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Controlling health risksfrom rosin (colophony)

based solder fluxes

IntroductionSerious health problems may arise from inhalation offume from rosin (sometimes called 'colophony') or itsderivatives (see page 6) contained in solder fluxes. Thisbooklet is concerned only with risks from rosin and itsderivatives in solder flux, and not other risks which mayarise during soldering. It is aimed at managers ofbusinesses using these fluxes; suppliers of fluxes; andthose who supply, use and maintain fume controlequipment for soldering work. A separate leaflet, Solderfume and you, explains the potential health risks andprecautions for people using these fluxes (Ref 1).

What are the health risks?The heating, during soldering, of the flux containingrosin (or derivatives) produces fume. This fume is one ofthe most significant causes of occupational asthma inthe UK. Once asthma has developed, even smallexposures to fume can lead to asthma attacks whichmay occur immediately or be delayed for severalhours. When fully developed, the condition isirreversible. The fumes can also act as an irritant to theupper respiratory tract and eyes, and on contact withthe skin these fluxes or their fume can cause dermatitis.

Early symptoms from fume exposure can include:

● watering, prickly eyes

● running or blocked nose

● sore throat

● coughing, wheezing, tight chest and breathlessness.

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Sources of exposure

Manual processes

Rosin-based fluxes may be contained in cored solderwire, or in solder paste applied by syringe or othermeans. Liquid flux can be applied from a bottle or bydipping the component or soldering iron into small jarsor pots.

Manual soldering with a hand-held soldering iron posesthe greatest risk of fume exposure because theoperator's head is likely to be near or actually in thefume rising from the iron or workpiece. Desoldering islikely to become more common due to emphasis onrecycling, and when done with a hand-held iron maypose similar risks. Semi-automated processes may alsogive rise to fume. Without suitable controls, there maybe significant risks from fume inhalation and possiblyskin contact at any of these processes. People nearby,or exposed elsewhere to drifting or accumulating fume,may also be at risk.

The use of manual soldering in electronic and electricalassembly, repair and re-work is well known. Otherprocesses which are less obvious (but still important)sources of fume exposure include the repair oftelecommunications equipment, heating andventilation installations and domestic appliances.Manual soldering is frequently done in training,research and educational establishments and in a widerange of transient operations on site.

Even intermittent work can lead to high, short-termexposures, particularly if carried out in an enclosedspace, or at an awkward angle.

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Automated processes

The assembly of printed circuit boards is often highlyautomated with production lines including wave orreflow soldering. Batch work involving wave or reflowsoldering, repair/re-work, desoldering and reclamationmay also be automated. Smaller stand-alone units maybe found away from production areas, for example intraining, research or educational establishments.

Automated equipment can be well enclosed andextracted, reducing the potential for fume exposure.However, workpieces may still be fuming where theyemerge from machines at take-off or inspection points,and in areas where they are stacked and left to cool.Even where soldering plant is enclosed and ventilated,fume may escape into the workroom from these otherareas. It is often not line operators who are most at riskbut others working where fume may drift or accumulate.

Automatic spraying of liquid or foam fluxes is commonbefore wave or reflow soldering. Skin contact with fluxesshould be prevented. Fumes may be generated at thepre-heat stage as well as during and after wave orreflow soldering.

Solder pastes are usually applied by stencil, screenprinting or syringe dispensing. The main risk initially is fromskin contact, but fume will be generated when the flux isheated, as it would with other solder flux applications.

Other areas of potential fume exposure include:automated dipping in solder pots; hot air re-workstations; use of hot plates; at carousels; and duringdesoldering and reclamation work. Batch reflow andcuring ovens not integrated with other automatedprocesses should also be considered.

De-drossing of solder baths may lead to high fume

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exposures. Maintenance staff removing residues fromsoldering and exhaust ventilation systems may also beat risk.

Legal requirementsThe Control of Substances Hazardous to HealthRegulations (COSHH) require a risk assessment to becarried out where substances hazardous to health areused, and exposure to these substances to beprevented, or adequately controlled (Ref 2). Preventionof exposure should take precedence over adequatecontrol where this is reasonably practicable, and maybe achieved by process modification or substitution.

SubstitutionWhen considering any alternative substance or process,users are advised to consult the manufacturers orsuppliers on conditions and limitations of use.

