006898
WORK STAUONMA&miC FIELD SURVEY RESULTS
IN WE MEKALFE FEDERAL BUILDING
-------
INDEX
A. Background
B. Survey Methodology
C. Averages for Specific Areas
D. Region I Survey Results
E. Summary
F. Appendices
-------
A.. BACKGROUND
On November 23, 1993, the Radiation Section (renamed the Radiation and Indoor
Air Section) submitted a proposal to survey oscillating magnetic field
intensities on USEPA-occupied floors in the Metcalfe Federal Building. The
proposal was submitted at the request of the Regional Health and Safety
Committee. The Regional Health and Safety Committee requested that the Air
Toxics and Radiation Branch, Radiation Section, conduct a survey of the
electric and magnetic field levels to which workers in the Metcalfe Building
are exposed.
Magnetic field strength is measured in gauss or milligauss. A milligauss (mG)
is I/1000th of a gauss. Background magnetic field measurements taken outside
of the Metcalfe Building range from 0.7 mG to 1.0 mG. Away from all
appliances, a typical American home has background magnetic field levels
ranging from 0.5 mG to 4 mG. The actual strength of the field at any given
place in a room depends upon the number and kinds of sources, how far away
they are, and how many are operating at one time.
No clear cause-and-effect relationship exists between magnetic fields and
adverse health effects. Consequently, no national standards exist for
exposure to magnetic fields in the United States. Also, it is not understood
whether proximity to or duration within a magnetic field may contribute to
adverse health effects.
Despite the lack of evidence regarding the relationship between magnetic
fields and disease, organizations such as the World Health Organization,
International Non-Ionizing Radiation Committee (WHO/INIRC) has proposed a
5,000 mG magnetic field intensity exposure limit. The American Conference of
Governmental Industrial Hygienists (ACGIH) has recommended a 600,000 mG
occupational limit.
Jack Barnette, Radiation and Indoor Air Section Chief, believes that the
exposure limits set by WHO/INIRC and ACGIH are problematic. "In light of what
we now know about biological effects from exposure to EMF and the public's
perception of potential risks, it would be imprudent to expose people to such
intense magnetic fields."
B.. SURVEY METHODOLOGY
In February, 1994, magnetic field measurements began to be taken on floors
occupied solely by USEPA employees in the Metcalfe Building. Following
protocols used by USEPA Headquarters, Region 1, the National Air and Radiation
Environmental Laboratory (NAREL), and the State of California, and employing
recently calibrated instruments from NAREL, the Radiation Section began a
stratified random sample. Both 5 percent of non-enclosed work stations and
5 percent of enclosed work stations were tested. Furthermore, copy rooms,
kitchenettes, and unique areas such as the main computer room and the library
were measured. Sampling ended in March, 1994, and the data was compiled.
-------
c.
AVERAGES FOR SPECIFIC AREAS
The following table provides a summary of the magnetic field survey. A room
description and the average of all the measurements for that room are given.
All average measurements have been rounded to the nearest hundredth of a
milligauss.
Room Description
Conference Rooms
Supervisor Offices
Offices (enclosed)
Work stations
File/Docket Rooms
Copy Rooms
Kitchenettes
Average Measurement (in mG)
0.36
2.30
1.67
1.37
0.66
4.38
2.62*
This figure does not include the 73.14 mG measurement
Of all the rooms sampled, the highest magnetic field measurements were found
in kitchenettes. This is not surprising, given the large number of appliances
that operate in these areas. The highest individual room measurement, 73.14
mG, was taken in the kitchenette on the eighth floor. Because measurement
protocols were not followed when this measurement was taken, a comparatively
higher measurement was recorded. To have a more accurate magnetic field
profile of this room, remeasurement following the appropriate protocols should
be performed.
Individual room measurements are provided in Appendix 1. Measurements taken
in unique areas, such as the library and computer room, are also provided in
Appendix 1.
JL.
REGION 1 SURVEY RESULTS
Magnetic field measurements taken in the Metcalfe Building may be meaningfully
contrasted with magnetic field research performed by other Regional offices.
In March, 1993, Region 1 published "Extremely Low Frequency [ELF] Magnetic
Fields in Offices', and Their Mitigation," in which 5 mG is cited as a "useful
tentative yardstick" for setting an occupational exposure standard in an
office (see Appendix 2). An overall range of 0.1 to 50 mG for occupational
exposure in a large office facility is cited as acceptable. All average room
measurements fall well within an acceptable overall range of 0.1 mG to 50 mG.
Region 1 also performed a magnetic field survey of USEPA facilities at Canal
Street and One Congress Street in February, 1993 (see Appendix 3). All the
offices tested in that survey registered values which fell in the range of 5
mG to 50 mG. Most of the work stations (95%) in both facilities registered
-------
values which fell within the range of 5 mG to 50 mG. As stated earlier, the
average magnetic field intensity for work stations in the Metcalfe Building
measured 1.37 mG, while Supervisor offices measured 2.30 mG, and other
enclosed offices measured 1.67 mG. These figures, when compared to those in
Region 1, indicate generally weak magnetic field strengths in the Metcalfe
Building. ^
E.. SUMMARY
This magnetic field survey provides an excellent profile of the magnetic field
environment in the USEPA-occupied portions of the Metcalfe Building. The
research protocols followed and the use of recently-calibrated NAREL
instruments ensure that the magnetic field profile presented here is accurate.
