HSL/2000/22: Assessment of exposure to light mineral oil based metal working fluids

94 Pages·2007·1.78 MB·English

Harpur Hill, Buxton
Derbyshire, SK17 9JN
T: [phone]
F: [phone]
W: www.hsl.gov.uk

Assessment of Exposure to Light Mineral
OilBased Metal Working Fluids

HSL/2000/22
Project Leader: Andrew Simpson

Author(s): Andrew Simpson BSc

Science Group: Environmental Measurement Group

© Crown copyright (2000)
Summary
Objectives
To investigate methods for measuring exposure to light mineral oil based metal working
fluids.
Main Findings
The current HSE method cannot be used for measuring oil mist from metal working fluids
based on light mineral oils. Standard filter sampling is unsuitable because volatile
components in the oil collected on the filter may be lost by evaporation during sampling,
resulting in an underestimation of the true mist concentration. During this work it was also
found that;
w There can also be substantial losses during storage and in the equilibration period
before gravimetric analysis.
w The loss of sample material can be reduced by refrigerating the filters during
storage and reducing the equilibration time before gravimetric analysis.
w Immediate solvent desorption after sampling for subsequent analysis by Infra Red
spectroscopy would also reduce losses.
Nevertheless evaporation during sampling is still likely to occur. Alternative methods were
investigated for measuring total airborne oil (mist and vapour) and for measuring the vapour
alone.
Total airborne oil can be sampled by a combination of a filter sampler (to collect mist) with a
vapour sampler situated behind it (to sample original vapour and vaporised oil from the filter).
The measurement of total oil should be more accurate than a measurement of only the mist as
there should be little overall sample loss. It should be applicable to all mineral oil based metal
working fluids. A number of types and combinations of samplers were considered, and the
findings were;
w The conical inhalable sampler provides better splash protection for filters than the
multi orifice sampler and is more compatible with the flow rates of commercially
available sorbent tube vapour samplers.
w The preferred sorbent is XAD-2 because of its superior solvent desorption
properties with perchloroethylene and, unlike charcoal, its capacity for sampling
hydrocarbon vapour is not affected by humid atmospheres.
w In Germany the BIA (Berufsgenossenschaftliches Institut für Arbeitssicherheit)
have a purpose designed system for sampling oil mist and vapour called the
Gesamtsstaub-Gas-Probenahme (GGP) system. It has a conical inhalable sampler
combined with a large sorbent cartridge. The cartridge has a higher capacity for
trapping analyte than commercial sorbent tubes but requires time consuming
preparation involving much contact with perchloroethylene.
w The preferred sampling method is collection at 1 litre/min using a combination of
the conical inhalable sampler with a 8 mm diameter XAD-2 sorbent tube, which
can measure 8 hour samples between 0.1 and 33 mg/m³. An alternative
arrangement, sampling at 2 litres/min using the more common multi orifice
sampler connected to a 8 mm diameter charcoal tube is acceptable and can
measure 0.1 to 83 mg/m³.
w Split flow pumped sorbent tubes were assessed as filter back up samplers but did
not offer any advantages over full flow sorbent back up tubes for oil mist, being
more complicated to set up and not performing as well.
w Diffusive Radiello samplers were assessed as filter back up samplers but were
found to be not at all suitable due to the wide range in diffusive uptake rates of
the various oil vapour components. Other diffusive samplers, such as Tenax ATD
tubes may work as filter back up samplers but were not included in this work
Analytical methods for quantifying the sample material collected were also investigated;
w The preferred analytical method for both filters and sorbent is Infra Red
spectroscopy using perchloroethylene as solvent. Gas chromatography can be
used for sorbent samples and will provide some compositional information,
separating components more or less by their boiling point, but it is not suitable
for filter samples due to possible volatility problems with some potential
components in metal working fluids.
w Any hydrocarbon solvent vapour sampled with the oil vapour will bias Infra Red
measurements, and solvents with boiling points greater than ~170°C such as
white spirit and kerosene will affect gas chromatographic analyses.
w Integral area or a combined peak absorbance of the methyl and methylene carbon
- hydrogen bond stretches are better Infra Red measurements than the single
methylene carbon - hydrogen bond stretch for quantifying oil.
Most of the methods considered for sampling total oil collected the inhalable fraction of the
aerosol, ensuring that samples collected would be comparable with exposure limit values, and
collected the mist and vapour separately. Consideration was also given to sampling both mist
and vapour directly onto a pumped sorbent tube to see how well it compared, despite its
poorer particle sampling characteristics;
w In limited circumstances pumped sorbent tubes could be used to indicate total
airborne oil concentrations. Atmospheres would need to comprise of oil vapour
concentrations considerably greater than the mist concentration. They are
unlikely to be suitable for oils with viscosities much greater than 5 cSt at 40°C or
flash points greater than 140°C.
w Samples were collected at 200 ml/min on 8 mm charcoal tubes and analysed by
Infra Red spectroscopy. The substitution of XAD-2 for charcoal as sorbent would
improve accuracy at low concentrations. Wider apertures and appropriate flow
rates may improve their particle sampling characteristics.
Measurement of oil vapour was investigated as it was seen as a way of obtaining the true oil
