Dangerous substances (chemical and biological)
Chris Keen, Health & Safety Laboratory, UK
- 1 Introduction
- 2 Background
- 3 Relevant legislation
- 4 Basic health risk management
- 5 Summary
- 6 References
- 7 Links for further reading
The article provides a general overview of occupational exposure to dangerous substances. It provides definitions, an introduction to the relevant EU legislation and basic information on how to identify and manage the health risks associated with dangerous substances in the workplace. The article provides an overview for beginners, and signposts the way to additional information.
Many occupations involve the use, or generation, of substances which can be harmful to humans (see the following articles; Irritants, Occupational allergens, Carcinogenic, mutagenic, reprotoxic (CMR) substances, Reproductive effects caused by chemical and biological agents, Endocrine Disrupting Chemicals). Health effects can range from relatively mild, such as eye irritation, to serious diseases such as cancer. Adverse effects can occur as a result of a single episode of high exposure, e.g. high exposure to an irritant substance such as chlorine or nitrogen dioxide may cause an asthma-like condition known as reactive airway dysfunction syndrome (RADS). However, many health effects can arise from lower exposures occurring on a repeated or sustained basis. In considering exposure therefore, it is often necessary to take the exposure level and duration of each period of exposure into account. For substances which can cause some of the most serious health effects, such as cancer and chronic obstructive pulmonary disease (COPD), workers can be exposed to dangerous levels for many years with no obvious illness. By the time symptoms do appear, irreversible harm has already been caused.
Dangerous substances can be gases, liquids or solids. Liquids can be present as mists or vapours and solids as dusts. The physical form of the substance can have a significant impact on the risk to health or safety they present. This is particularly the case with nanomaterials (and nanoparticles) which have particular properties (and present particular hazards) because of their extremely small size.
They can be of chemical or biological nature. Sometimes, it can be obvious that there is the potential for exposure to dangerous substances. However, this is not always the case. Some seemingly innocuous substances, such as flour dust, can cause harm through occupational exposure. Dangerous levels of harmful bacteria can be present in apparently normal, everyday items.
It is clearly of great importance to adequately control worker exposure to these substances. This relies on achieving and sustaining adequate exposure control and requires a degree of competence and expertise. Depending upon the complexity of the situation, the specialist skills of a professional occupational hygienist may be required. With the correct use of exposure controls, work can be performed even with highly toxic substances without risk to the health of workers.
It must be remembered that in addition to health effects, many substances also have other hazards, such as flammability, associated with them. These should be taken into account when designing a risk management strategy. It is important that all health and safety risks associated with dangerous substances are adequately controlled.
Where do dangerous substances occur?
Dangerous substances can occur in a wide range of occupations. These can include:
- Primary extraction such as mining, quarrying, oil and gas drilling. These industries can carry a risk of exposure to minerals (e.g. Respirable crystalline silica), process chemicals (lubricants and drilling muds) and other process generated substances (see below).
- Manufacturing industries, including food production, can carry the risk of exposure to dangerous process chemicals (e.g. isocyanates, solvents), and end products such as paints and lubricants.
- Farming can carry the risk of exposure to pesticides , organics dusts and bioaerosols.
- Service industries - dangerous substances can include cleaning products , asbestos, bioaerosols and process chemicals such as paint strippers and adhesives.
- Healthcare sector workers are potentially exposed to biohazards, pharmaceuticals and disinfectants.
- Construction involves a diverse range of activities, many of which have the potential for exposure to dangerous substances. These include mineral dusts, paints and glues. Refurbishment and demolition activities can present an additional risk of asbestos exposure.
- Recycling – there are a range of hazardous materials, including dusts, toxic metals and biohazards present in the diverse and increasing range of activities that occur in this industry.
This list of industries and exposure risks is not exhaustive. There are risks in many other industries and many other risks, other than those mentioned, can be present in the industries listed. A thorough risk assessment is required to allow any potential for exposure to dangerous substances to be identified, and an effective exposure control strategy to be developed.
How does exposure occur?
The most commonly recognised exposure route is inhalation, i.e. breathing air contaminated with dangerous substances. This is often the most significant route. There are several ways in which dangerous substances can become airborne. Volatile liquids have a natural tendency to generate high levels of vapour, even when handled at room temperature. The application of solvent based paints in poorly ventilated areas can cause drowsiness, dizziness and nausea as the high levels of solvent vapour affect the central nervous system. Any liquid will generate higher levels of vapour if the work process involves heat, with vapour levels increasing as temperature increases. Even low volatility substances can become airborne at high concentrations in aerosol form as a result of spray application or highly energetic processes such as the machining of metal components with liquid coolants.