Based on this profile, magnetic field strengths in the USEPA-occupied portions
of the Metcalfe building appear to be on the lower end of the scale for a
typical office building.
Currently, research is unclear regarding the possible health effects of
exposure to magnetic fields in our everyday environment. USEPA has set no
standards for exposure to magnetic fields.
-------
APPENDIX 1
BYFLOOR
-------
Off1 BACXCaROQH) ABBtBBHBtT SURVEY
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EMF BACKGROUND ASSESSMENT SURVEY
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-------
APPENDIX 2
MAGNETIC FIELDS IN OFFICES,
AND THEIR MnKAJION"
-------
•HOTT.
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
3EGICN :
l.F. KENNEDY FEDERAL BUILDING. BOSTON. MASSACHUSETTS 02203-221 i
Extremely Low Frequency [ELF]
Magnetic Fields in Offices, and Their Mitigation
N. A. Beddows CM. CSP
Abstract
60 Hz, magnetic fields exist in the
occupiabie space of offices, generally at one-naif to
five milliCauss levels. In a relatively small number of
cases, magnetic flux density is higher, by two or
three orders of magnitude. This is attributable
invariably to closeness to fixed electrical equipment.
but only, within the facility. Elevated magnetic fields
are often discovered by a malfunction of a PC
monitor which is correctable by relocation.
Personal exposures and area flux density
can be measured. Two standards-setting
organizations have established daily occupational
limits for exposure. The World Health Organization
(WHO) daily, occupational limitation is 0.5 milHTesta
(5.000 milHGausst. This is based on potential
induction of a current density level (~ 10 mA. m*)
which is comparable to the levels occurring normally
in the body. The WHO limitation is lit three orders of
magnitude greater than the magnetic flux density
which exists in most occupiabie spaces. (HI seldom
if ever encountered in offices, and (Hit is far greater
than the minimal level which affects computer
monitors (10 milHGausst.
A tentative 'yardstick' for magnetic flux
density in offices is five milliCauss. No deterioration
of acceptable work space quality, and minimizing
potential exposures is appropriate and prudent
policy. „ . •
Bevtttd field strengths in offices may be
reducible, economically, by a judicious use of low
carbon steef end/or 48% or 80% nickel content
alloys. A magnetic shield must have very low
reluctance and remain unsaturated. When wall
shielding is required. 80% nickel content alloy is
especially useful because of its high permeability.
Shield design involves attaining low
magnetic reluctance while averting magnetic
saturation, and excessive incremental structural
loading, thermal overloading, disruption to business,
and costs.
Success in shield engineering is meeting the
customer's expectation. In many mitigation projects.
this translates to a twenty to thirty decibel average
attenuation in flux density in occupiabie spaces.
Feasibility of successfully, economically
engineering a solution to an intrusive magnetic field
problem can be evaluated. Mitigation projects are
described. To assure project reliability and cost-
containment, the services of a shielding specialist
who can demonstrate capability and experience is
desirable, and may be necessary.
.•• This material summarizes certain personal recent
inquiries and findings on the practical aspects of
magnetic fields in offices, consequences of their
presence, and mitigation possibilities. It is intended
to be useful in a practical sense to office and
facilities managers, and employees who are looking
for basic information on the captioned subject, and
as relevant safety engineering material.
•" Disclaimer: The information presented is
believed, out is not claimed, to be accurate. No claim
is made or implied for any agency, official or
committeeandorseaent, concurrence, perspective or
approval. No endorsement or warrantee of any
product, process or service is made or implied. This
material is the sole work product and responsibility
of the author.
N.A.8. 3/25/93
HUNTED ON MCYCJ.EO
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Introduction
Magnetic fields are non-ionizing.
Unlike X-rays and other types of ionizing
radiation, including sunlight, they do not
cause actual breakage of molecule bonds.
However, they can induce low density
electrical currents into the head and trunk.
Magnetic fields are not perceived by
humans, and they can penetrate non-
ferromagnetic materials, unlike electric
fields which cause hairs on the body to stand
up, and which are stopped by all materials.'0
Extremely low frequency (ELF)
magnetic fields occur in every office
environment. Their frequencies are predomi-
nantly 60 Hz, with higher harmonics to 300
Hz. Other, lower frequencies (e.g., 5 Hz)
occur. These fields are created by alternat-
ing current in single-phase or three-phase
electrical conductors.m The 60 Hz flux
density average levels in the occupiable
spaces of most offices are about one-half to
five milliGausst, but the average magnetic
flux density levels may be elevated in a
relatively small number of cases. And, of
course, some variation can exist within each
setting. The existence of ELF magnetic
fields in offices is now well-known. First
evidence of their presence is likely to be
computer screen flickering which stops when
the monitor is placed outside of the fields.
An ambient magnetic flux density of about
ten milliGauss will cause a monitor to jitter
or lose image, or color integrity. PC
computers themselves create external
magnetic fields. Their contribution to the
average flux density in an office is minor.
t MilliGauss is used in field surveying; and
microTesIa, in Industrial hygiene and health
physics, for exposure. Some interchanging of
flux density terms is necessary in this paper to
maintain the broad perspective.
Personal exposures from PC
computers, even ones with high resolution
monitors, are rrujiimal, about one-tenth to
one-half of a microTesIa, at about (i) 24
inches from the screen and (ii) 36 inches
from the side or back of any nearby unit.