mist concentration from a total airborne oil concentration;
w Limited work suggested that oil vapour concentrations could be estimated in the
presence of oil mist by standard diffusive sampling onto Tenax ATD tubes and
analysis by thermal desorption - gas chromatography - flame ionisation detection.
Tests found that although there was evidence that oil mist particles impacted, and
oil vapour condensed on the internal walls, it may be possible to correct for the
bias.
Two types of sampler were evaluated in field trials; the conical inhalable sampler with 8 mm
XAD-2 sorbent back up tube, and lone pumped 8 mm charcoal tubes.
w The filter-XAD tube combination performed relatively well in the tests and
generally gave higher results than the pumped charcoal tube.
w The presence of vapour from mineral spirits in the work place air invalidated
some of the vapour samples. Whilst sampling for oil mist and vapour, it is
important that the presence of interferents such as hydrocarbon solvent vapour
are identified and avoided.
Main Recommendations
w Mineral oil mist and vapour should be sampled using pumped filter samples backed by
sorbent tubes, the most appropriate combination being the conical inhalable
sampler coupled with a 8 mm XAD-2 sorbent tube or alternatively the multi
orifice sampler coupled to a 8 mm charcoal sorbent tube.
w Both filter and sorbent samples should be analysed by Fourier Transform Infra
Red spectroscopy of the perchloroethylene extracts, measuring the combined
peak absorbances of the methyl and methylene carbon - hydrogen bond stretches.
It would be useful to further characterise the method and its limitations by
w Determining the capacity of XAD-2 and charcoal sorbent tubes for oil vapour,
and looking at the effect of high humidity on charcoal sorbent tube capacity.
w Looking at the effect of different base oils (e.g. naphthenic 60 solvent pale),
additives (e.g. chlorinated paraffins), and mist types (i.e. condensation mists).
The applicability of the method could be further investigated by
w Looking at synthetic lubricants (e.g. poly-alpha-olefins and polybutenes) and
mineral oil free non aqueous lubricants (e.g. esters such as rape seed oil).
w Further investigate the mist - vapour phase relationship, including filter sample
losses, by sampling aerosols of oils with varying composition, and by
investigating a wide range of potential additives.
Confidence in the quantification of diffusive samples of semi-volatile aliphatic hydrocarbons
would be strengthened by
w Looking at naphthenic oils, non mineral oil lubricants and additives.
w Re-examining the problem of background subtraction for additional sampled oil,
with the inclusion of work on condensation mists.
w Investigating the effect of multi component mixtures on uptake rates.
Further investigation of the effect of sampler design and flow rate on the particle sampling
characteristics of sorbent tubes could provide simpler methods for sampling aerosols which
contain significant quantities of volatile components, not just for a limited number of mineral
oils but also for drilling muds and other semi-volatile compounds.
If measurement of total airborne oil is seen as an option to be explored further, it is
recommended that HSE should aim to conduct a short survey to gain information on
occupational exposure to oil mist and vapour from the light mineral oil metal working fluids
not included in the recent Technical Development Survey.
Contents
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Reference Method - Conical Inhalable Sampler
Connected to Three Impingers in Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2. Gesamtsstaub-Gas-Probenahme (GGP) Sampler . . . . . . . . . . . . . . . . . 5
2.1.3. Conical Inhalable Sampler Combined with Sorbent Tube . . . . . . . . . . . 5
2.1.4. Multi-Orifice Sampler Combined with Sorbent Tube . . . . . . . . . . . . . . . 5
2.1.5. Multi-Orifice Sampler Combined with Sorbent Tube in a
Split Flow Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.6. Conical Inhalable Sampler Combined with Radiello Tube
Diffusive Sampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.7. Pumped Charcoal Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.8. Diffusive Perkin Elmer ATD Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Test Atmospheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1. Oil Mist Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2. Hydrocarbon Vapour Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. METHOD DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Investigation of Filter Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2. Investigation of Analysis by Infra Red Spectroscopy . . . . . . . . . . . . 12
3.2.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3. Investigation of Analysis by Gas Chromatography -
Flame Ionisation Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.4. Investigation of Diffusive Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.4.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.4.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.4.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.5. Analysis of Factors Effecting Vapour Sampling on
Sorbent Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.5.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.5.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.6. Investigation of Sampling Total Airborne Oil by Lone