Solid materials will become airborne if they are in a finely divided (powdered) state. In general, the more finely divided a solid material is, the more dusty it will be and so the more likely it is to become airborne. Mechanical abrasion (drilling, grinding etc.) can generate airborne particulate from bulk solid materials, as can processes involving extreme heat, such as welding and flame cutting.
Dermal (skin) exposure can also lead to harm, either as a result of direct effects on the skin, or chemicals being absorbed through the skin into the body. Dermal exposure most often occurs as a result of direct handling of contaminated items and surfaces, direct immersion of hands (or other parts of the body) into process liquids or by splashing or deposition of aerosol.
Ingestion exposure can occur through hand to mouth transfer or as a result of eating, drinking, smoking or applying cosmetic products or medicines, in contaminated areas. Inadvertent exposure through ingestion or skin contact can also occur through contact with items such as tools (including items such as pens) and PPE (eg gloves and other items of PPE) when removing and handling them.
It is important to remember that the potential for exposure is not limited to process operatives only. Significant exposure can occur for cleaning operatives, especially where dry sweeping methods are used, and for maintenance workers where non-routine activities are often conducted and the exposure controls used during routine production often do not offer any protection.  
Practices which cause the spread of contamination away from production areas, such as the storage of process material in office areas, or taking contaminated workwear home for laundering, can result in harmful exposure occurring to people who have no direct involvement in the work process.
Products which contain dangerous substances should be supplied with sufficient information to allow the user to identify the hazards associated with the material. Within the EU, the information supplied should be in accordance with EC Regulation 1272/2008 (classification, labelling and packaging of substances and mixtures) . The relevant information should be provided on a safety data sheet which is either provided when chemicals are purchased, or made freely available on the internet. The CLP regulations define a list of standardised ‘hazard statements’, along with pictograms which represent the hazard statements, which should be displayed on packaging. Some substances, for example cosmetics, some animal foodstuffs and medicines, may not be supplied with a safety data sheet. This does not mean that they are harmless, and users will need to obtain the relevant information to allow them to conduct a risk assessment, and so use these products safely.
Process- generated contaminants
Many industrial processes generate contaminants which can be hazardous to health. These can be generated through combustion, mechanical abrasion (sanding, grinding, sawing) or other processes which physically or chemically degrade the starting material. Process-generated contaminants can sometimes be difficult to identify, and often a safety data sheet is not available to help with the risk assessment process. They are also not usually covered by REACH (see below).
Common process-generated contaminated substances include:
- Exhaust fume from diesel engines, otherwise known as diesel engine exhaust emissions (DEEE). These contain a complex mixture of gases and particulate material. Many of the individual components have their own specific toxicity, and some have exposure limits assigned to them. DEEE is classified as a human carcinogen by the International Agency for Research on Cancer (IARC).
- Respirable crystalline silica (RCS) is present in the dust from many common minerals. It is a particular issue in the construction industry, where there are many processes which can generate RCS. Tasks which involve the use of power tools to cut or grind cement, brick or stone-based materials can generate very high airborne levels. RCS exposure also occurs in brickmaking, stonemasonry, potteries and quarrying. Uncontrolled exposure to RCS can lead to silicosis, a serious irreversible lung disease. RCS is classified as a carcinogen by IARC.
- Welding fume contains a mixture of toxic gases and particulate material. The composition of the fume is variable, and depends on the type of welding being done and the material being welded. The majority of the fume from metal welding is generated by the consumable (welding rod) rather than the substrate being welded. Information on the composition of the fume should be given on the safety data sheet provided with the consumables. Stainless steel, and other specialist alloys containing high levels of chromium, nickel and manganese carry a particularly high risk. Manual metal arc (stick) welding generates more fume than other techniques, such as MIG and TIG welding. Although welding is most commonly used to join metals, other materials, such as plastics, are also welded and these processes can also generate toxic fume which must be controlled. Fluoropolymers (PTFE and Teflon type materials) in particular carry specific risks.
- Rubber fumes (including the various chemical agents used in the manufacture of rubber products) are a recognised hazard although changes in the composition of the rubbers used in recent years are believed to have reduced the risk of diseases such as bladder cancer.