Average magnetic flux density levels
several orders of magnitude greater than the
upper limit of the general office range may
be encountered in a relatively small number
of offices. Elevated average flux density is
attributable invariably to proximity to
unshielded bus bars, distribution centers,
open cabling in trays, or cabling in walls.
Exposure to magnetic fields in
offices may become a concern in some
situations. The public is aware that
associations between various cancers and
leukemia and electromagnetic fields have
been claimed in some epidemiologic
studies.m And, public exposures and
possible biological effects have been
featured recently in the press and televisionr
Explaining, magnetic fields and discussing
the associations of potential exposures and
diseases is difficult. The popular media have
heightened public awareness of issues sur-
rounding magnetic field exposures, however,
some underlying factual aspects have gone
unrealized. Some studies which suggest a
cancer association with electromagnetic
exposures were based on indirect
assessments of exposure, such as the wiring
codes employed in home construction in
geographic areas near power lines, rather
than actual measurement of magnetic flux
density. Some studies which suggest
associations between health and magnetic
fields indite exposures which are less than
the theoretical threshold level for creation of
an electrical current density in the head or
trunk which is comparable in magnitude to
current density levels which occur in normal
body processes. And, some studies indicate
-------
that there is no significant linkage at che
surrogate exposure levels reported in studies
whach suggest some association. Other
studies indicate that weaker magnetic field
flux densities are associated with an adverse
response, while stronger ones are not;<4) and,
data in some studies would even support a
hypothesis of potential, beneficial effect. At
this time, it is evident that there is extreme
uncertainty in effect-exposure-response mat-
ters concerning weak magnetic fluxes.
In considering the epidemiological
reports on extremely low frequency
magnetic fields, it may be helpful to know
the position'51 of the World Health
Organization, International Non-Ionizing
Radiation Committee (WHO/INIRC) of the
International Radiation Protection
Association, The WHO/INIRC states:
" Although these epidemiological data
can not be dismissed, there must be additional
studies before they can serve as a basis for
health hazard assessment. Furthermore, scant
laboratory evidence exists to support the
hypothesis that there is an association between
50/60 Hz fields and increased cancer risk.'
The preceding WHO/INIRC position
is echoed by other authorities, including the
National Radiological Protection Board
(NRPB), and the Committee on Interagency
Radiation Research and Policy Coordination
(OSTP). These organizations and others,
however, support a major research initiative.
And, on this point, to quote the EPA
Scientific Advisory Board:
'Restjtrch is needed. The
Subcommittee therefore recommends that
scientific information sufficient to support
credible formal risk assessment of exposure to
electric and magnetic fields be developed..... *
EPA is pursuing research on ELF
and higher frequency band, electromagnetic
fields; with cancer, bio-mechanisms and
exposure assessment being high priorities.
Flux Density Levels & Factors
Strong magnetic fields do not exist in
occupiable spaces in a typical large office
facility. The average, 60 Hz magnetic field
flux density in such spaces in most offices in
a typical large facility, is less than five
milliGauss, and the corresponding range is
typically about an order of magnitude.
However, a small percentage of offices ui
such a facility may have (i) higher than
average flux densities and (ii) area magnetic
hot-spots due to the influence of external but
close, fixed power distribution centers, bus
bars, open cabling in trays, sub-stations,
elevator machinery rooms, electrical cables
in walls or main-frame computer equipment.
The materials used in construction, and
room orientation also can influence the level
of effect from electrical apparatus.
Magnetic field flux density at a point
is weakened greatly by separation of the
point from the source. Attenuation is an"
inverse function of the square of the
distance.(4) In most office layouts, separation
of occupied space from fixed high-power
electrical services or equipment is
substantial. Some offices will be close to,
and affected by, such electrical services or
equipment.
With some affected offices,
rearrangement of desks, computers or seats
will reduce potential exposures or eliminate
video monitor problems. Some affected
offices, however, will need to be physically
shielded to adequately attenuate magnetic
fields created by external electrical apparatus
and cabling, if they can not be relocated.
Survey Meters &r Monitoring
Most office facilities have electrical
apparatus which generate two or three 60 Hz
harmonics, as well as lower frequencies.
-------
Monitoring^ magnetic flux density levels in
offices is performed using a survey meter
which can measure down to about one-tenth
of a milliGauss [0.01 microTesla] on the
maximum-sensitivity scale. The meter
should have an accuracy of ±5% at the
calibration frequency. It needs to be
accurate over the frequency range
encountered. Readout is "milliGauss" or
"microTesia." Apart from area survey
meters (which can also be used to determine
time weighted average exposures), magnetic
field dosimeters are available for monitoring
personal exposures. They can be linked to
data loggers to facilitate large scale data
collection and analysis.
A magnetic flux density meter uses
either a single-axis probe or a three-axis
probe. The single axis probe is sensitive to
a field only in one direction. This feature,
however, is invaluable in determining field
magnitude and direction, which is needed in
shield design work. When a single-axis
meter is used as an area or personal
dosimeter, the operator turns the probe in all
directions, takes spot measurements in three
perpendicular axes, computes the square
root of the sum of the squares of the three
perpendicular plane readings, and reports
the computed (rms) mean as the flux
density. Taking readings in the three axes is
necessary because of the vector nature of
magnetic fields. The computation is
conservative when the field is elliptically
polarized (as with a three-phase generator).
The three-axis probe simultaneously senses
magnetic fields in three perpendicular
directions. The meter automatically
integrates the three, directional flux densities
and displays a single (rms) value.