Pumped Sorbent Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.6.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.6.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.6.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.6.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4. METHOD EVALUATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1. Laboratory Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.1.2. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.1.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.1.4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.2. Method Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3. Field Trial Visit 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.1. Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.3.3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.3.4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.3.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4. Field Trial Visit 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4.1. Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.4.2. Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.4.3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.4.4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.4.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6. APPENDIX A: INSTRUMENTAL CONDITIONS . . . . . . . . . . . . . . . . . . . . 69
7. APPENDIX B: ANALYTICAL RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
8. APPENDIX C: OIL MIST CHARACTERISTICS AND
PROPERTIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
9. APPENDIX D: WIND TUNNEL RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . 81
10. APPENDIX E: TEST SAMPLER FIGURES . . . . . . . . . . . . . . . . . . . . . . . 84
1. INTRODUCTION
The measurement of mineral oil mist derived from metal working fluids (MWF) has generally
been viewed as a simple task of collecting the airborne mist on a filter, recovering the oil
from the filter followed by measuring the mass of oil. HSL (Simpson 1995) investigated this
technique with the objective of better defining the procedure and evaluating the benefits of
different measurement methods for mineral oil mist. During project R48.084, it was shown
that some neat MWF contain components (mostly hydrocarbons) which are semi-volatile at
normal temperatures and would be expected to have an associated vapour.
While the standard measurement procedure is adequate for 'non-volatile' oils, it can be
expected to be deficient for the lighter, more volatile oils because:
v oil droplets collected onto the filter can be expected to lose some mass by evaporation
as air is drawn through the sampling medium leading to an underestimate of exposure
to mineral oil mist;
v there may be further losses of volatile components during transportation of the
samples to the laboratory for analysis, and
v there may be a substantial vapour exposure problem in the workplace which is not
quantified by the usual measurement method and which will not have been taken into
account when investigating health effects.
An approximation to identify those oils where there may be sample loss during collection was
proposed in HSL's study. This was that MWF with a viscosity above 18 cSt (measured at
40°C) or flash point greater than 180°C can be sampled onto a filter without significant
evaporative loss. At lower viscosities or flash points, oils will have an increasingly volatile
composition and the associated vapour concentration could become significant.
A recent survey by the British Lubricants Federation (BLF) revealed that about 60% of neat
oils used have viscosity less than 18 cSt, and 46% are amongst those most seriously affected
(2 to 6 cSt). Any attempt to apply the usual measurement method to such oils could produce
exposure estimates which are serious underestimates of actual exposure to oil mist. Thus it is
clear that exposure to a significant proportion of MWF cannot be adequately monitored with
the existing techniques and so the true exposure of a substantial number of workers remains
unknown.
There have been some attempts at designing novel samplers to reduce the rate of mist
evaporation, such as personal electrostatic precipitators (Leith et al, 1996) and others for
distinguishing particulate organics (and vaporised particulate) from original organic vapour
by differential inertia (Xiong et al, 1998), but such devices are as yet highly specialised and
not widely available. They also may not have the required particle sampling characterisitics.
The physical characteristics of these oils will always make the possibility of vaporisation of
some material inevitable. Direct reading light scattering devices for monitoring particles may
give some indication of levels but due to variation in oil mist particle size distribution they
can experience calibration problems (Volckens et al 1999).
1
Oil mist is considered to be of much greater concern than the accompanying vapour. The mist
is considered to be more potent than the vapour because the vapour is thought to be exhaled
with little uptake by the lungs due to the low water solubility of the oil, whereas the mist can
be deposited on the walls of the lungs as droplets allowing time for the oil to be cleared from
the lungs (and ingested) or absorbed into body fluids. Consequently analysis has generally
been of the mist only, with the intention of sampling the mist without any evaporative losses,
and collecting no vapour. However once oil mist enters the lungs it will be heated to body
temperature, which will result in further evaporation of semi-volatile components, the
magnitude depending on the oil composition. It follows that even if the original airborne mist
concentration could be measured it would not necessarily be proportional to the oil (and
additives) that may impact on the lung walls for the lighter oils.
One way to get around the problem of sample vaporisation from the filter would be to collect
mist and vapour simultaneously by placing a vapour sampler behind the filter sampler. Any
material lost from the filter would still be included in the sample. The filter and vapour traps
could be analysed separately, giving a reliable mist result for heavier oils comparable with