Users should first consider whether a rosin-based flux isreally necessary. Automated and manual solderingoperations, including repair and re-work may bepossible with rosin-free materials. However, changing tosuch a material may significantly affect quality,tolerances, performance levels, output, operationalrequirements (with the need for new plant andequipment) and re-work costs. There may be nosuitable alternative to a rosin-based flux, though newproducts continue to come on to the market.

A suitable risk assessment will need to be carried out onany potential substitute. Although rosin-free fluxes mayremove the asthma risk, they may still present otherhealth and safety risks for which adequate controls,including local exhaust ventilation, may be required.

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Check that any fluxes claimed to be 'rosin-free' really donot present similar health risks. Some fluxes containnatural rosin which has been chemically processed ormodified to produce derivatives. There are alsosynthetic fluxes containing resin acid groups similar tothose in natural rosin. Such derivatives and syntheticalternatives are still of concern.

Some rosin-based fluxes are described as 'mildlyactivated', but this does not affect the amount of rosinpresent or the amount which may be released. Theymay still present the same risk of asthma.

Where a rosin-free alternative is not viable there may stillbe scope for significantly reducing the risk throughcareful consideration of the process. For example, itmay be possible to reduce the amount of flux used orthe percentage of rosin in the flux which is necessary todo the job. Use of nitrogen inert atmospheres onautomated lines is well developed and reduces theamount of flux needed. It may therefore lessen the risk,but should not be regarded as an adequate means ofprotection in itself.

Rosin-reduced fluxes

Other fluxes may be rosin-reduced. Typical cored solderwire contains up to 3% rosin but some no-clean solder wirescontain 0.5 -1.5%. A lower rosin content reduces the level ofrosin fume which may be evolved and so is preferable.However, it will still present some health risk, which may besignificant when factors such as the duration andfrequency of soldering are taken into account. Often, thelower the rosin content, the more difficult it is to achieve agood joint. Users of low-rosin solder wires may be temptedto use extra rosin dip fluxes to compensate.

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Alternatives to soldering

Alternatives to soldering exist for electrical andmechanical connections and should be considered,particularly at the design stage of any process.

Mechanical jointing processes such as crimping andwire wrap for electrical connections; fastening usingscrews or bolts, or compression joints for plumbing andother pipe fitting work may be suitable. Mechanicaljointing is not suitable for most electronic assemblyoperations involving surface mount technology.

Conductive adhesives currently have certain nicheapplications, but their potential use is expanding. Atpresent, they are not commonly used in electricalassemblies due to their unproven technical propertiesand cost. Major changes to equipment design may berequired and they tend not to be compatible with tin-lead solder alloys. The adhesives are often based onepoxy resins or cyanoacrylates which may themselvespresent significant health hazards, includingoccupational asthma and dermatitis. Nevertheless, theycould prove suitable in some circumstances.

New technical developments which have the potentialto replace traditional solder processes are being madeall the time. These include the use of ultrasonic, plasma,laser and micro-welding techniques. The list is notexhaustive.

Control measures in manual solderingprocessesThe COSHH assessment should identify appropriatecontrol measures (see also Solder fume and you, Ref 1).In most cases, some controls will be necessary toprotect against inhalation of fume. These will vary

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according to:

● The type of process: How the operators and othersare exposed; the size and shape of workpieces;stages of the process, including tinning the iron; thetype and gauge of solder; residual fuming of thework and the soldering iron tip while at rest; thenumber and spread of joints; continuous, repetitivework or intermittent, one-off jobs etc;

● The level and nature of the fume: Frequency andduration of the work; number of people soldering;temperature of the iron (fume levels can triplebetween 250-400°C); stickiness of fume affectingextraction design, filtration and maintenance;

● Local conditions: Size of room; general ventilation;provision of make-up air; air currents and sources ofinterference such as moving machinery, doors andwindows; size of workbench; working position andaccessibility.