Survey meters and dosimeters must
be calibrated before use, and at least
quarterly. The calibration source must be
traceable to a national primary standard.
Guidelines for calibration are provided in
MEL-STD 4566A, and in an ANSI/IEEE'"
standard. Portable calibrators are available.
Users must follow the recommendations of
both the calibrator manufacturer and the
meter manufacturer.
A large number of measurements
need to be made over the day, when work
places or personal exposures are to be
characterized. This is necessary to factor in
power usage, which may or may not change
over time and cause a change in the ambient
magnetic field strength. Evaluating a work
space requires measuring the mean (three-
axes) flux density in at least five locations,
including the room center, any walls near
seating, and the wall centers and top and
bottom comers. Evaluating a personal
exposure involves determining the time
weighted average, mean flux density at waist
height.
When spot measurements are made
in occupied spaces for any purpose, upon art
employee's, request, it would be reasonable
to (i) explain what is being measured, and
(ii) make the results available. Transmittal
of data might best be made by letter, with a
clear explanation of the situation. This will
avoid misunderstanding or misinterpretation.
Guidelines & Limitations
A knowledge of guidelines and
limitations for occupational exposure and the
rationale for setting the limitations is
invaluable when potential occupational
exposure to magnetic Melds becomes an
issue. Two organizations provide relevant
occupational guidelines and limitations:
* The World Health Organization,
International Radiation Protection
Association, International Non-Ionizing
Radiation Committee (WHO/INIRC).
-------
> The American Conference of Govern-
mental Industrial Hygiemsts.'9' ACGEH.
The 1989 WHO/INIRC occupational
Limitation is die more stringent of the two
limitations.
The basic criterion of the WHO
limitation is a biological one. This criterion
is that of maintaining flux density below the
level which can induce an electrical current
density in the body of about 10 mA m'2.
The criterion limitation carries no
implication whatsoever that the referenced
biological change progresses to any adverse
health effect.
The WHO, International Non-
Ionizing Radiation Committee, in referring
to the daily magnetic field occupational
limitation, -states:
"The magnetic flux density, B, ... is
accepted as the most relevant quantity for
expressing magnetic fields associated with
biological effects."
to be conservative, current
densities induced by external... magnetic fields
should not significantly exceed 10 mA m*."
"[The limits recommended] correspond
to induced current densities that are at or
slightly above those normally occurring in the
body (up to JO mA m'). "
"[A reduction factor of ten is applied to
the WHO/INIRC occupational, whota-body
exposure limitation IS milliTesia) which
corresponds to an induced current density of
JO mA m'l because of the sparseness of data
on long-term exposures ...."
"[The xtO factor-modified] magnetic
flux density for continuous exposure in the
occupational environment is limited toO.SmT.'
The ACGIH Committee, in referring
to its occupadonal standards, states in the
preamble to all of the standards:
"[A limitation to which] it is believed
that nearly all workers may be repeatedly
exposed day after day without adverse health
effects.'
The 1993 ACGIH occupational limit
is 60 milliTesia, it is unchanged from 1992.
OSHA':m has no applicable standard,
and its [§5(a)l] General Duty clause is not
applicable because no recognizable, serious
hazard exists. Electromagneuc exposure is
not on the 1993 OSHA Regulatory Agenda.
A Yardstick for Decision-Making.
Minimizing Potential Exposures
Offices in proximity to large, fixed
electrical equipment can be expected to have
stronger field strengths than offices which
are remote from such equipment. If higher
than average magnetic fields being present
in an office becomes an issue, some sort of
yardstick will be needed for making a
decision. If one accepts the WHO/INIRC
daily occupational limitation as a
conservative guideline (many industrial
hygienists do), and, that the magnetic field
flux density in a typical large office facility
is two or three milliGauss, which is three
orders of magnitude lower than the
WHO/INIRC limitation, then one might
agree that a useful tentative yardstick for
decision-making is five milliGauss, or one-
half of a microTesla, in exposure terms. [At
this flux density, one would not expect any
interference with computer monitors].
Apart from having an acceptable
yardstick for use in decision-making, one
might also want to employ certain criteria
for prudent avoidance, even though no basis
exists to believe that there is any degree of
hazard with office-level exposure. One may
elect to adopt measures to avoid exposures,
even if doing so may or may not reduce any
potential, albeit unknown, risk. A criterion
for this philosophy could be one of "no
significant deterioration." Another criterion
could be a goal of reducing flux density
when this is practicable and economical.
-------
The relation of the WHO/INIRC and
ACGEH guideline-limitations and typical
levels of magnetic flux density in offices is
illustrated in the following text box.
1992 - 1993 ACGIH
OCCUPATIONAL LIMIT •
60 MidiTesla.
DAILY.
££ 2 ORDERS OF MAGNITUDE
LOWER *
r
1989 [&. 1993] WHO / INIRC
DAILY, OCCUPATIONAL LIMIT -
0.5 MilliTesla. [5.000 MilliGaussl
3 ORDERS OF MAGNITUDE
LOWER, AGAIN *
PC Video Problems
[at 10-t- MilliGauss]
MOST OFFICES at 5 MilliGatm or
Less. [0.5 MicroTesJa or Less!
Reducing office magnetic field
strengths might require physically shielding
a work space from intrusive magnetic Melds
emanating from adjacent electrical power
apparatus, equipment or cables. Reducing.
personal exposures might be achieved by
rearranging, desks'and seats, or relocating an
employee. [Relocation might be offered as
an accommodation for an employee].
