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Nowadays, compressed air is used in a huge
variety of applications. It is used as breathing
air in respirators and diving apparatus,
for instance, to enable people to breathe
safely in hostile environments. In hospitals,
compressed air is used not only for the vital
process of ventilating patients during surgery
and in the intensive care unit, but also to
operate surgical tools and for a range of
technical applications.
In industry, compressed air represents a
form of energy whose spectrum of applications
is unrivalled by any other. Without
compressed air, the level of automation
typical of modern factories nowadays would
be unthinkable. Compressed air is used,
among other things, in pneumatic tubes for
transporting items, for remote control of
valves and gate valves, and to operate tools.
Depending on where the compressor is
situated, the ambient air it sucks in may contain impurities such as |
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– mineral oil
vapours |
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– water vapour |
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– particles |
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– harmful substances in gaseous form,
such as carbon monoxide. |
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During the compression process, lubricant
oil and tiny abrasion particles from the compressor
may additionally find their way into
the compressed air. Dust and other particles
increase the extent of abrasion within the
compressed air network and prematurely
wear pneumatic systems. Resinous oil in
the pipeline system may reduce pipe diameters
and cause blockages within the
system. If the water vapour content of the
compressed air is too high, the pneumatic
system may corrode, electrical elements
may form and, at low temperatures, ice
may form within the compressed air network, resulting once again in reduced
diameters and blockages.
Harmful substances in the compressed air
can pose a risk to ventilator patients and
wearers of respiratory protective devices.
In the food and pharmaceuticals industries,
where compressed air may come into contact
with products, particularly stringent
quality requirements apply. For example,
the compressed air must be properly conditioned
for use and its quality monitored
by means of suitable measurement methods. |
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Regulations
Different areas of application require different
degrees of compressed air purity in
order to satisfy the specific requirements.
The quality requirements for the different
uses of compressed air are described in
the standards listed in Table 1. (see pdf-file) |
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Measurement technology
There are various different methods of
testing the quality of compressed air.
Dräger Safety has a range of total solutions
on offer to reflect the parameters needing
to be monitored: |
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– Ready-for-use methods which customers
can use to perform their own tests. |
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– Services provided by the accredited
Dräger Analytical Services, offering
precise measurement results and expert
reports. |
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Test tube measurements
Probably the simplest method of detecting
contaminants in compressed air are test
tubes. Using the Dräger Tubes®
carbon dioxide 100/a-P
carbon monoxide 5/a-P
nitrous gases 0.5/a
oil 10/a-P
sulphur dioxide 0.5/a
hydrogen sulphide 1/d
water vapour 20/a-P
water vapour 5/a-P
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in conjunction with the Dräger MultiTest
med. gases for the monitoring of compressed
air, which is used for medical
applications, or the Dräger Aerotest, which
is used to test the quality of the breathing
air in respiratory protective devices, the
concentrations of the above gases can be
determined (Figures 1 and 2). This method,
with the exception of the oil detection test,
can also be used to test compressed air in the food and pharmaceuticals industries as
required by ISO 8573-6 [4]. The technical
data are summarized in Table 5. |
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If the type of oil used in the compressor
is known, a specific threshold value of, for
example, 0.1 or 0.5 mg/m3 can be selected
when conducting a measurement with the
Dräger Tube oil 10/a-P. If the result of the
measurement is negative, it can be assumed
that the oil concentration is below the chosen
threshold value. In the case of a positive
reading, the oil concentration should be
verified by a laboratory test method. Residual
oil concentrations below 0.1 mg/m3,
such as are required by ISO 8573-1 for
compressed air in general applications,
especially in the food and pharmaceuticals
industries, cannot be checked using this
method. For this purpose the laboratory
test described in a section later must be
applied. |
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Services offered by Dräger Analytical Services
On the basis of the following standards,
Dräger Analytical Services has developed
methods of analysis which can be used to
reliably detect residual oil concentrations –
even in trace concentrations – in compressed
air. |
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Testing the oil concentration in
compressed air for medical use
Determining the oil content of compressed
air for medical use is done on the basis
of the European Pharmacopoeia Ph. Eur.
