Health and SafetyExecutiveMeasurement of oil mist from mineraloil-based metalworking fluidsMDHS84/2Laboratory method using inhalable sampler and gravimetricanalysisScopeMethods for theDetermination ofHazardous SubstancesHealth and SafetyLaboratory1This method describes a gravimetric procedure for the measurement of timeweighted average concentrations of oil mist. Oil mist may be formed from mineraloil used as a coolant or lubricant during the machining of metal components. It isapplicable to aerosol formed by mineral oils with viscosities greater than 18 mm2 s-1(or centi-Stokes, cSt) at 40 C. Lower viscosity oils contain a greater proportion ofvolatile components. The aerosol of a low viscosity oil may be unstable and losevolatile constituents while trapped on a filter during air monitoring, consequently thegravimetric analysis may underestimate the original airborne aerosol concentrationin these samples.Summary2A measured volume of air is drawn through a pre-weighed filter mounted in aninhalable dust sampler. The filter is reweighed to determine the mass of inhalableaerosol deposited on the filter.3If the inhalable particulate concentration is greater than half of any specifiedtarget value, it is recommended that the filter should be further extracted incyclohexane to remove any contribution from any potential interferences depositedon it, by reweighing the filter after extraction.4The use of alternative methods not included in the MDHS series is acceptableprovided they can demonstrate the accuracy and reliability appropriate to theapplication.Recommended sampling5Sampling should be carried out as described in MDHS141 for inhalable dustsfor 2 to 8 hours with a recommended minimum sample volume of 240 litres at 2litres per minute.Prerequisites6Users of this method will need to be familiar with the content of MDHS14.1Safety7Users of this method should be familiar with standard laboratory practice andcarry out a suitable risk assessment. It is the user’s responsibility to establishappropriate health and safety practices and to ensure compliance with regulatoryrequirements.

Health and SafetyExecutiveEquipment8An inhalable dust sampler, pre-cleaned as specified by the manufacturer: AnIOM sampler operated as described in MDHS141 has been found suitable.9Binder-free glass fibre or mixed cellulose ester membrane filters (0.8 μm meanpore diameter). A 25 mm glass fibre GF/A filter has been found to be suitable foruse with the IOM sampler.10Personal sampling pumps that meet the requirements of BS EN 13137.211 A portable flow meter calibrated against a primary standard, with ameasurement uncertainty typically less than 2%.12 Flexible plastic tubing for making a leak-proof connection from the samplingtrain to the pump; belts or harnesses to facilitate attachment of sampling apparatusto subjects; flat-tipped tweezers for loading and unloading the filters into samplercassettes.Laboratory apparatus and reagents13During the analysis, use only reagents of a recognised analytical grade.14Cyclohexane ( 99.5% purity).15 A microbalance calibrated against a primary standard, capable of weighing toa precision of 10 μg or better.16 A selection of laboratory glassware including beakers, measuring cylindersand covered Petri dishes cleaned with acetone and dried.Preparation and sampling17 Load the filters in a clean dust-free environment into clean filter cassettes withthe flat tipped tweezers and allow equilibration with laboratory air overnight beforeweighing. Wear disposable gloves to assemble the filter cassettes to avoidcontamination from the hands.18 Weigh the filter cassettes and place in their transport clips or load into theinhalable dust sampler and cap with the protective covers.19 Set aside a minimum of six pre-weighed filter cassettes to be used as blanks.Where more than forty samples are taken, a minimum of three blank filters shouldbe used for every twenty samples. Ensure that the blanks are treated in the sameway as the samples but without drawing air through them.20 Sampling should be carried out in accordance with the procedures describedin MDHS141 for inhalable dust.21 Select a suitable sampling time, such that the filter does not becomeoverloaded with aerosol (An 8-hour time-weighted average concentration may bederived from the results for two or more consecutive samples).22 Connect each sampler, excluding the blanks, to a sampling pump usingplastic tubing, ensuring that no leaks can occur and set the flow rate using thecalibrated flow meter.Measurement of oil mist from mineral oil-based metalworking fuidsPage 2 of 5

Health and SafetyExecutive23 Attach the sampler in the breathing zone of the subject within 200 mm of themouth and nose.24 When ready to begin sampling, remove the protective cover from the sampler,switch on the pump and check and adjust the flow rate if necessary.25Record the time and sample details at the start of the sampling period.26 At the end of the sampling period, measure the flow rate using the calibratedflow meter, switch off the sampling pump, and record the flow rate and the time.Also note the reading on the elapsed time indicator, if fitted.27 Reseal the sampler with its protective cover and disconnect it from thesampling pump.28 In a clean area, where oil mist is absent, and wearing clean disposable gloves,remove the filter cassette from each sampler, place in their transport clips andtransport back to the laboratory in a suitable container. Alternatively, transport thesamples in the capped sampling heads.29Store the samples in a refrigerator if they are not to be analysed immediately.Sample analysis30 Allow the filters cassettes to equilibrate with laboratory air overnight beforeweighing.Determination of total inhalable particulate concentration31 Weigh the samples and blanks cassettes and calculate the total inhalableparticulate airborne concentration (oil mist and other airborne particles) using theequation:TIP (M2 - M1) – B1 x 1000FxTwhereTIP total inhalable particulate (oil mist and other airborne particles) (mg.m-3)M1 weight of sample cassette before sampling (mg)M2 weight of sample cassette after sampling (mg)B1 average blank filter weight change (mg)F average flow rate during sampling (l.min-1)T sampling time (min)32 Calculate the limit of detection by multiplying the standard deviation of theweight changes in the blank filters by three. Where the blank-corrected weightchange of a sample filter is less than the limit of detection, record the total inhalableparticulate concentration of the sample as less than the limit of detection.Measurement of oil mist from mineral oil-based metalworking fuidsPage 3 of 5

