University of
Guelph - Safety Policy Manual
Policy
851.09.04
Page 5 of
6
effects that may
be possible in higher frequency fields. Safety measures involve
engineered
controls (e.g.
interlocking, switching, filtering, grounding), isolating or shielding
the
source, wearing
RF-protective clothing, and using administrative controls such as
warning
signs, zoning,
restricting access, and limiting exposure time. Ultrasound has
widespread
uses in industry
(20-50 kHz) and medicine (1-15 MHz), though personal non-medical
exposures are
usually accidental or incidental to purpose.
Potential
adverse consequences, if any, might arise from the thermal and
mechanical
bioeffects of
ultrasound. Exposures to ELF occur primarily due to the generation,
transmission and
uses of electrical energy. ELF electromagnetic fields are known to
cause
biological
(enzymatic) effects, but the implications for human health have yet to
be
elucidated.
Occupational exposures to static magnetic fields (e.g. related to uses
of
magnetic
resonance imaging or magnetic levitation) are associated with no
known
irreversible
health effects.
Biological
Effects and Protection Standards
The nature,
extent, and physiological importance of biological effects from NIR exposures
will depend on
many factors such as the energy of the incident radiation (which determines
the penetration depth), the
power density of the field or beam, source emission
characteristics,
duration of exposure, environmental conditions, and the spacial
orientation
and biological
characteristics of the irradiated tissues (molecular composition, blood
flow,
pigmentation,
functional importance, etc.). In the lower frequency range (300 Hz to
1
MHz), induction
currents may interfere with the functioning of the central nervous
system.
In the
intermediate frequency range (100 kHz to 10 GHz), the absorption of
electromagnetic
energy generates heat. At the upper frequency range of 10 GHz to
300
GHz, heating of
superficial tissues is possible. It is generally recognized that, except
for
optical radiation, there is scant data on the quantitative
relationships between exposures to
different types
of NIR and pathological responses in humans.
The health
protection standards for NIR from different
authorities apply in general to
characteristic
parameters of the radiation field at the point
in space where the individual can
be or is
exposed. They are based on biophysical models and on laboratory and
field
observations of
the biological effects of electric and magnetic fields. The standards
are
limits
for field parameters (e.g. to limit current density, SAR, and power density)
which
are designed to
protect workers from potentially adverse effects of electromagnetic radiation
and to permit
the general use of NIR under safe conditions,
though there is no precise
boundary between
risk and no risk Equipment standards for the design, construction
and
performance of
NIR devices used for industrial, scientific,
medical, and home applications
also protect
workers and the public from unacceptable exposures. Occupational
exposure
situations must
be evaluated individually for risks and benefits. Normally, only a very
small
number of people
would ever be occupationally exposed to levels comparable to the
exposure
limits.