Specialist advice is recommended before designing asystem or purchasing and installing equipment.Remember, various measures may be taken accordingto the risk. Good general ventilation and carefulpositioning of the operator may be adequate for small-scale, infrequent work. Where the COSHH assessmentshows more complex ventilation systems are required,the system design should ensure:

● effective capture of flux fume at source, so that thelevel is as low as is reasonably practicable in thebreathing zone of everyone in the area;

● suitable location and protection from sticky fumeresidues of critical components such as pumps, fansand ductwork, to prevent loss of performance;

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● effective containment and safe disposal of the fumeand, in the case of recirculating systems, effectivefiltration of the recirculated air;

● adequate provision of make-up air;

● ease of use and maintenance;

● assessment of all running and maintenance costs,including electrical consumption, heat loss andreplacement of consumables such as filters.

The extraction systems described below may all beused for fume control during manual soldering, buteach has limitations as well as advantages. (Users andpotential users are strongly recommended to seekwritten assurances from suppliers on the standard ofcontrol which their products can achieve, together withrecommended conditions and limitations of use. All newequipment should be monitored after installation tocheck that control of fume is adequate.):

1 Multi-position or flexible arm extraction consists ofadjustable, self-supporting, flexible ducting or tubingwith articulated joints, at the end of which a suitablecaptor hood is mounted. The proper design andposition of the hood is critical to effective capture of thefume. Arm diameters typically range from 12-150 mmdepending on the air flow required. The ducting mayconnect to a single stand-alone extraction filtrationsystem or to a multi-branch system.

Advantages: The ability to set it to an optimum position;flexibility in installation; ease and frequency ofmaintenance and ability to capture large amounts offume.

Disadvantages: Reliance on correct adjustment to thework by the operator; applications where the arm needs

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to be continually moved over a wide area; restrictingmovement of the operator and the workpiece at theworkstation.

2 Tip extraction, using a narrow bore tube on the ironitself to capture fume at source. The tube (typically4-12 mm diameter) is either clipped to a normal iron orincorporated in a purpose-made iron. Careful attentionshould be given to the design of the tip or nozzle andextraction rates for effective fume capture.

Advantages: Continuous removal of fume from the ironwhile in use or at rest; easy installation; minimalvolume/flow rate of air avoiding significant heat loss.

Disadvantages: Blockage of the narrow bore tubes withsticky residues requiring regular and frequentmaintenance and cleaning; failure to control fume fromcomponents when moved from the work position; lesseffective for widespread fume production or wherethere is rapid movement around the workpiece.

3 Fume extraction cabinets are enclosures with oneopen side or front connected to either a stand-alone ora multi-branch extraction system. They are available ina variety of shapes and sizes depending on the productand required airflow. Small units, if properly designed,can be used to good effect on applications such assolder pots and soldering iron rest positions.

Advantages: Ability to control all fume sources withinthe enclosure; relatively low maintenance needs; noreliance on correct adjustment by operator.

Disadvantages: Lack of flexibility in installations;possibly poor accessibility; significant installation andrunning costs; possible need for local lighting.

4 Exhaust ventilated benches have a flush fitting

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extraction system, either drawing fumes downwardsthrough the bench or to the rear away from theoperator's breathing zone.

Advantages and disadvantages: Similar to those forextraction cabinets. However, without enclosure, thecapture of fume may not be as effective, butaccessibility is improved. May prove suitable forwidespread work on large items.

5 Fume absorber units describe a range of small,boxed, portable, fan/filter, bench-mounted units whichmay be set close to the soldering operations. Althoughrelatively inexpensive, they can have serious drawbacks.

In particular, the coarse carbon filters usually fitted inthese units have been found in tests by HSE to removeonly a small proportion of the harmful constituents of thefume. Circumstances in which it may be appropriate touse these devices will be very limited (eg very light fume,possibly produced intermittently, and very good generalventilation). Care should be taken to site unit dischargesaway from areas where other people may be affected.

Fume control at other processesAutomated soldering equipment may present seriousrisks if poorly controlled, but it may also significantlyreduce risks by keeping people remote from the fume.Such machines, eg for wave or reflow soldering, usuallyhave purpose-built enclosures to contain fume, withexhaust ports for connection to ducted local extractventilation systems. Sufficient enclosure and exhaustports should be provided to ensure effective capture ofall fume generated. Equipment suppliers shouldrecommend a suitable exhaust flow rate.

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Careful consideration should be given at the designstage to the provision of adequate extract ventilation orother means of fume control at all take-off andinspection points where fume exposure could occur, aswell as at the main soldering stations. Further enclosureand extract ventilation may be required on conveyortransfer lines between plant if workpieces still emit fumethere. Users and suppliers of plant and control systemswill need to assess production operations as a whole,rather than just main soldering stations in isolation.

