Building a Nano-Friendly Facility
With the increasing emphasis on research and development in nano-scale subjects—including
nanomedicine, nanofabrication, and the imaging of nano-scale structures in bioengineering,
proteomics/genomics, and other emerging fields—facilities must be planned and
designed to meet the complex physical requirements of highly sophisticated imaging
and analysis equipment while efficiently meeting the needs of the scientists who
use these instruments. In particular, the use of MRI, NMR, and SPECT-CT instrumentation,
and the installation of nanofabrication clean suites raise challenging planning
and design issues, including space planning, structural capacity, vibration and
noise isolation, magnetic and radiofrequency shielding, and instrument quench
exhaust. Here is a look at the issues and practical solutions.
Increasingly powerful MRIs
Nanomedicine research is one of the factors that has led to the evolution
of more powerful MRIs, placing greater demands on facilities design. In particular,
the evolution of more powerful magnets (where 1.5 tesla once was the norm, MRIs
can now be 12 tesla) has created special requirements.
Photo of a technician performing an
MRI scan on a patient in N.Y.’s Buffalo General Hospital. Photo: Patricia
Layman Bazelon |
First, the MRI suite requires careful facility space planning. Commonly these
suites require an area of 92.9-m2 or more, comprising a 46.4-m2 instrument room,
23.2-m2 dedicated machine room and 13.9 to 18.5-m2 dedicated control room.
Structural engineering must take into account the weight of the instrument, which
may exceed 4,535 kg. Today, a typical 13-cm thick poured concrete slab on grade
is inadequate; successful installations require a 30 to 60-cm reinforced concrete
slab. Therefore, the instrument ideally is placed on the ground floor or basement
of the facility, which, in turn, further affects space planning.
Today’s MRIs typically require steel shielding to contain their strong magnetic
field to prevent demagnetization of pacemakers, credit cards, etc., and to prevent
objects made of ferrous metals from being drawn into the instrument. In addition,
the structure of the building containing the instruments must be designed to prevent
the transfer of noise from the MRI room to adjacent spaces. Typically this is
achieved using staggered double-stud, insulated walls or by providing double walls
with air gaps between walls; extending walls to the structure; as well as utilizing
isolated slab design within the MRI instrument space and designing in-duct sound
traps.
Copper radiofrequency (RF) shielding must be employed to prevent interference
with the operation of the instrument by external RF waves and shielding must be
extended to include air handling ducts, pipes, and conduits. The instrument must
be isolated from the sources and effects of vibration, including elevators and
street traffic. This is achieved by effective location of the room within the
building, a heavier, isolated slab, and use of isolators on the magnet itself.
Finally, the magnet room must be designed with an effective, rapidly acting emergency
quenching exhaust system in case of an unexpected, rapid loss of the super cooling
media of the instrument, typically liquid nitrogen and helium under pressure.
Designing for NMR imaging
More and more research facilities are being designed to house state-of-the-art
nuclear magnetic resonance (NMR) instruments to facilitate three-dimensional imaging
of the physical topology of genes, proteins, and other structures. Over the past
20 years, the R&D world has observed the evolution of NMR from 300 MHz to 900
MHz, and everybody is talking about “the next level.” Typically, at each successively
greater power level of instrumentation, the result is clearer data, allowing more
precise imaging.
NMR instruments require careful space planning. In particular, planning must take
into consideration both the horizontal and vertical magnetic field of the NMR
instrument, starting from the basic question of whether the researcher is planning
on a “self-shielding” instrument or a non-shielded instrument. If the instrument
is self-shielded, its physical size is much larger, but its external magnetic
field is contained within its perimeter. Non-shielded magnets are physically smaller,
but their potentially hazardous, strong magnetic fields may have radii of 3 to
4.6 m or more surrounding the instrument. Safe containment of the magnetic field
above the 5-gauss limit for an unshielded NMR instrument requires provision of
a large open space of up to 7.6 m in dia around the magnet or, in some cases,
heavy steel plate shielding around the perimeter of the instrument room including
the ceiling.