Regardless of whether an engineering or an
administrative effort is made, an assessment
of the area "will be needed. This will involve
representative monitoring of office spaces.
Characterizing an office facility and
assessing potential exposures in offices
require a large data base of magnetic flux
density and duration of exposure. Data
ought to be resolved in terms of office-flux
density distributions. Setting an overall
range for this purpose is arbitrary, but it can
be done sensibly. A range of 0.1 to 50
milliGauss is believed to be appropriate,
because: (i) the upper limit is rwo orders of
magnitude below the WHO limitation, and is
only rarely exceeded in offices; and (ii) 0.1
milliGauss is the lowest flux density which
one can measure ordinarily.
Depending on observations, the
quality of the available information, and the
reference point (yardstick) used, one can
decide whether or not to mitigate a flux
density problem in a particular work space.
In this matter, one might bear in mind that:
• Optimal work space quality may be
equated to magnetic field flux density, but it
is most definitely related to good lighting,
uniform acceptable temperatures, low noise^
level, and a high rate of fresh air supply;
compromise is needed, invariably.
« Employees having to work with
continually malfunctioning video monitors is
unacceptable, might be construed to be an
ergonomic hazard, and ought not to be pan
of a space-quality compromise.
• Work places which are perceived to
be of less-than-optimal quality might better
be used for minimal-occupancy activities:
record-keeping, and equipment storage.
• There is no requirement on an
employer to make an extraordinary effort to
measure or attenuate magnetic fields in
offices when there is no likelihood of a
recognizable serious health hazard existing.
Initiating such an effort, however, may be
necessary to maintain good employee
relations and productivity.
-------
Economically Feasible Engineering.
When considering the desirability of
reducing potential personal exposure or
eliminating electronic interference,
associated with an intrusive magnetic field
caused by an external electrical current, the
manager needs answers to two questions:
o What is involved in, and what is the
economic feasibility of, attenuating magnetic
fluxes in an affected work space?
o What has been successful in efforts to
attenuate intrusive magnetic fields using
economically feasible and practical methods?
Project performance data is propriety
information to the designers and installers of
magnetic shields. One respected source for
shield design and manufacture conditionally
agreed to provide the writer with pre-
treatment and post-treatment, average flux
density data and information on
methodology and material selection, for
several remedial projects. These particular
projects were described as 'conventional and
generally economical." The prescribed
conditions were: (i) data were to be
described in terms of "attained minimal
decibel attenuation" [rather like acoustical
engineering] and, (ii) only a general
description would be made of the
construction materials and arrangements
used. These restrictions, however, do not
prevent one from assessing the feasibility of
employing economical engineering to
attenuate fields to eliminate an equipment
interference problem or an exposure issue.
And, they do not stop one from providing a
sense of the engineering effort that can be
involved in their mitigation. Feasibility
information, and summaries of reported
projects are provided in the following parts.
1. Feasibility-Related Information,
• Intrusive magnetic fields can be
attenuated to non-problematic average flux
density levels by implementing a program of
surveillance, shield design and installation.
• Success, in context with economical,
conventional shielding for offices and
laboratories, means attaining the goal set by
the customer. Depending on the average
value of flux density initially existing, an
attenuation of average flux density of twenty
to thirty decibels or greater may be attained
without having to resort to extraordinary
(high cost) shielding engineering. In general,
the lower the value of the starting point flux
density, the lower will be the decibel level
of attained attenuation.
• Conventional magnetic shielding
design and installation has had many
customers with office type problems. The-
record of numerous projects is evidence for
the economic feasibility of shielding offices.
• Methodology for assessing
economical engineering feasibility is
illustrated in the following example:
A large, premium office space is being
affected by intrusive magnetic fields believed to
be caused by apparatus in an accessible
electrical, vault situated in a basement
immediately below the affected space. One
employee, using an inexpensive hobby-type
Gaussmeter, has found about 50 to 60
milliCauss in the occupiable spaces, and higher
levels on some walls. The management wants
to make the occupiable space the same,
magnetically, as the other (unaffected) offices,
but, it 7i 'nor~ going to pay for any
extraordinary engineering work. * The Building
Manager has asked 'Would using physical
shielding be feasible? What would be
involved?'
-------
The level to be attained is the "good"
office average level, say, an average of two
milliGauss. Let us accept that the meter which
the employee used was fairly accurate. The
preliminary challenge is to assess the feasibility
of attenuating flux density from an average of
sixty (Hmj to an average of two (H,) milliGauss,
using conventional, economical shielding
engineering (which may yield 20 decibels
-------
-- 9
• Efficient shielding is a matter of ' 2. Reported Successful Projects.
balancing permeability against saturation, !
while maintaining material workability, and
project simplicity and economy.
• Multiple layers of material or a
laminated arrangement may have to be used
in some cases for efficiency. Laminar
structures offer the great benefit of effective
attenuation by air spacing.
• It is generally preferable to shield the
source, when possible, consistent with
maintaining adequate heat dissipation and
required equipment operational
temperatures. The benefits are (i) generally,
minimal surface area treated, and (ii)
minimal disruption of work place activities.
• Shielding at the receptor site may
involve affixing one-quarter or even one-half
inch thick, low carbon steel plates to floors,
and a laminate of low carbon steel,
plywood, and a 80% nickel content alloy to
walls. Placing a one-quarter inch thick steel
plate on a floor creates an incremental
uniform loading of about ten pounds per
square foot. Generally, this level of
incremental floor loading is not a problem.
