arising from electromagnetic interference, many implanted medical devices contain ferromagnetic materials that make themsusceptible to forces and torques in static magnetic fields.
These mechanical effects can lead to the movement andpotential dislodging of implanted ferromagnetic devices,
especially those of large size such as hip prostheses.
Other ferromagnetic devices that might be affected include aneurysm clips, metal surgical clips and stents,
heart valve prostheses and annuloplasty rings, contraception implants, cases of implanted electronic devices, andmetallic dental implants, although most modern implants
are not ferromagnetic. The safety of exposing thesedevices to the fields used in MRI has been extensively
studied (New et al. 1983; Kanal et al. 1990; Shellock andCrues 2004). From studies performed to date, there is noevidence that static magnetic fields at or below the levelof 0.5 mT would exert sufficient forces or torques onthese devices to create a health hazard.
Accordingly, warning signs or lines are drawn
around locations with magnetic flux densities ⬎0.5 mT
to mark public exclusion zones, for instance around MRI
systems.
Movement of metallic objects
Protection needs to be given against danger fromflying metallic objects moved by magnetic field forces.
Such risks occur in fields of the order of several
milliteslas. The 400 mT limit recommended by ICNIRP
is based solely on grounds of direct biological effects ofthe field and is greatly above the level at which accidents
can occur from mechanical forces on metallic objects;
hence, the appropriate safety authorities need to guard
the public against such mechanical hazards.
A 0.5 mT limit for protection of medical devices is
consistent with protection against flying metal objects
that experience substantial mechanical forces in static
magnetic fields. The amount of force imparted on suchobjects depends on their size and content of ferromagnetic materials, but fields with flux densities in excess ofa few milliteslas can cause significant rapid movement ofmany tools and other common metal objects.
Transient symptoms
For certain occupations, e.g., surgeons operating
within an open MRI device, acute exposure symptoms
such as nausea could affect performance and hence thesafety of the patients on whom they are operating.
Similarly, these acute symptoms could affect theaccident-proneness of a worker. Each such workplaceshould have a set of work procedures and practices

April 2009, Volume 96, Number 4

specific to the work situations that will minimize any
adverse consequences of exposure.

Acknowledgments—During the preparation of this document, ICNIRP wascomposed of the following members: P. Vecchia, Chairman, Italy; M.
Hietanen, Vice-Chairperson, Finland; A. Ahlbom, Sweden; L.E. Anderson,
United States of America (until 2006); E. Breitbart, Germany; F.R. de
Gruijl, The Netherlands; J.C. Lin, United States of America; R. Matthes,Germany; A.P. Peralta, The Philippines; P. Söderberg, Sweden; B.E.
Stuck, United States of America; A.J. Swerdlow, United Kingdom; M.
Taki, Japan; R. Saunders, United Kingdom; B. Veyret, France.
The working group who prepared the first draft of this document wascomposed of the following members: A.J. Swerdlow, Chairman; D.W.
Chakeres, United States of America; M. Feychting, Sweden; J. Hennig,
Germany; T.S. Tenforde, United States of America; E. van Rongen, The
Netherlands.
ICNIRP gratefully acknowledges the useful comments received frommany scientists through its external review process.
The support received by ICNIRP from the International Radiation
Protection Association, the World Health Organization, the European
Commission, and the German Federal Environment Ministry is gratefully
acknowledged.

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