Last reviewed 25 May 2017

In this special report Mark Selby of Denehurst Chemical Safety Ltd discusses Exposure Scenarios (ES) and Extended Safety Data Sheets (e-SDS) highlighting the need for effective communication and meaningful user-specific information to enable those writing e-SDSs to understand the incoming ES and what inputs need to be acted upon.


The terms “Exposure Scenario” (ES) and “Extended Safety Data Sheets” are part of the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) terminology that is not always fully understood. As with other regulatory requirements, many see these as something that needs to be done and little thought goes into the usefulness or relevance of the output.

The main result so far is that recipients of the e-SDS need to work through a lot more text that is, to be blunt, not always very useful. Many e-SDS can be very long and although there is a general improvement, it can be difficult to find specific details. The information provided can also look very complex and terms used may not be familiar to most readers. However, the concepts are not difficult to understand and indeed, in theory, there are benefits in terms of providing users with more detailed information to allow them to apply appropriate risk management details.

The problem is that, in practice, most ESs have either been over complicated or fail to provide any useful information. So far, it appears that suppliers are more interested in formatting and “box-ticking” than in actually providing something of value to the recipient.

The key objective is that industry is recommending uses for chemical products that lead to acceptable levels of exposure and the SDS remains the main tool for communication. There is also a move to a “bottom up” approach that gives more practical support for users and the Safe Use of Mixture Information (SUMI) project is trying to make the information more concise and useful.

What the legal text says

Where a Chemical Safety Report (CSR) is prepared as part of registration, the findings arising from scenarios for exposure and estimates of exposure that result from the proposed uses need to be communicated to downstream users as part of the SDS. The SDS is therefore “extended” to include the ES. The SDS can be presented with a summary of the CSR findings, as it is accepted that the complex details in a full CSR are inappropriate.

A CSR is required for substances registered at levels above 10t and every registrant will need to either present their own personalised CSR with their IUCLID dossier, or sign into (and agree with) a joint CSR prepared as part of joint submissions.

There are also issues around minor uses of less than 1t where the ES may not be available as low volume uses do not need to be considered in the CSR.

Only hazardous substances need an SDS and ES and for many non-hazardous materials where the suppliers provide SDS for “information”, there will be no ES.

For onward supply of mixtures (including diluted substances), the onward supplier needs to issue a new SDS (if the mixture is hazardous), or, if non-hazardous, supply an SDS on demand if it contains hazardous components above “levels of concern”. For any ingredient listed in the SDS Section 3, the details within ESs for those substances need to be communicated onwards as considered relevant for the use of the mixture. The legal text does not specify whether this is as a new mixture ES, as a collection of substance ES or simply including the findings in the body of the mixture SDS.

The concept of the SUMI is to distill relevant details from the ES of contributing substances into a simple, short, document that is specific for a use. The SUMI carries no legal basis and is intended only to clarify the onward communication of details from component substance ES.

Acting on the ES

There is no obligation to obey ES and the extended SDS does not replace existing workplace, environmental and consumer legislation. One concern of the SUMI is that it is starting to look like a workplace safety assessment (eg UK Control of Substances Hazardous to Health) and some recipients may think of it as a replacement to their own assessments; irrespective of the content of the ES or SUMI, the recipient must legally make their own worker safety assessment.

The objective of the additional information is to provide more information to allow the user of chemicals to enhance their existing safety assessments. In many cases, it is likely that the recipient will not have to change existing working practice, but there will also be times that the recipient will decide that they need to tighten risk management to reduce exposure; conversely, there may also be occasions that controls have been too strict and the new information allows some relaxing of historical practices.

The important point to understand is that the recipient has an obligation to be satisfied by the recommendations for risk management and must have confidence that the supplier has got it right. If there is reason to believe that the incoming SDS, ES or SUMI is incorrect, the recipient should question their supplier. Employers and onward suppliers retain full legal responsibility for the safety of their workers and customers; this has not changed.

It is therefore essential for recipients to read and fully understand the SDS and ES and if there are any parts that are not fully understood or that do not look right, the supplier needs to be contacted and asked for help.

Uses not covered?