Shielding arrangements of these types,
reportedly, are quite usual as required
treatment for affected work spaces.
In some circumstances, an alternative
(or a compttmtnttfy action) to physical
shielding might b* a preferred solution. Such an
alternative might include • but is limited to •
eliminating open bus ban and replacing them
with shielded cables, twisting three-phase
conductors ~to achieve EMF-cancellation, re-
routing cabling to achieve maximum distance
from the affected receptor site, and terminating
conduits in heavy steel enclosures to further
confine magnetic fields.
Reportedly successful cases, for
which certain proprietary information and
attenuation data have been provided, are
described in the following sections.
• A large room with interference of
computer operations and video screen
problems, caused by external magnetic
fields, was treated successfully by covering
certain wall sections, which had magnetic
hot-spots, with 60 mil thick, 80% nickel
content alloy sheeting; and the floor, with
one-quarter inch thick, low carbon steel
plates. Reported average attenuation: 30 dB.
• A room with sensitive electronic
analytical equipment was affected by
magnetic fields created by a power control
center in a vault below the room.
Elimination of interference, with an average
ambient flux density less than ten milli-..
Gauss, was attained. Reportedly, this
involved using 1/4" 1010 steel plates for the
floor, and 60 mil, 80% nickel content alloy
sheets for the wall, magnetic hot spots.
Average flux density attenuation: 30 dB.
• A hospital room affected by 60 Hz
magnetic Melds from adjacent power
distribution equipment, reportedly, was
effectively treated using only low carbon
steel plates placed on the floor and on some
wall areas. Average attenuation: 25 dB.
• Designed, fabricated-to-order, nickel
alloy (high magnetic permeability)
enclosures are reported to be effective in
shielding video monitors from screen jitter
and image distortion caused by ambient 60
Hz magnetic Melds created externally.
Reported average attenuation: 40+ dB.
-------
10
Concluding Remarks
It may be worth summarizing a
personally associated, failed project: Low
carbon steel plates were fixed to the ceiling
of a power distribution equipment vault
located almost directly beneath offices which
were having problems with video monitors.
The average flux density in the vault space
exceeded 40 Gauss. The average flux
density in the affected room, before
treatment, was about fifty milliGauss. The
average flux density after treatment
exceeded ten milliGauss. The monitor
problems remained. Treatment was not a
success. Now, it is obvious that, as a
minimum, comprehensive area shielding,
and significantly greater shielding efficiency,
Ln the vault space itself, was needed.
This experience prompts me to make
two, closing comments on the point of
looking for engineering solutions:
1. Knowing what works and what does
not, and knowing what is cost-effective and
what is not are invaluable for cost avoidance
and project reliability. This knowledge must
come from first-hand experience. Trying to
remedy a major magnetic field problem
without prior experience could result in
repeated, failed attempts and excessive cost.
2. Shield design is the province of the
expert. Design, and probably installation
also, might better be left to a company
which specializes in this work.
* * *
References & End-Notes
1.2.S. For a good explanation of the creation of
magnetic fields and electric field*, and their properties, sea
Engineering Electromagnetics, William H. Hayr. . Jr.
McGraw-Hill Book Company. Also. EPA Publication AQ2-R-
92-009: 'Questions and Answers About Electric and
Magnetic Field*'
3,4. Feychting. M. Anders. A.: Magnetic fields ana
cancer in people neer Swedish high voltage power lines.
IMM-rapport 8/92. Stockholm Insotet for milijomedicin.
Karolinaka institet. Stockholm. Sweden.
5. For a thorough review of (he WHO.IRPA/INIRC
Guidelines and Limitations, see Health Physics Vol. 53,
No.1 (January) pp. 113-122. 199O.
7. Monitoring for exposure assessment is different
than area/home surveillance. Spot measurements are taken
over the day, at waist height, to establish a time weighted
average for the daily exposure. A minimum of 16 readings.
spaced evenly through the day, per personal exposure is
recommended.
8. IEEE Standard 0644.1979. Institute of Electrical
and Electronic Engineer*, New York, NY.
9. Technical Information Office: 650O Glenway
Avenue, building D-7. Cincinnab. OH 45211-4438.
10. The Occupational Hearth and Safety
Administration. OSHA set* occupational standard*. The
General Duty clause may apply when no specific standard
is relevant and a senous recognizable hazard exists.
. Acknowledgment
The test data and work contributions of
my colleagues L. Darveau and J. Cherniack are
acknowledged with pleasure. My thanks to W.
Chenoweth, W. Ho/brook and R. Hinten for
their reviews and comments. Special thanks
go to L Maltin. Amuneal Manufacturing
Corporation, Philadelphia, PA 13124, for
sharing with me proprietary attenuation
information from some of his mitigation
projects, as well as information on material
properties and proven uses.
The author would welcome additional
information on the matters mentioned here •
especially information on mitigation efforts
which have proven to be either successful or
unsuccessful. Norman Beddows, Region 1
Safety, Health and Environmental Program
Manager. United States Environmental
Protection Agency, J.F. Kennedy Federal
Building, Boston, Massachusetts 02203-2211.
(617) 565-3388.
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APPENLOX3
REGION 1 MAGNETIC FIELD SURVEY ASSESSMENT
-------
- UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
f B€C10NI
MDlflAt
To: P. Meaney, Acting Deputy Regional Administrator.