- Wood dust, generated from sawing, sanding and other woodworking processes, carries a number of health risks. This includes the dust from hard and soft woods, and also composite materials such as medium density fibreboard (MDF) and chipboard, wood chippings used for animal litter or in the paper and pulp industry, or mulch made of wood chippings. Wood dust can cause asthma and is classified by IARC as a carcinogen.
- Biological hazards are present in many situations where organic material is handled. There are risks from animal waste in farming, human tissue and other body fluids in healthcare and discarded food in waste handling and disposal Whenever people are in contact at work with natural or organic materials like soil, clay, plant materials (hay, straw, cotton, etc.), substances of animal origin (wool, hair, etc.) , food, organic dust (e.g. flour, paper dust, animal dander), waste, wastewater, blood and other body fluids, they may be exposed to biological agents. 
- Systems which store and recirculate water have the potential to become contaminated with harmful levels of bacteria. This is especially true where the water can become contaminated with organic material (e.g. metal working fluids) or elevated temperatures are involved (e.g. cooling towers). There are significant risks if the contaminated water becomes airborne as fine droplets. There are many cases where cooling towers contaminated with legionella bacteria have caused significant outbreaks of illness. Such outbreaks can affect the public, as well as workers and often cause multiple fatalities.
The substances discussed above are provided as examples, and there are many other harmful process generated contaminants. Thorough risk assessment is essential in order to identify the potential for exposure to these materials.
Comprehensive European Union (EU) legislation exists governing the management of risks associated with dangerous substances. This is often supported by national legislation in member states. The principal relevant EU legislation as outlined in the listed Directives consists of:
- The Chemical Agents directive (Council directive 98/24/EC) sets out duties for employers related to controlling risks associated with exposure to hazardous substances. These include responsibilities to conduct risk assessments to identify and evaluate the risks from hazardous substance exposure, and responsibilities to implement suitable preventive measurements that offer adequate exposure control.
- European Parliament Directive 2000/54/EC - establishes specific requirements designed to guarantee a better standard of safety and health for workers exposed to biological agents at work.
- The Carcinogens and Mutagens directive (EU directive 2004/37/EC) sets out special requirements for substances which have the potential to cause cancer or genetic mutations in exposed people. The principal requirement is to find a non-carcinogenic/mutagenic alternative. Where this is not possible, a range of robust exposure control requirements are set out in the regulations.
- The Chemical Agents directive introduces the objective of establishing Occupational exposure limits (OELs). These define maximum levels for inhalation exposure to dangerous substances. Indicative and Binding OELs are recommended by the European Commission’s Scientific Committee for Occupational Exposure Limits (SCOEL) and, if accepted, are introduced via additional directives supplementing the provisions of the Chemical Agents directive. Where member states have their own systems for setting and implementing OELs, these have to take into account the OELs set by SCOEL where they exist. However, there are thousands of dangerous substances in common industrial use. OELs are only set for a small proportion of these. It must always be remembered that the absence of an OEL does not imply that there are no health risks associated with a particular substance
- The Registration, Evaluation, Authorisation & restriction of CHemicals (REACH) regulations (EU Regulation No 1907/2006) are mainly aimed at the manufacturers and suppliers of dangerous substances, although end users also have duties under REACH. Under REACH, chemical suppliers are required to define usage scenarios and exposure controls to allow the materials they supply to be used without putting workers’ health at risk. There are particularly stringent requirements for certain types of substance, mainly carcinogens, mutagens and reprotoxins (CMRs) and substances which can have serious environmental effects. Under REACH, these are classed as Substances of Very High Concern (SVHC), and the regulations seek to encourage substitution of such materials with less hazardous alternatives, where possible. The regulations are being implemented in several phases, dependant on the toxicological properties of a particular substance and the quantities being handled within the EU. The regulations will be completely implemented by 2018. Several classes of materials are exempted from REACH, including foodstuffs, natural occurring materials such as minerals, medical products and certain groups of pesticides. The European Chemicals Agency (ECHA) has overall responsibility for the implementation of REACH, working in collaboration with ‘competent authorities’ in individual member states.
- The regulations on classification, labelling and packaging of substances and mixtures (EC regulation 1272/2008)  specify the use of internationally agreed classification criteria and labels to communicate relevant information on chemical health hazards.