If the use is not covered by the supplier’s registration and ES (ie the substance is hazardous and a chemical safety assessment has not taken place for that use), the recipient can either ask the supplier to take this into account, or prepare their own assessment and then report the use to the European Chemicals Agency (ECHA). If the supplier has to change their CSR, then a spontaneous update to their registration is needed (which will not carry a fee).

However, the first point of action is to check that the use is definitely not covered as generic uses may have been described that do not specifically mention your use but which do cover the use in practice; an example may be “industrial spraying and surface treatment” that will cover painting, application of corrosion inhibition, surface cleaning, etc but may not mention specific industries.

The need to consider the uses of the registrant and the need to inform ECHA are covered in Article 38 of REACH. If the use is for less than 1t, then the supplier does not have to consider the use and the user need not prepare a formal assessment or notify ECHA, Article 39.

If having to notify ECHA of a use, the information to be supplied is limited to substance identity, sites and use descriptions and is submitted within REACH IT. There are no fees levied for this activity. Notification of ECHA needs to be within six months of receiving an extended SDS that does not cover the specific uses (unless it is non-hazardous or has been diluted to concentrations no longer considered hazardous).

A downstream CSR where the user makes their own estimates for exposure and can confirm exposure is within safe levels needs to be prepared within 12 months of receiving an SDS without the intended use, but does not need to be supplied to ECHA. This needs to be kept on file and may be subject to review by national agencies as part of a workplace or consumer protection inspection. Although sounding onerous, recipients should be conducting this sort of assessment anyway to confirm products are safe for use.

If uses are covered, but it is not possible, or appropriate, to follow recommendations in the ES, then “scaling” can be applied in some circumstances; this is covered in more detail in a later section of this report.

The science — risk characterisation ratio

The ratio between the level of exposure and the amount of exposure causing harm to no effect levels is ultimately used as an indicator of risk. The ratio is the degree of exposure to humans or the environment versus the level estimated to cause no adverse effect.

The scale of the risk can therefore be crudely measured by considering this ratio. A figure of less than one (<1) is required to demonstrate that exposure is less than levels estimated to result in hazardous effects and therefore, the level of risk is “acceptable”.

The actual scientific value of a numerical value for risk may appear inappropriate (with the fundamental question of whether risk can be quantified numerically), but this does allow comparisons to be made between ESs or between different substances. However, it must be remembered that both parts of the equation (hazard and exposure) are derived using defaults and safety margins and although potentially flawed, this simple ratio does allow the degree of risk to be expressed easily and materials identified as high or low risk.

The SDS remains the key communication tool and is supported by the other documents, if any of the sources of hazard or exposure data or the CSR itself are incomplete, the SDS will possibly fail to provide sufficient information.

Hazard assessment

REACH requires that the hazard data is collated in the form of a Chemical Safety Assessment (CSA). This needs to include hazard data relating to physico-chemical data, human health and environment and conclude with classification and choice of hazard statement to ensure correct labelling. As part of this process, every substance will need a “derived no (or minimal) effect level” (DNEL or DMEL) to be assigned.

It is impossible to isolate hazard from exposure at any stage of the process as high exposure may mean that there is a greater need for a high level of certainty in the data. For low exposure uses, read across or modelling may suffice, but if high exposure, good quality testing may be necessary. Exposure waivers are possible for registration (further guidance is available on this), but they only apply if the registered uses indeed result in no exposure by these routes.

The Derived No (Minimal) Effect Level or DN(M)EL

The DNEL is calculated by taking the toxicity end points, including acute, sub-acute or chronic toxicity and applying “safety factors” depending on the species tested, the duration of the study, the dose route, etc. The methods to make this calculation and the science that went into the process are too complex to discuss in this report, but it is described in Chapter R-8 of the technical guidance.

The DNEL or DMEL is reported in the summary of toxicity in IUCLID (found in disseminated dossiers) and also reported in Section 8 of the SDS. Many dossiers already submitted have poorly thought through DNELs or gaps with suggestions that they are not needed. As ECHA slowly reviews the dossiers, the quality of the figures should improve and indeed, many registrants are making spontaneous updates to dossiers. Once a substance is registered and the dossier published, the DNEL is effectively fixed until the dossier is updated. But note, these do change and the suppliers must past on “without delay” changes to such information through revising SDS.