Through: S. Perkins, Deputy Assistant Regional Administrator.
From: N.A. Beddows, CIH, CSP /i*/>— •& . H/.
Regional Health and Safety Manager. "/"' *
Subject: Extremely Low Frequency (ELF) Magnetic Fields in Regional Off.
Information For Use in Addressing Possible Employees' Concerns
A. Consideration of the Pfeseppp of A, Hazard
At the outset, I want to assure you and our employees that there are no t$n
recognizable health hazards related to ELF magnetic fields in any office or work :
in either of the Canal Street or the Congress Street EPA Facilittes.
With respect to ihis assurance, I should explain that occupational exposures to extre
low frequency (ELF; 60 hertz) magnetic fields occur in every office environment.
thcal power sources, power distribution centers, elevator electrical machinery, com
centers, lighting and personal computers generate electromagnetic non-ionizing radia
However, the m»fn«ie component of every electromagnetic Meld from such sour:
weakened dramatically by separation by distance. Such separation by distance ex:
ail of the office layouts employed in the two Boston offices of Region 1 .
J. Cherniack, L. Darveau. R. Hintan and myself were involved in one or more a:
of monitoring (1) magnetic flux densities in offices and researching relevant guide:
Seveni hundred spot measurements of magnetic flux densities in our offices have
measured in the last few weeks by J. Cherniack and L. Darveau, using a Holac;
3627 Electromagnetic Field Survey Meter. I believe that the extent and quality <•,
monitoring used, most of which I either witnessed or identified as required, adeqi
characterizes the referenced facilities.
In the offices in the EPA facilities at Canal Street and One Congress Street, pot
office ELF magnetic (B flux density) exposures span two orders of magnitude. T
evident from the flux density data that J. Cherniack and Linda Darveau have me:
and reported. However, the highest flux density reported for any work station m an
of a station is two orders of magnitude less than the World Health Organ::
International Radiation Protection Association's (WHO/IRPA) Occupational Lien.
for continuous occupancy exposure to ELF magnetic fields (discussed later;.
«•«••» «0 OH
-------
What we have as'.erminea is sufficient to allow me to feel comfortable in cec:ar;nz
there are no known, recognizable hazards associated with ELF magnetic fields ir.
referenced offices. In saying tnis. I realize that data gaps and unansweraoie sues1.
abound on many aspects of this topic.
3. Background Information
As you know, exposure to ELF electromagnetic fields is an emerging public ccr
because cancers have been associated with exposure :n some epidemiologic studies
more significantly, perhaps, the topic has featured recently in the press, teievisio.-
in a few wcll-puolicizcd litigated eases.
Explaining ELF magnetic fields in offices and the significance of measured expc
to employees is difficult in most situations, and it is especially difficult when fac:
emotion generated out )f articles, whether sensational or evenly balanced.
While the media have heightened public -.wareness of issues surrounding
electromagnetic exposures, some underlying factual aspects, which are too Uiff.c
address in a few sound bites, go unrealized. To the point, some studies which
suggested a caneer association with certain ELF electromagnetic exposures were
on indirect assessments of exposure - the types of wiring codes employed in
construction in geographic areas near power lines, et cetera • rather than actua.
measurements of magnetic flux densities in homes. Some studies which sugg
association are at odds with the theoretical basis for establishing the magmtuc;
magnetic field density which could induce a current density in skin and
comparable to those current density levels which occur normally in the body. And
studies made by competent authorities indicate that there is no significant linkage sf.
comparable to the surrogate exposure levels reported in studies which say the op:
It seems fair to say that no one is even sure that weak electromagnetic forces
human health and that there is even greater uncertainty in regard to exposure-
question* with such fields.
C.
After reviewing the technical literature, there are two relevant occupational lirv
to consider: the limitation of the American Conference of Governmental Iru
Hygienists (ACGIH), and the limitation of World Health Organizationxlnterr
Radiation Protection Association (WHOMRPA). The WHOURPA limitation is th
stringent of the two. OSHA has no applicable standard, and its [5(a)l] Gencr:
clause is neither relevant nor applicable.
-------
-3-
Dealing with the WHO/IRPA Occupational Limitation, the following points arc rraac
» The criterion underlying the magnetic flux density-based limitation
predicated on that flux density which may induce a current density in hums
tissue which is comparable to the levels of those which correspond to norm
physiological functioning [reportedly, 10 mA m2].
* The limitation includes a reduction factor of 5. This factor is used to acccu
for the scarcity of relevant human data. As a concluding remark, tr
WHOMRPA limitation is provided with the acknowledgment that enteric
employed does not signify that a human health hazard occurs with the releva
induced current density.
» The WHOMRPA established (ELF magnetic field density) threshold limit vaii
for occupational daily exposure is 0. 5 miiliTeslat.
r Tht wvr Tttlt it tfif tcttfttO tfittmetwiH unit for gttenWng I8f maqnttic ft.
tfwwry, lti$ *rwoy»tf m tnt fatnttftc /ournttt tn4 ay jr«/w«rw-jtrr/*»ff tutnonm
On» Tim fowtt 10.000 $«WM. it is em&Qyrt Herein to factHtanjefennca.
> The rationale stated by (he WHOMRPA Committee for establishing it
limitation has wide support among industrial hygienists and health physicist
» The value of the WHOMRPA-Hmitation is two orders of magnitude less tn;
the threshold limit value (60 milliTeslas) for continuous, daily, whole-be
exposure established by the American Conference of Governmental Industr
Hygienists (ACGIH) in 1992.