Basic health risk management
The risk assessment process is an essential element of effective occupational risk management, and this applies to dangerous substances in the same way as it does to other OSH risks. A risk assessment is nothing more than a careful examination of what, in the workplace, could cause harm to people, so that employers can judge whether more needs to be done to prevent people getting hurt or becoming ill. It is critical that the risk assessment is conducted by a competent person, and for situations involving dangerous substances this may need the skills of an occupational hygienist. The risk assessment process can be summarised by the following steps:
- Identify the hazards. Make an inventory of dangerous substances used in the workplace and those generated by work processes. This should include raw materials, intermediates and end products, and process generated substances.
- Decide who might be exposed, how they might be exposed and to what levels. This should include the workers directly involved with the process, and other workers. Particular attention should be paid to groups of workers who may be at increased risk e.g. young workers, pregnant women and nursing mothers, migrant workers, untrained or inexperienced staff, cleaners, contractors and members of the public who may be exposed as a result of the work activity.
This should not only include handling, but also transport tasks, waste management and storage. Consider combined exposures to substances and combined effects (Fire risks near flammable substances, heavy physical work that can increase the uptake of chemicals, wet work that can increase the effect of chemicals on the skin, working in confined spaces or under particular climatic conditions).
- Assess whether you are using carcinogens or mutagens, for which more stringent rules apply.
- Evaluate the risks and decide on precautions. Exposure control strategies should be based on the principles of good occupational hygiene practice and the hierarchy of control.
- Record your findings and implement them. Make sure it is clear who is responsible, and when and how it has to be done. Make sure workers are properly trained to know how to protect themselves and know whom to report any incidents or health problems The risk assessment should be documented
- Workplaces change and things go wrong. Review your assessment and update if necessary. Monitor the situation regularly, evaluating the effectiveness of prevention measures, investigating any incidents, worker complaints or health problems, and reviewing the risk assessment when there are changes in work procedure, when new chemicals are introduced or when new processes are adopted. When reviewing assessments, any new information should be considered. This may relate to new findings on toxicity, the results of exposure monitoring surveys, or any evidence of ill health in exposed workers. Workers should be involved in the review process to assess any practical issues related to the correct use of the exposure controls provided.
Hierarchy of control
The hierarchy of control defines, in a preferred order, an approach to selecting exposure controls. It takes into account the reliability of various control approaches and also the principles of good occupational hygiene practice. It is defined in article 6.2 of the Chemical Agents Directive.
In summary, the hierarchy of control indicates that total elimination of the hazard is the preferred option, followed by substitution with a less hazardous material. The hierarchy goes on to list various engineering, procedural and PPE based control solutions in order of reliability, the general principle being to achieve control of emissions at source in preference to measures closer to the worker, such as PPE. Numerous, slightly different versions of the hierarchy exist, but all follow the same basic principles. A common element is the inclusion of the STOP principle (Substitute the substance or process, Technical controls, Organisational measures, Personal protective equipment - PPE). In reality, it is unusual that a single control measure will be practical and effective, and a range of controls used in combination usually offers the best solution.
There is a tendency to adopt strategies which rely heavily on PPE when controlling dermal exposure. This is incorrect. The risk management strategy for dermal exposure should follow the same philosophy as that for inhalation exposure. The hierarchy of control applies equally to all exposure routes.
Validation of control – feedback loop
It may be necessary to conduct some form of measurement to ensure that controls being applied are providing adequate exposure control. Most commonly this would be done by estimating or measuring the exposure of workers. Exposure measurement can involve air sampling or biological monitoring. Such monitoring should be repeated or monitored periodically to ensure that controls have been (and continue to be) effective.
Air sampling usually requires personal monitoring on relevant workers. Where air sampling is conducted, it is necessary to have reference methods against which to compare the results. If formal occupational exposure limits exist, these should be used. However, for many substances formal limits do not exist. In these situations, it will be necessary to develop in-house limits to allow exposure monitoring results to be put into context. More complex air sampling techniques, including the use of exposure visualisation, can be useful tools not only in assessing exposure but also in driving exposure reductions.
An assessment strategy for testing compliance with OELs for airborne substances was developed in a joint UK/Netherlands initiative. This was developed to improve the guidance given to employers on how many measurements they should make to allow it to be safely assumed that the chance of exceeding the OEL is acceptably low. A tool has been developed to facilitate its use. The original tool works in Dutch, English, German or French and a Spanish version may also be available. The tool (and the approach embodied in it) has provided the basis for a revised version of EN 689 and this revised draft (prEN 689: 2016) is scheduled for formal vote during 2017. If accepted it will become a national standard in all CEN member countries and, although such standards have no legal standing of their own, they are often regarded as de facto best practice that employers should comply with.