Adjustable arm extract systems may be useful for hot airre-work, desoldering, solder pots, hot plates andcarousels etc.

Protection of the fume control systemSolder fume forms a sticky residue in pumps, fans andductwork unless these are protected. This residue canrapidly lead to poor extraction, premature pump/fanfailure and duct blockage. Suitable filters should beprovided to protect against performance loss. Solder fumeparticles are typically 0.5 -1.0 micron in diameter, requiringhigh-efficiency filters for effective removal. A plannedmaintenance schedule should be devised andimplemented in consultation with the system manufactureror supplier, to include regular replacement of filters.

Exhaust to atmosphere and recirculating systemsSystems which exhaust to atmosphere should vent to asafe place outside. They may be less costly to buy andeasier to maintain than recirculating systems. However,they may cause significant heat loss.

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Any decision to introduce a recirculating system shouldbe included in the risk assessment. A correctly designedsystem will adequately capture fume and effectivelyremove it before air is recirculated back into theworkplace.

Recirculating systems may reduce the need for lengthyductwork and prevent the need for some buildingalterations. They may also prevent significant heat loss.However, if not adequately designed and protected, orif they fail, the reintroduction of harmful fumes back intothe workplace will put people at risk. Fume filtration iscritical and should be able to remove both particulateand gaseous components. This will involve both high-efficiency particulate filters and suitable chemical filtersfor the gases. Regular replacement of these filters will benecessary and these costs should be taken intoaccount. In particular, the life of the filter for the gaseouscomponent cannot be easily estimated in situ. A carefulestimate of likely life should be made and the filterreplaced at the end of its useful life. A suitable fresh airsupply should be provided, together with adequategeneral ventilation of the work-room, to achieveeffective control.

Other factors and systems of workThe quantity of fume produced is greatly affected by theprocess temperature, rosin levels in fluxes, frequencyand duration of soldering process, solder type, gaugeand total amounts used. These factors in combinationcan have a considerable overall effect and should becarefully assessed as part of the general control strategy.Operational practices should be developed andimplemented to minimise exposure to fume and skincontact. In particular:

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● adequate residence times in ovens or other unitsfitted with extract ventilation should be observedbefore removal of components;

● inspection, maintenance, setting and cleaning staffshould not have access to plant or equipment whichis still emitting fumes, unless they are adequatelyprotected; and

● inspection, maintenance and cleaning needs forplant and control systems such as exhaust ventilationshould be clearly identified and appropriateprocedures drawn up to prevent risk.

Use and maintenance of controlsControls should always be used when required, andregular checks made that they are working effectivelyand are properly adjusted. Suppliers' recommendedmaintenance schedules and procedures should becarefully followed. Maintenance may need to be veryfrequent to prevent loss of performance, for example,tip extraction tubes may need daily cleaning.

Monitoring and failure detection devices for filters andother parts of the system are available and important inmaintaining effective protection. Suitable access andinspection or sampling points should be provided foreffective monitoring and maintenance of the ventilationsystems.

COSHH requires a thorough examination and test of allextraction systems by a competent person at least every14 months. In addition, regular visual inspections shouldbe carried out by a responsible person on site and anydefects promptly rectified. Suitable records should bekept of all such maintenance inspections, tests andexaminations.

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Suitable training and instruction in the use and propermaintenance of control systems should be provided forall operators and other relevant staff.

Personal protective equipment andother precautionsPersonal protective equipment (PPE) should be used forcontrol only as a last resort when prevention or adequatecontrol by other means are not reasonably practicable.For example, respirators may be appropriate for sometransient work such as maintenance or plant cleaning(including de-drossing) where other controls, such aslocal extraction, are not feasible. Operators should notnormally be expected to have to use PPE during routineoperation of a plant or process.

The type of any respirator necessary will be determinedby the COSHH assessment. Respirators with a combinedparticulate and organic vapour filter or cartridge will bethe minimum requirement. Manufacturers or suppliersshould be consulted. Thorough examination and, whereappropriate, test of respirators will be necessary atregular intervals. This should not normally exceed onemonth and may need to be more frequent accordingto type and use. Manufacturers' recommendationsshould be followed. Suitable records should be kept ofall such tests and examinations.