Health and SafetyExecutive33 If the total inhalable particulate airborne concentration exceeds half of anytarget value, the filters should be further analysed by extracting the oil from thefilters and determining the oil mist concentration.Determination of oil mist concentration34 Extract each filter for 1 hour in a covered glass Petri dish in 10 ml ofcyclohexane. Carefully decant the cyclohexane and perform a second extractionwith a further 10 ml of cyclohexane.35 Remove the filter from the petri dish using clean flat-tipped tweezers and allowto dry in a dust-free fume cupboard.36 Reweigh the filters after equilibration overnight and calculate the oil mistconcentration using the equation:OM (M2 - M3) - B2 x 1000FxTwhereOM oil mist concentration (mg.m-3)M2 sample filter weight before solvent extraction (mg)M3 sample filter weight after solvent extraction (mg)B2 average blank filter weight change after extraction (mg)37 Calculate the limit of detection by multiplying the standard deviation of theweight changes in the blank filter by three. Where the blank-corrected weightchange of a sample filter weight changes is less than the limit of detection, recordthe oil mist concentration as less than the limit of detection.Appendix: Additional informationDetection limit1Under the stated sampling and analytical conditions, the limit of detection forsamples taken over an 8-hour sampling period at 2 l.min-1 is typically around0.1 mg.m-3.Overall uncertainty2Preliminary investigations indicate that the analytical method does not exhibitsignificant bias. The analytical recovery from filters spiked with a variety ofmetalworking fluids has been shown to be between 94 and 98%, with a relativestandard deviation of 1%. If the analytical measurements are made within theworking range of the method, the overall uncertainty of the method should meetthe specifications of BS EN 482.3Interferences3As well as collecting oil from the aerosol, there is the possibility of the filteralso collecting oil droplets by impaction from spray formed in the course ofoperations involving the metalworking fluid. In such circumstances the effects mayMeasurement of oil mist from mineral oil-based metalworking fuidsPage 4 of 5

Health and SafetyExecutivebe reduced by choosing an inhalable sampler which minimises the occurrence ofdirect impaction of metalworking fluid droplets by shielding the sample filter to acertain extent. If this interference is perceived to be a potential problem, itsmagnitude can be estimated by collecting two filter samples adjacent to eachother, but with only one connected to a sampling pump. Comparison of theanalytical results from both filters should reveal if there has been significantinterference.4In some workplace atmospheres there may be other aerosols present whichmay contribute to the analytical result (eg water-mix metalworking fluids). Suchinterference will affect this analytical method if they are present at significantconcentration and are soluble in cyclohexane.References1General methods for sampling and gravimetric analysis of respirable, thoracicand inhalable aerosols MDHS14/4 HSE EN 13137:2013 Workplace atmospheres. Pumps for personal sampling ofchemical and biological agents. Requirements and test methods British StandardsInstitution3BS EN 482:2012 Workplace exposure. General requirements for theperformance of procedures for the measurement of chemical agents BritishStandards InstitutionYou should use the current edition of any standards listed.Further informationFor information about health and safety, or to report inconsistencies or inaccuraciesin this guidance, visit You can view HSE guidance online andorder priced publications from the website. HSE priced publications are alsoavailable from bookshops.British Standards can be obtained in PDF or hard copy formats from BSI: or by contacting BSI Customer Services for hard copiesonly Tel: 020 8996 9001 email: [email protected] guidance is issued by the Health and Safety Executive. Following the guidanceis not compulsory, unless specifically stated, and you are free to take other action.But if you do follow the guidance you will normally be doing enough to comply withthe law. Health and safety inspectors seek to secure compliance with the law andmay refer to this guidance.This MDHS is available at: further information about this method or other MDHS methods, please visitHSL’s website: or email: [email protected] Crown copyright If you wish to reuse this information for details. First published 11/14.Published by the Health and Safety ExecutiveMDHS84/211/14Page 5 of 5

change of a sample filter weight changes is less than the limit of detection, record the oil mist concentration as less than the limit of detection. Appendix: Additional information Detection limit 1 Under the stated sampling and analytica