historical data, and a minimum value for lighter oils. A total airborne oil result would provide
a more general measure of personal exposure to the oil. For light oil mist samples, measuring
total airborne oil accurately should be as good as poorly estimating the oil mist concentration
alone.
A review by HSL (Simpson 1997) investigated the practical problems likely to be
encountered in measuring exposure to volatile MWF. The principal aim of this current work
is to investigate potential methods for measuring exposure to both mist and vapour. This will
involve combinations of filter samplers and back up vapour samplers. Combining filter
samplers with vapour samplers is problematic because the two have conflicting flow rate
requirements. Inhalable filter samplers require precise, high flow rates to enable them to
capture the required particle size range. Sorbent tube type vapour samplers are recommended
for use at lower flow rates, higher flow rates can reportedly cause channelling in the sorbent
and there are implications on capacity and breakthrough due to migration of analyte through
the tube. High flow rates through sorbent tubes will also increase the demands on the sample
pump used to collect the sample.
One method, identified in the review, already exists for measuring total oil (Pfeiffer et al,
1996). It uses a sampling device developed by the BIA (Berufsgenossenschaftliches Institut
für Arbeitssicherheit - Professional Associations' Occupational Safety Institute) in Germany
called Gesamtsstaub-Gas-Probenahme (total dust and gas sampling - GGP) which combines a
conical inhalable sampler (CIS) (described in MDHS 14 (HSE, 1997a)) with a very large
sorbent tube for sampling vapour all housed in a single unit. Filter and sorbent are analysed
by infra red (IR) spectroscopy. This sampling device has been regularly used by the BIA for
measuring total airborne oil for comparison with a German MAK exposure limit of 10 mg/m³,
but is uncommon in the UK. It is said to be capable of measuring 0.5 to 500 mg/m³, sampling
at 3.5 litres/min over a 2 hour period, but recent developments to the hardware altering flow
rate requirements should allow it to sample for longer periods at lower flow rates.
The Ford Motor company have at one time used 37 mm glass fibre filters, (presumably held
in ‘total dust’ closed face filter cassettes), and 8 mm charcoal tube to sample oil mist and
vapour at 1 litre/min. The filters were analysed gravimetrically by solvent desorption with
2
trichloroethylene or perchloroethylene, the sorbent by solvent desorption with carbon
disulphide and analysis by gas chromatography (GC). The sampler would not have collected
the inhalable fraction required for comparison with UK limit values, and it is uncertain
whether the procedure took precautions to minimise filter sample losses during storage and
equilibration.
An alternative to the GGP sampler using more familiar and more common inhalable filter
samplers (such as the Institute of Occupational Medicine (IOM) sampler or the multi-orifice
sampler (MOS)) would be to combine them in series with commercially available sorbent
tubes. Such combinations need to be tested to see quite what restrictions the problems
mentioned will have on application and performance. One way to overcome these problems
would be to reduce the flow rate through a sorbent tube whilst maintaining the required high
flow rate through the filter sampler by splitting the air flow, so that only a portion of the air
sampled through the filter also goes through the sorbent tube. Another strategy would be to
use a diffusive sampler behind the filter sampler to sample the vapour. A diffusive sampler
should present no problems associated with pumped sorbent tubes, but will have problems of
its own, namely sensitivity and knowledge of the uptake rates of the analytes involved. An
alternative to combining filter and vapour samplers may be to sample both using just a
pumped sorbent tube, however such a method would not necessarily sample the inhalable
fraction of the mist usually required for comparison with limit values.
If the vapour concentration could be accurately determined, it should be possible to calculate
a mist concentration from the total oil concentration. Pumped sampling methods will sample
some mist, however diffusive sampling methods may be unaffected by the presence of mist
particles and offer a way of measuring the vapour only concentration.
Analytical methods for oil mist on filters are well established, but as yet no work has been
done on the effect of potential evaporative losses from filters of light mineral oil mist samples
during storage. The mist (and vapour) from these types of oils will differ in composition from
the bulk oil and this may have implications on calibration of IR spectroscopic methods. Apart
from IR spectroscopy, GC appears to be the only widely applicable alternative method for
measuring the vapour, however sensitivity and choice of calibration material may cause
problems.
Once estasblished, suitable sampling and analytical methods for measuring exposure to
volatile mineral oil based MWF are to be evaluated by initially sampling artificial aerosols of
a commercial MWF in the laboratory, and then by use in the field.
2. EQUIPMENT
2.1. Samplers
Most of the sampling devices tested were combinations of filter samplers to trap the mist
connected in series with some type of vapour trap behind. The filter samplers used were ones
which collect the inhalable fraction of the aerosol, ensuring that the samples collected will be
comparable with exposure limit values. Such samplers are described in MDHS 14
(HSE 1997a), and include the IOM, MOS and CIS samplers. Table 1 illustrates some of the
samplers characteristics.
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