Suitable gloves and other protective clothing may beneeded where there is potential skin contact with rosin-based fluxes or their residues, particularly duringinspection of components or cleaning of equipment,work benches or extraction plant. Any potential forsplashing of liquid fluxes or other solvent materials mayrequire eye protection. All protective clothing, gloves oreye protection used should be properly maintained

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and replaced if necessary.

Adequate washing facilities should be provided, withsuitable sinks; clean, running, hot and cold or warmwater; soap or other cleansing agents; and towels.

Health surveillanceHealth surveillance is a requirement of COSHH where it isappropriate for the protection of the health ofemployees. It is particularly important where there is a riskof occupational asthma, since detection of earlysymptoms can prevent the development of asthma. Anyproblems revealed by health surveillance may alsoindicate failures in control measures or unsuitableworking practices. Extensive guidance on healthsurveillance can be found in Preventing asthma at work:How to control respiratory sensitisers; Medical aspects ofoccupational asthma; and Surveillance of peopleexposed to health risks at work (Refs 3-5).

The need for and type of health surveillance required forthose people exposed to rosin-based solder flux fumewill be determined by the risk assessment. It will requiresupervision by an occupational health practitioner. Formany soldering operations, high-level surveillance willbe appropriate. This should consist of:

● a questionnaire for identifying relevant symptoms,completed six and 12 weeks after starting work involving exposure to rosin-based solder flux fume,and at yearly intervals afterwards;

● measurement of baseline lung function (peak flowand simple spirometry) at the same intervals; and

● arrangements for relevant symptoms to be reportedto a responsible person without delay.

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HSE also recommends a pre-employment assessmentinvolving a respiratory questionnaire and the taking of adetailed work history, together with baseline lungfunction measurements.

A lower level of health surveillance may berecommended by an occupational health practitionerwhere there is good evidence of control (for exampleby sampling and a period of high-level healthsurveillance indicating no problems) or when work isvery intermittent. Some degree of health surveillance willalways be necessary.

A health surveillance programme may also need toinclude skin inspections where the COSHH assessmentshows that risks of dermatitis are significant. Typically,enquiries about skin complaints and inspections ofexposed skin, mainly hands, forearms and face, by aresponsible person at about monthly intervals may beappropriate. Further guidance is available in Healthsurveillance of occupational skin disease (Ref 6).

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References from HSE Books1 Solder fume and you IND(G)248L (single copies free,

ISBN 0 7176 1351 8 for priced packs)

2 COSHH: The new brief guide for employersIND(G)136L (Rev) (single copies free, ISBN 0 7176 11892 for priced packs)

3 Preventing asthma at work: How to control respiratorysensitisers L55 SBN 0 7176 0661 9

4 Medical aspects of occupational asthma MS 25ISBN 0 11 885584 0

5 Surveillance of people exposed to health risks atwork HS(G)61 ISBN 0 7176 0525 6

6 Health surveillance of occupational skin diseaseMS24 ISBN 0 11 885583 2

Further reading from HSE BooksAssessment of exposure to rosin (colophony) basedsolder flux fume Engineering information sheet EIS 17(free)

Resin acids in rosin (colophony) solder flux fumeMDHS 83 ISBN 0 7176 1363 1

Introduction to local exhaust ventilation HS(G)37 ISBN 0 7176 1001 2

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Additional informationThis leaflet is available in priced packs of 10 from HSEBooks, ISBN 0 7176 1383 6. Single free copies are alsoavailable from HSE Books.

HSE priced and free publications are available by mailorder from: HSE Books, P O Box 1999, Sudbury, Suffolk,CO10 6FS (Tel: 01787 881165; Fax: 01787 313995).

HSE priced publications are also available from goodbooksellers.

For other enquiries ring HSE's Infoline, Tel: 0541 545500 orwrite to HSE's Information Centre, Broad Lane, Sheffield,S3 7HQ.

This leaflet contains notes on good practice whichare not compulsory but which you may find helpful inconsidering what you need to do.

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This publication may be freely reproduced, except for advertising,endorsement or commercial purposes. The information it contains iscurrent at 5/97. Please acknowledge the source as HSE.

Printed and published by the Health and Safety ExecutiveIND(G)249L 5/97 C500