Depending on the power of the instrument, the vertical field may extend 2 to 3.6
m above and below the magnet. Thus a minimum 5.4-m floor-to-floor height may be
recommended to isolate the magnetic field from overhead ductwork and other building
systems, as well as to prevent intrusion of the magnetic field into occupied labs
on the floor above. A cost-effective solution is to place the magnet in a pit
excavated below the ground floor to gain more height at the location of the magnet.
Of course, an alternative may be to purchase a self-shielded instrument.
Sufficient radio frequency isolation for NMR instruments is generally less of
an issue than it is for MRI instruments because the NMR can be shimmed to compensate
for potentially disruptive environmental RF sources. Generally a 15- to 20-cm
thick, isolated slab on grade may be sufficient, unless the facility is subject
to significant vibration. Nevertheless, the instrument suite should be located
away from corridors, streets and elevators, and other pathways of large, moving
metal parts.
A technician examines a cryostat apparatus
on an 800 MHz NMR instrument located at the Univ. of Kansas Structural Biology
Building in Lawrence. Photo: Courtesy of Gould Evans, Photography by Michael
Spillers Photography. |
Other instrument requirements
SPECT-CT, ultrasound equipment, and gamma cameras are instruments that have less
intensive planning, design, and construction requirements:
• Location of a SPECT-CT is fairly flexible, but cost-effective space planning
locates this instrument proximate to other instruments requiring a thicker concrete
slab.
• Ultrasound equipment requires more power and data outlets.
• Gamma cameras should be located within the radiochemistry lab or in an adjacent
room. These require lead shielding of the walls and doors from floor level to
about 2 m.
All of the spaces described above require seamless vinyl flooring to prevent migration
of spills.
It is worth mentioning that use of focused-ion-beam instrumentation is sometimes
a consideration in R&D facilities. These instruments have the greatest vibration-proofing
requirements. In practice, they may require a 60-cm separate slab on the ground
floor, which is isolated from the rest of the slab, and a dedicated pier that
extends to bedrock below the facility. Therefore, facility owners would do well
to plan new facilities to accommodate this technology if there is a reasonable
chance it will be introduced in the future.
Core lab planning and design
In general, planning of today’s R&D facilities must balance cost with user convenience.
The more precise the instrument, the more important it is to have a vibration-resistant
environment. Therefore, a basement or ground floor tends to be the least expensive
place to locate MRI, NMR, and SPECT-CT instruments. However, these have now become
core labs for R&D activities of many scientists across many disciplines. Thus
researchers increasingly demand core labs to be proximate to their primary research
labs, that is, distributed throughout the building, rather than only on the ground
floor.
A cost-effective solution requires identification of a “core zone” through the
building, stacked vertically, with a heavier structural design, for example, four
structural bays in the core of the building that are controlled to a 1,000-microinch
level, with the remainder of the building controlled to a 2,500-microinch level
or less, as appropriate.
Special needs of nanofabrication
Clean room environments for nanofabrication activities, whether they are Class
100, 1,000 or Class 10,000, have special requirements. In nanofabrication facilities,
space planning for the sequential move from lower to higher cleanliness levels
and vibration control are key issues. Prefabricated, pre-engineered 3.3- to 4.2-m
tall clean-room suites with built-in air handling and air filtration capabilities
are often utilized in R&D facilities to allow maintenance of clean environments.
Ideally, facilities which house these components should provide for a minimum
5.4 to 6-m floor-to-floor height to allow all the building systems to pass overhead
and still maintain access to the clean suite plenum from above. Moreover, the
structure should be designed to control vibration typically in the 1,000 microinch
or lower range. Therefore, an isolated slab on grade condition may be ideal, away
from vibration sources such as elevators or mechanical rooms.
Today’s focus on nanotechnology requires effective facility planning and design
to meet the physical needs of precision instrumentation while balancing issues
of user convenience. As in all R&D facilities planning, it is critical that the
design team—from lab planners to architects and engineers—review the operating
parameters and location of the owner’s proposed instrumentation and activities
carefully with the owner. Then a proper cost-benefit analysis of the potential
provision of highly-controlled environments for the instrumentation can be carefully
assessed with the owner from a mutually-informed viewpoint.
Thomas Harvath,
AIA Principal Science Technology Practice, Cannon Design
Punit Jain,
LEED Associate Vice President, Cannon Design
|
