1
Threshold Limit Values
Static Magnetic Fields
The American Conference of Governmental
Industrial Hygienists (ACGIH) has developed
threshold limit values (TLVs) guidelines for static magnetic field flux densities to which it is
believed that nearly all workers may be exposed to day after day repeatedly without
experiencing adverse health effects.
The TLVs for a routine (8-hour) occupational exposure from static magnetic fields are listed in
Table 1. Workers with implanted ferromagnetic or electronic medical devices should not be
exposed to static magnetic fields exceeding 0.5 millitesla (mT).
Table 1.TLVs for Static Magnetic Fields
Exposure
8-hour TWA
(Time-Weighted Average)
Ceiling
Whole body
60 mT
600 G
2 T
20,000 G
Limbs
600 mT 6,000 G
5 T
50,000 G
Medical electronic
device wearers
0.5 mT 5 G
G = gauss; T = tesla
Sub-radiofrequency (30 kHz and Below) Magnetic Fields
These TLVs refer to the amplitude of the magnetic flux density (B) of sub-radiofrequency
(sub-RF) magnetic fields in the frequency range of 30 kilohertz (kHz) and below that nearly all
workers may be exposed to repeatedly without adverse health effects. The magnetic field
strengths in these TLVs are root-mean-square values.
Occupational exposures in the extremely low frequency range of 1–300 hertz (Hz) should not
exceed the values listed in Table 2.
Table 2. TLVs for Sub-RF (30 kHz and Below) Magnetic Fields
Exposure
Frequency Range
TLV/Ceiling
Extremely low frequency
1 Hz to 300 Hz
B
TLV
(mT) = 60/f
60 Hz
1 mT
10 G
30 Hz to 30 kHz
0.2 mT
2 G
30 kHz at 160 A/m
0.2 mT
2 G
Whole and partial body
300 Hz to 30 kHz
0.2 mT
2 G
Hands and feet
<300 Hz
2 mT
20 G
Arms and legs
<300 Hz
1 mT
10 G
Point contact current
1 Hz to 2.5 kHz
1.0 mA
2.5 kHz to 30 kHz
0.4·f mA (f in kHz)
A/m = amperes per meter; B
TLV
= magnetic
flux density, measured in millitesla (mT); f = frequency, measured in
Hz; mA = milliampere
2
Sub-radiofrequency (30 kHz and Below) and Static Electric Fields
The TLVs listed in Table 3 refer to the maximum unprotected workplace field strength of sub-RF
electric fields (30 kHz and below) and static electric fields. They represent conditions on
limiting
the currents on the body surface and induced internal currents to levels below those that all
workers may be exposed to repeatedly without adverse health effects. The electric field
intensities in these TLVs are root-mean-square values. The electric field strengths stated in
these TLVs refer to the field levels present in air, away from the surfaces of conductors (where
spark discharges and contact currents may pose significant hazards).
Table 3. TLVs for Sub-RF (30 kHz and below) and Static Electric Fields
Exposure
Frequency Range
TLV/Ceiling
Whole body and partial body
0 Hz (DC) to 100 Hz
25 kV/m
100 Hz to 4 kHz
E
TLV
= 2.5 × 10
6
/f
4 kHz to 30 kHz
625 V/m
E
TLV
= electric field strength in volts per meter (V/m); kV/m = kilovolts per meter
Field strength greater than approximately 5–7 kV/m can produce a wide range of
safety
hazards, including startle reactions associated with spark discharges and contact currents from
ungrounded conductors within the field. In addition, safety hazard associated with combustion,
ignition of flammable materials, and electro-explosive devices may exist when a
high-intensity
electric field is present. Care should be taken either to remove ungrounded objects or to
ground them; in addition, ensure that insulated gloves are worn when handling ungrounded
objects. Use protective devices (e.g., suits, gloves, and insulation) in all fields exceeding 15
kV/m.
For workers with cardiac pacemakers, the TLVs may not protect against electromagnetic
interference with pacemaker function. Some models of cardiac pacemakers have been shown
to be susceptible to interference by power-frequency (50 to 60 Hz) electric fields as low as 2
kV/m. It is recommended that the exposure of pacemaker and medical
electronic device
wearers be maintained at or below 1 kV/m.