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Up until the 1970s, creosote was used in
buildings, one of its purposes being to provide
protection against damp. Nowadays it is
known that creosote releases carcinogenic
and odour-intensive substances, yet many
contaminated buildings are still in use today.
This article will present an example of successful
decontamination in which accompanying
air analysis and analysis of the
various building materials proved indispensable.
In the year 2000, the Swiss Agency for
the Environment, Forests and Landscape
(BUWAL) issued a warning concerning
the presence of carcinogenic substances in
creosoted railway sleepers. The sleepers
had been soaked in creosote which contains
highly odorous and carcinogenic substances.
Analyses conducted by the Swiss testing
institute Empa have revealed that even after
25 years two-thirds of the creosote still
remains in the sleepers and is constantly
evaporating or leaching out. Up until the
1970s, creosote was also used in buildings
as a means of protecting floors from damp,
and as a timber protection agent. Mouldy
and unpleasant odours often bear witness
to the application of such applications. Experience
in the field of chemical indoor air
analysis shows that the air concentrations of
these harmful substances remain unchanged
over decades, meaning that there can
be no reduction in the concentration unless
decontamination measures are undertaken,
i.e. unless the source is removed.
Experience still lacking
In many cases, the carcinogenic effect of
creosote and the odour pollution it causes
result in the decision to undertake decontamination.
Unlike with asbestos and PCB,
where decontamination procedures are well
established and have passed the test of
time, there is still little experience available
in the area of cleaning up buildings contaminated
with creosote and disposing of contaminated
building materials. For one thing,
the high toxicity of the substances and the
risk that ceilings and floors could become
contaminated when building waste containing
creosote is removed demand increased
protective measures to be taken with respect
to both the building and personnel.
Air analyses can be performed to assess
which protective measures are necessary.
For another thing, the high proportion
of odorous substances and the special
way that building waste contaminated by
creosote reacts to fire means that particular
requirements have to be met as regards
disposal, ruling out normal waste disposal
or incineration in waste incineration plants
or cement factories. One argument against
landfill dumping is the large proportion of
highly water-soluble compounds, while incineration
in cement plants is not an option
due to the high proportion of odorous substances,
and incineration in conventional
waste incineration plants is not possible
on account of the material's viscosity.
Difficult to achieve one hundred
percent decontamination
The first priority when dealing with odourintensive
substances is to remove their
source. Even the tiniest residues of harmful
substances can endanger the success of the
decontamination process. As we have seen
from the example of the railway sleepers,
creosote is still able to release harmful
substances into the ambient air even after
many years and a constant air flow. The
complete removal of the harmful substances
in practice, however, especially in the case
of creosote, poses major problems. In many
places, creosote was spilt on the ground,
and as a result has seeped over the years
into concrete and walls to a depth of up to
20 centimetres.
Often the building's supporting elements
were contaminated, meaning that a complete
removal of the source is virtually impossible
and consideration has to be given
to sealing measures.
There are a number of products available
on the market for sealing buildings against
harmful substances, but not all meet the
practical requirements of the building industry.
Besides providing a reliable seal against
the odorous substances, they need above
all to be easy to apply and guarantee leak
tightness even on pipes, wires, sills etc.
In this case, better results are achieved by
means of casting than with composite films
lined with aluminium. It is very difficult to
seal pipe connections using composite films,
yet many casting processes have not been
tested with respect to their contaminant
retention capacity, meaning that only limited
statements can be made about the longterm
success of such methods.
Analytical methods to accompany
decontamination
Objective evaluation data are needed to
ensure that the correct measures are initiated
in decontamination projects, which can
frequently prove very expensive.
One reliable and sensitive method of analysing
volatile organic components is gas
chromatography with mass selective detection.
Thermal desorption technique is used
to collect samples. This method can be used
to analyse both air and material samples,
and has been established for some years
now at Dräger's Analytical Services laboratory.
The advantages of the low detection
limits and wide substance spectrum, encompassing
a wide boiling range (especially
high-boiling components like naphthalene
compounds), are of great significance, particularly
in this application example.
Thermal desorption tubes (filled with Tenax
TA) are used for air sampling on site.
These are reusable sampling tubes which
are stored in air-tight containers rather than
being sealed by melting. |
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The sampling process can be done using
pumps such as the Dräger Accuro or
Quantimeter. A sampling volume of just
three to five litres is sufficient to be able to
reliably detect naphthalene concentrations
right down to the lower μg/m3 range. At the
same time, short sampling times are also
possible. The chromatogram shows clearly
the significant proportion of naphthalene
compounds as a percentage of the total
contamination of a room.