Biological monitoring is most commonly done by urine or blood sampling, although other techniques are available. Some techniques, such as blood sampling, are invasive and this may mean they are not acceptable to some workers. Biological monitoring can offer several advantages over air sampling, including cost, the ability to measure total exposure by all routes, and the ability to assess the efficacy of personal protective equipment. However, biological monitoring methods are not available for such a wide range of substances as for air sampling, and there are medical confidentiality issues to take into account.
The correct choice of a suitable measurement approach, and the competence to interpret and act appropriately on the results, may be beyond the ability of a general OSH practitioner and may require the specialist skills of an occupational hygienist. Exposure monitoring results should always be shared with relevant workers, taking into account confidentiality issues. Biological monitoring results in particular should only be shared on a 1 to 1 basis with the individual participants, unless they consent to sharing these on a wider basis. If results are to be shared more widely, it may be necessary to do this in an anonymous format. However, in the event of such monitoring identifying that an individual has an identifiable disease or adverse health effect which is considered to be the result of exposure at work to the hazardous chemical agent which has prompted the surveillance (or a binding biological limit value for that agent is found to have been exceeded) then, as well as informing the individual, the employer will need to be informed. In such cases, they should be told the minimum necessary to take appropriate actions (including, where appropriate, identifying the individual so that they can be removed from further exposure). Thus it might be sufficient to inform the employer that there have been ‘failed’ tests and that they need to review their risk assessment and control measures.”
Maintenance of exposure controls
Unless an exposure control solution can be found which totally eliminates the risk of exposure to dangerous substances, all controls will require periodic maintenance to ensure that they continue to offer adequate protection.
Engineering controls, such as local exhaust ventilation, require periodic checking to ensure that they continue to work properly. This should incorporate a daily check and a periodic thorough examination and test of the system, which should identify that the controls are operating within their specified parameters and also that they do achieve adequate exposure control. If this test indicates that the controls are not working as they should be, then remedial action should be taken to address this and it may be necessary to implement interim measures, such as the use of respiratory protective equipment, until this can be achieved. Thorough examination and testing should be accompanied by more frequent, less rigorous interim checks and the inclusion of audible or visual alarms which give immediate notice when the performance of LEV systems falls outside specified parameters.
PPE will require maintenance and replacement. Controls which rely on worker behaviour, such as the adoption of certain working practices, also require maintenance in the form of supervision, auditing and refresher training.
In all cases, workers must be properly trained in the correct use of exposure controls. This is essential to allow the controls to achieve and sustain their effectiveness. Periodic refresher training should form part of this strategy.
Dangerous substances occur in many forms in the workplace and uncontrolled exposure can cause serious harm to workers. It is important to achieve, and sustain, adequate exposure control. Managers responsible for occupational safety and health should ensure that individuals have the relevant training and competence to recognise and control dangerous substances. If in doubt, advice should be sought from a competent, professionally qualified occupational hygienist.