I believe that the WHO/IRPA Occupational Limitation is entirely relevant and applies
as an interim guideline for large office environments. Of course, nothing prevents
from establishing a more stringent limit as an interim internal standard. Moreove
attaining a significantly more stringent limit for continuous occupational exposure
achievable without any effort by most office facilities.
D. AiMMTnent Raoonad Spot Mftaitirefncnti of Magnetic Plux_Degsiiy.
An assessment of the reported magnetic flux density data on the 90 Canal Street offu:
all of which have the usual electrical services and electronic equipment, is provided
the following part.
-------
-4-
All the offices' magnetic flux density values fall in the range of 0.03
not* tnat 'in ueev tlm/t of rfw« rtngt /» rwo ortf«/j a/ magnituae
liirttttaen for » attfy 9CGuo*tfar&
Most [95%] of the work stations in both facilities have magnetic fields of £
density values which fall in the range of 0. 1 • 0.5 mjcroTeala.
nQto (hit tho vpptr limit of this rmgo it ihrt* oratn of mtamtua* 6t/ow
WHO'JRPA
15 offices have the higher measured values. However, all have magnetic :
densities which fail within the range of 0.13 • 5.0 ousiaTesla.
not* thtt f/w uffttf Unttt ol thto rtng* it two orders of mtan'tud* o«/ow
Baaed on the matters reported and for the reasons stated above, I believe that there
no irnawn. reco|piMhi« ELF magnetic Meld related health hazards in us office or w
space in either of the Canal Street or the Congress Street EPA Facilities.
B.
There are several related but separate matters that I believe should be addressed at
point. They are:
» What should be the philosophy in regard to providing quality S-h
oceupiable work spaces?
» What should w« establish as a (Regional only) interim internal sundarc
establishing office facilities?
» What engineering and administrative opportunities are there for minim
magnetic fluxes and exposures in the office work spaces?
-------
On the first noint (applicable philosophy). [ believe that in establishing layouts 2
providing ot'fice work spaces one should place employees in optimal quality spaces -.-
rteed to keep in mind thai naturai lighting, even temperatures, low noise level, anti h:
venulaiion rate are very major components of quality) to the best extent possible, and
utilize lesser quality spaces fur minimal-occupancy activities: record-keeping c:mc
equipment storage, and the like. I am not aware of die existence of an employer-duty
any possibly relevant health standard which requires an employer to engage in .
extraordinary research on attenuating ambient magnetic fields (i.e., fields with r*
densities less than 5 microTeslu) for the purpose of minimizing potential exposures
offices. Of course, we might need to do this in iome cases.
note. w« caw/0 mate « ortamtnary avitu*non of rnt feastoimv of wgt/mnng out <*
(fusts in gfffett. This mtgm 6* tntnttf vt*»n tourlous nicrnmtgfiattc Was aoc.
to 09 tfficttng comouttf vtdto unin in icmt offfct locinan* us eoeaars TO ot me cue in a
loctnont tt 90 Can*
On the ^cond poii^ (eatablish^nj a t^egjqn^| peetipmnt exnpsure standard^, we airs;
far exceed {fct-work space quality which is afforded by application of the WHOMR
Umi^uon. We have employed a metallic shielding with apparent marginal success
minimize 'the weak but higher man avenge magnetic fields present in a small numbe:
_fvrtr*'Ay .gcT'cmtf """+ «paff « (n&»* the current situation, I believe that it
Appropriate to base a Regional-only internal standard on the principle of "no sigmfic
deterioration . *
The e«i«tln ranaa of otential magnerie flux danaitv exoures in our fucilitiea as •
The interim Magnetic Field Flux Density , 8-hour, Daily, Occupant-Exposure Stan.
which I am recommending for Region 1 , is:
1. An avenge value of 0.5 microTealm (5 milUGausses) evaluated as an
weighted mean value. And,
2. An upper limit of 3 microTeaUs (SO milliGausses) for S-hour occupancy
In my judgment, these values characterize our current occupied office facilities
respect to ELF magnet flux density.
-------
•6-
Dn the ultimate OQint ( engineering and admini
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION 5
77 WEST JACKSON BOULEVARD
CHICAGO, IL 60604-3590
AU6 2 3 1994 REPLY TO THE ATTENTION OF:
MEMORANDUM
SUBJECT: Region 5 Electromagnetic Field (EMF) Survey
FROM: David A. Ullrich ^
Deputy Regional Administrator
TO: Division and Office Directors
Attached are two copies of the results of the Electromagnetic
Field (EMF) Survey which was conducted in February 1994, by the
Air Toxics and Radiation Branch, Radiation Section, of EPA-
occupied space in the Metcalfe Building. The survey covered
approximately five percent of the non-enclosed workstations,
enclosed offices, copy rooms and kitchenettes on each floor, and
also included unique areas such as the main computer room and the
library. This survey was primarily designed to determine
background EMF levels in the Region.
This EMF Survey provides an excellent profile of the magnetic
field environment in EPA-occupied portions of the Metcalfe
Building. Based on this profile, magnetic field strengths appear
to be on the lower end of the scale for a typical office
building.
A copy should be maintained by your Administrative Officer and be
available to any employee interested in viewing this document.
Attachments
Printed on Recycled Paper
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