From the results of the air analysis, it is
clear which rooms are contaminated. To find
out which materials may be possible contaminant
sources in these rooms, samples
were taken from suspicious building materials.
In the laboratory of Dräger Analytical
Services, direct thermal desorption was used
to analyse the various material samples.
This method involves thermally desorbing
the weighed out material at an increased
temperature and transfering the desorbed
substances to the GC system. The emitted
substances are focused in a cold trap and
then analysed by gas chromatography
with a mass selective detector. Even the
tiniest sample quantities are sufficient for
this method. The contaminant source can
be clearly identified on the basis of the
chromatograms (as in Figure 2, for
example). In this way, the source can be
individually removed and any secondary
emission sources identified.
Practical testing of casting processes
When a schoolhouse needed to be decontaminated
in the city of Zurich, a casting
process was applied and the necessary
accompanying measurements performed.
Generally speaking, the nose is the best
way to assess odour intensive substances
such as the naphthalene to be found in
creosote, as its smell can be perceived even
at low concentrations in the microgram
range. This is also the case when it comes
to locating contaminant sources. Nevertheless,
indoor air measurements represent a
useful method of objectively and quantitatively
assessing the progress of decontamination
activities. A person's sense of smell
is greatly impaired and distorted when exposed
to the sort of high solvent concentrations
which typically occur at building sites.
In this respect, chemical air analyses show
themselves to be a low-cost, robust and
reliable alternative.
The measurements conducted during the
course of the schoolhouse decontamination
showed that the casting process was able
to significantly reduce the concentrations
in the ambient air of the contaminants
naphthalene, diphenyl and dibenzofuran
contained in the creosote. However, before
the main contaminant sources can be removed,
the rooms in question have to be
stripped back to the bare brickwork.
The next step, which involved sealing the
floors, reduced the contaminant concentration
by somewhat more than half (see Figure
3: bar marked "after decontamination").
The seal was improved in a second step,
adapted better to the pipe connections,
among other things, and extended to include
the base area. This considerably
improved the success of decontamination,
as the third bar in the graph shows.
Decontamination goal achieved
Since these measures were able to achieve
the decontamination goal – that the substances
should no longer be present in
harmful concentrations nor should their
odour be perceptible – the shell of the building
was then approved for the construction
phases I and II. Once all the decontamination
work had been completed, another air
analysis was performed.
This showed for one thing that the jointless
floor, floor coverings and mineral plaster
have no additional sealing effect because
the contaminant concentration was hardly
reduced as construction work continued
(see fourth bar in Figure 3). For another
thing, the casting method proved to be very
good in the short term, i.e. two months after
the sealing process. The first leak tightness
tests conducted six months after the end of
the construction phase also showed positive
results (see fifth bar in the graph in Figure
3, marked "6 months after end of construction")
and would lead one to assume a
good long-term result of the chosen variant.
Conducting air analyses to accompany
decontamination measures also showed
clearly that extensive decontamination work
can fully eliminate the diphenyl and dibenzofuran.
In the case in question, the odour
intensive naphthalene was reduced by a
factor of 10, thus bringing it down to below
the odour perception threshold. It was not
possible to eliminate it entirely, however,
because the remaining contaminants rise
up inside the walls and are released by
diffusion into the room. A glance at similar
decontamination projects in Germany, however,
shows that other methods of decontamination
are only able to achieve a factor 2 to
5 reduction in the contaminant concentrations.
Quality of construction work is crucial
Successful decontamination of odour intensive
contaminants can be achieved, in other
words, by more or less completely removing
the sources and sealing surfaces by means
of casting. However, if contaminants have
been allowed to spread throughout a building
over a longer period of time and have
penetrated the walls, complete elimination
will prove difficult. By implementing additional
improvements and optimizing the seal
in critical areas, the contaminant concentrations
were reduced again by a factor of
three.
This shows that the decontamination of
odour intensive substances places the
highest possible demands on the quality of
the construction work and the choice of
materials.
Philipp Thalmann und Reto Coutalides
Beratungen + Messungen AG
www.raumlufthygiene.ch
Dirk Rahn-Marx
Dräger Safety AG & Co. KGaA
www.draeger.com/analysenservice
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Dräger Safety AG & Co. KGaA |
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Revalstrasse 1 |
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23560 Luebeck, Germany |
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Tel +49 451 882 0
Fax +49 451 882 2080
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