- Reactive airways dysfunction syndrome (RADS). Persistent asthma syndrome after high level irritant exposures. S M Brooks; M A Weiss; I L Bernstein. Chest. 1985;88(3):376-384. doi:10.1378/chest.88.3.376
- EU-OSHA – European Agency for Safety and Health at Work, The occupational safety and health of cleaning workers, Literature Review, 2009. Available at: 
- EU-OSHA – European Agency for Safety and Health at Work (28 Dec 2012). E fact 66, Maintenance and hazardous substances. Retrieved on 5 April 2013, from: 
- EU-OSHA – European Agency for Safety and Health at Work, Safe maintenance in practice — Success factors, Summary of an Agency report, Fact sheet 96, 24 Nov 2010. Available at: 
- Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006, OJ L 353. Available at: 
- IARC - International Agency for Research of Cancer, Diesel engine exhaust carcinogenic, Press release N° 213, 12 June 2012. Available at: 
- IARC - International Agency for Research of Cancer, Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 68, Silica, last updated 05/20/97. Available at: 
- IARC - International Agency for Research of Cancer, Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 62, Wood dust and formaldehyde, 1995. Available at: 
- EU-OSHA – European Agency for Safety and Health at Work, Biological agents, Factsheet 41, 2003. Available at: 
- EC - European Commission, Council Directive 98/24/EC of 7 April 1998 on the protection of the health and safety of workers from the risks related to chemical agents at work (fourteenth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC). Available at: 
- Directive 2000/54/EC - biological agents at work of the European Parliament and of the Council of 18 September 2000 on the protection of workers from risks related to exposure to biological agents at work (seventh individual directive within the meaning of Article 16(1) of Directive 89/391/EEC), OJ L 262. Available at: 
- European Commission, Directive 2004/37/EC of the European Parliament and of the Council of 29 April 2004 on the protection of workers from the risks related to exposure to carcinogens or mutagens at work (Sixth individual Directive within the meaning of Article 16(1) of Council Directive 89/391/EEC), OJ L 2004 229/24. Available at: 
- European Commission Directive 2000/39/EC of 8 June 2000 establishing a first list of indicative occupational exposure limit values in implementation of Council Directive 98/24/EC on the protection of the health and safety of workers from the risks related to chemical agents at work, OJ L 2000 38/36. Available at: 
- European Commission Directive 2006/15/EC, Establishing a second list of indicative occupational exposure limit values in implementation of Council Directive 98/24/EC and amending directives 91/322/EEC and 2000/39/EC, OJ L 2006 38/36. Available at: 
- Comission Directive 2009/161/EU of 17 December 2009 establishing a third list of indicative occupational exposure limit values in implementation of Council Directive 98/24/EC and amending Commission Directive 2000/39/EC, OJ L 2009 338/87. Available at: 
- Sithamparanadarajah, R., Controlling skin exposure to chemicals and wet work, 2008.
- European Standard EN689 Workplace atmospheres, Guidance for the assessment by inhalation to chemical agents for comparison with limit values and measurement strategy, 1995. Available at: 
- The Excel tool Implementing the BOHS/NVvA Sampling Strategy. https://www.bsoh.be/?q=en/node/67
- EN 689 Workplace atmospheres. Guidance for the assessment of exposure by inhalation to chemical agents for comparison with limit values and measurement strategy.
- prEN 689 Workplace exposure ― Measurement of exposure by inhalation to chemical agents ― Strategy for testing compliance with occupational exposure limit values.
Links for further reading
Bullock, W.H., Ignacio, J.S., A strategy for assessing and managing occupational exposures, AIHA, 1998.
Cherrie, J., Howie, R., Semple, S., Monitoring for health hazards at work, Wiley-Blackwell, Chichester, 4th edition, 2010.
EU-OSHA – European Agency for Safety and Health at Work (no date). Dangerous Substances. Retrieved on 4 September 2013, from: 
EU-OSHA – European Agency for Safety and Health at Work, Expert forecast on emerging biological risks related to occupational safety and health, 2007. Available at: 
EU-OSHA – European Agency for Safety and Health at Work, Expert forecast on emerging chemical risks related to occupational safety and health, Report, 2009. Available at 
EU-OSHA - European Agency for Safety and Health at Work, Dangerous substances and risk assessment, An European Campaign on Risk Assessment, a PPT presentation, no date. Available at: 
EU-OSHA - European Agency for Safety and Health at Work, Skin diseases and dermal exposure: policy and practice overview, Report, 2008. Available at 
EU-OSHA - European Agency for Safety and Health at Work, Cleaners and dangerous substances,E-fact 41, 2008. Available at: 
EU-OSHA - European Agency for Safety and Health at Work, Preventing harm to cleaning workers, Factsheet 86, 2009. Available at 
EU-OSHA - European Agency for Safety and Health at Work, Preventing harm to cleaning workers, Report, 2009. Available at: 
Gardner, K., Harrington, J.M. (eds), Occupational hygiene, Third edition, 2005. Available at: 
Harrington, J.M., Gill, F.S., Aw, T.C., Gardiner, K., Occupational Health, Brittish Occupational Hygiene Society, 2000.
Perkins, J.L. (ed.), Modern industrial hygiene (Volume 1). Recognition and Evaluation of Chemical Agents, 2nd edition, American Conference of Governmental and Industrial Hygenists, 2008.
Perkins, J.L. (eEd.)., Modern industrial hygiene (Volume 2). Biological aspects, American Conference of Governmental and Industrial Hygenists, 2003.
Perkins, J.L. (eEd.)., Modern industrial hygiene (volume 3). Control of chemical agents. American Conference of Governmental and Industrial Hygenists, 2012.