5.0/1238, "Air for medical use“. This document
requires the air to be decompressed
at the outlet point using a flow control unit
and routed at a flow rate of 20 l/min
through the sampling head, which contains a special filter, for a period of five minutes
(Figure 3). The points of measurement are
determined together with the client. As a
rule, three measureme7nts are conducted
on one pipeline system: |
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Sampling immediately behind the compressor,
drier and filter system; |
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Sampling at a pipeline from which compressed
air is frequently extracted, e.g. in
an intensive care unit or operating theatre; |
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Sampling at a pipeline which is as long
as possible and from which compressed
air is taken only rarely, e.g. in a patient's
room on the ward. |
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At Dräger's analytical laboratory, the filter
is extracted and then measured at three
wave numbers in a Fourier transform infrared spectrometer. The oil concentration is determined
on the basis of the sum of absorptions
and a previously recorded calibration
function. The detection limit depends on
the type of oil in use and ranges from 0.04
to 0.08 mg/m3 for an air sample of 100 litres. |
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Testing the oil content of compressed
air for general applications
In the food and pharmaceuticals industry,
compressed air can only be used if its oil
content (sum of oil aerosol and oil vapour)
meets the requirements of quality class 1
(≤ 0.01 mg/m3). Determining the oil content
in compressed air for general applications
is done on the basis of ISO 8573-1, 8573-2
and 8573-5. The sampling system designed
especially for this purpose (Figure 4) comprises
a glass fibre filter inside a filter cartridge
to enrich the oil aerosols and a downstream
activated charcoal tube for the
adsorption of the oil and solvent vapours. This procedure can also be used to check
the oil concentration in breathing air.
The measurement points are determined
together with the client. The air is decompressed
at the outlet point using a flow
control unit and routed through the sampling
system to enrich the oil aerosols and vapours.
Depending on the quality class
required, the following volumes are routed
through the sampling system: |
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Quality class 1
(max. oil content 0.01 mg/m3)
at least 2500 litres |
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Quality class 2
(max. oil content 0.1 mg/m3)
at least 250 litres |
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At Dräger's analytical laboratory, the oil aerosols
and vapours which have been enriched
on the sample carriers are determined by
means of infrared spectrometry and gas
chromatography. Determining the oil particle fraction is done
by extracting the glass fibre filter using a
solvent and subsequently analysing it by
means of a Fourier transform infrared
spectrometer (FT-IR) in a wave number
range of 2800 to 3100 cm-1 (Figure 5).
The oil vapour and solvent concentration is
determined by extracting the activated charcoal
and then separating it by gas chromatography
on a capillary column using a
flame ionization detector (Figure 6). The oil
concentration (aerosol and vapour) is calculated
as the sum of the two analysis results.
Additional analyses can be performed to
answer specific questions. For example, by
conducting comparative IR analyses of the
air sample and the oil inside the compressor,
it can be determined whether the oil to be
found at the outlet point corresponds to the
oil type inside the compressor. |
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Further services offered by Dräger
Analytical Services
You can engage our accredited and certified
analytical services to analyse your air
samples. As an independent service provider,
we are your professional partner for all
questions relating to air and gas analysis.
The range of services we offer includes |
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free advice on the selection and use of
sampling systems |
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analysis of sampling tubes and systems
used for workplace, indoor air, emission
and immission measurements |
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material testing for volatile contents |
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compressed air testing (including
breathing air and medical-grade air) |
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biocompatibility testing |
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analysis of selected parameters, e.g.:
isocyanates, anaesthetic agents, oil,
amines, timber protection agents, moulds,
solvents of high and medium volatility,
and many others |
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thermal desorption tube analysis by
GC/MS |
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The analyses are performed in line with
recognized guidelines and standards (BG,
DFG, DIN, EN, HSE, ISO, NIOSH, OSHA).
Highly qualified personnel and the use of
state-of-the-art analytical methods ensure
maximum reliability of results. The laboratory
regularly takes part in inter-laboratory tests
and is constantly audited. |
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Dräger Safety's measurement agency,
which is accredited according to DIN EN
ISO/IEC 17025 (reg. no. ZLS-P-598/05),
offers you a complete hazard substance
management service. Our services include
consulting, measurement planning, sampling
and on-site measurements, analysis of samples and assessment of results in the
form of a measurement report or expert
report. |
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For further information about the range of
services on offer from Dräger Analytical
Services, please visit our website at
www.draeger.com
Karl-Heinz Pannwitz
Dräger Safety AG & Co. KGaA
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