Microbes and Boulders
Barbara Kanegsberg and Ed Kanegsberg, August 2004
Hospitals in the United States must supply medical air that meets established
standards for cleanliness.1 Dental offices, too, endeavor to provide clean
air. Accordingly, much effort is invested in the design of medical air systems.
By design, on-site compressor systems deliver air that is oil-free. The dew
point is maintained sufficiently low to prevent microbial growth. Downstream,
there is generally a filter to remove particles down to one micron.
However, prompted by concerns about the possible presence of biological-based
contamination in compressed air,2 researchers at SUNY Buffalo (see Endnote)
started a study to investigate the possible presence of microbes and/or biofilm
fragments in air delivered at six facilities, five hospitals, and one dental
school.
The good news is that the medical air at all locations was free of microbes.
However, as with biomedical devices,3 one need be concerned with contaminants
both alive and dead. SUNY researchers looked beyond the microbes.
Air from all locations contained inorganic particles of up to 100 micrometers,
boulders for biomedical applications. Further investigation indicated
that large particles were mostly agglomerations of smaller particles,
some containing
tin, copper, potassium, calcium, chlorine, bromine, iron, lithium, zinc,
aluminum, magnesium, silicon, and a few other elements. The current hypothesis
is that
a likely source of contamination is downstream of air purification and
filtration systems. After final filtration, the cleaned air passes through
copper tubing.
A former graduate student, who had worked his way through school as a
welder, provided technical references that offered clues that the
observed contaminants
are consistent with residual flux that may be present in welding or brazing
copper tubing.4
There is concern that the observed contaminants are chemically active,
and may continue to be generated (as in the formation of "tin whiskers" in
soldered electronics). Such activity is useful in the initial welding process.
However, whenever one has an active element, steps must be taken to restrict
the presence of that element; as even small amounts may produce significant
contamination.
In addition, in cases where such systems supply air to manufacturing
operations — such
as in pharmaceutical processing — these contaminants could interfere
with assembly processes.
The study provides an illustration of contamination from sources
not initially considered to be a problem. Contamination from transfer
lines
is not unheard
of in other applications. For example, in dispensing bulk solvent
to small containers, transfer lines can be a contamination source
if residue
remains
from previous dispensing operations or if materials of construction
are inappropriate and dissolve in the solvent. On occasion, plasticizers
detected on a surface
have been traced back to the nozzle or tubing of aerosol containers.
The question then arises as to what is an adequate cleaning process
for brazed copper tubing. The process must not contribute to
corrosion and
it must not
produce a surface that would degrade or continue to generate
particles. An additional filter might be added at the end of the
system. However,
sufficient
flow of air would have to be maintained for adequate functionality
including respiratory equipment, dental procedures, and manufacturing
processes.
If one sets out to look for biological contaminants, one may
or may not find them. A more comprehensive set of observations
from
the
SUNY study
appears
to have significant implications for biomedical facilities
and perhaps for high-value, critical manufacturing processes. Results
of the
initial study
will be submitted to a peer-reviewed journal, and additional
sampling will be conducted. In addition, because results may
be climate-dependent
(some
earlier reports of contaminated and/or corrosive air in gas
meters
and in automotive
systems were predominantly in humid areas), sampling may include
facilities in warmer climates with higher humidity.
Note: This article was written by Barbara Kanegsberg and Ed
Kanegsberg along with Robert Baier, Prashant Nagathan, and
Tamara Brown.
Dr. Robert Baier
is Professor and Executive Director, Center for Biosurfaces,
SUNY Buffalo; Prashant
Nagathan is an MS student in Mechanical and Aerospace Engineering
at SUNY Buffalo; Tamara Brown is Project Manager for Healthcare
R&D at Praxair, Inc.
References
1 NFPA Standard 99c, Gas and Vacuum Systems, 5.1.3.5, Quality
of Medical Air.
2 P. Bjerring, B. Oberg. "Bacterial Contamination of Compressed Air for
Medical Use," Anesthesia, Vol. 41, (1986) pp. 148-150.
3 Kanegsberg & Kanegsberg, A2C2, (April, 2003 and July, 2004).
4 Soldering Manual, American Welding Society, 33 West 39th
Street,
NY, NY
Barbara Kanegsberg
and Ed Kanegsberg are independent consultants in critical cleaning, precision
cleaning, surface preparation, and contamination control. They are the
editors of “Handbook for Critical Cleaning,” CRC Press. Contact
them at BFK Solutions LLC., 310-459-3614; info@bfksolutions.com; www.bfksolutions.com.