Those supplying hazardous substances (on their own, or in mixtures and above thresholds of concern) are expected to report the figures in the SDS. The problem is that many readers of the SDS will not understand the DNEL and may confuse this with the exposure limits (eg workplace exposure limit (WEL)). Unfortunately, there is likely to be considerable confusion as a result of publishing these numbers and WEL still remain the limits in the appropriate countries under remaining national legislation.

Further guidance is available on DNEL estimates, but it is best left to experts who can use more than simple tables in the guidance to determine what are effectively the “safe” levels for exposure. As a recipient of DNELs or DMELs in an SDS, first perform a sanity check. Some very high figures have been published in the disseminated dossiers.

Predicted No Effect Concentration (PNEC)

The environmental equivalent of the DNEL is the PNEC — this is a more simple process as there are standard safety factors applied according to the type of tests performed, such as toxicity to fish, Daphnia or algae. For acute studies, a safety factor of 1000 is applied to the EC50 value; ie a Daphnia EC50 following 48 hours exposure of 50mg/litre would lead to a PNEC of 0.05mg/litre. Longer term studies require a smaller safety factor, as indicated below and if there are multiple studies, for example more than one algal study, the results can be refined further.

If there is no effect at the limit of solubility, this limit needs to be used as a starting point.


Although guidance for preparing the CSR and in particular, ES, is extremely complex, for most substances that are of low hazard, only generic descriptions and scenarios are necessary.

For formulators, selling on mixtures containing the hazardous substances, there is a need to both understand the ES so that they can apply the risk management measures (RMM) for their own activities, and then pass on relevant parts of the ES when supplying mixtures to their own customers.

To prepare an ES it is, therefore, essential to know how the substance and any subsequent mixtures are used. The best people to do this are those involved in practical health and safety or process engineering and not regulatory departments or external consultants.

To help industry, ECHA has provided a coding system (Chapter R-12 of the technical guidance) and the PROC, PC and ERC codes for processes, product categories and environmental release are now fairly well known. However, note that these codes are not indicated in any legal text and should not be seen as a hindrance for those writing ES. They are there to help and to allow certain activities to be categorised to be put into models such as Chesar (free exposure modelling software used for REACH Registration).

For example, PROC 5 covers blending and this will carry certain default levels of exposure to workers. PROC 8 covers packaging and transfer of chemicals and sub-categories a and b relate to closed or open activities — closed being completely confined and automated and open describing typical pouring or pumping with non-dedicated equipment. Guidance is good in Chapter R-12 with further advice in Chapters R-14, -15 and -16.

Many uses are difficult to ascribe to a specific code so for the writer or reader of the ES, it is sometimes necessary to avoid being too constrained by what is a merely an indicator of exposure types or product types.

The potential exposure to consumers needs to be described. If only supplied as a substance or preparation for industrial use with no onward supply in products to the consumer, this must be stated. The statement that supply is “limited for professional use” is a good risk management measure; obviously if the customer wants to supply to the general public, then the risk assessment will need to be revised to take this into account. This could be done by either the registrant or the customer; the key point is that everyone in the supply chain is satisfied that they can supply onwards within the scope of the registration and risk assessment.

Exposure to the environment

The Predicted Environmental Concentration (PEC) is the end-point of the environmental exposure assessment and can be calculated using data for the degradation or distribution of the substance in the environment (between water, air and solids) using physico-chemical and biodegradation data. As well as the test data, other key factors include how the substance is manufactured, formulated or used and the dilution factors from use.

Default figures are provided in the technical guidance documents, describing estimated concentrations of waste in effluent, standard dilution factors, sizes of water treatment plants, etc. These default values consider worse-case scenarios with, for example, 2% of material produced being lost to waste water, the position of the production unit in a small town with a small waste treatment works, and with final discharge going into a small river. However, where only limited sites are involved in production, formulation or use, location-specific factors can be used, such as the size of the waste treatment works, river flow rates, etc. Additionally, users at specific sites with large treatment plants and greater dilution may find it is possible to apply scaling factors.

Scaling factors — health

Scaling is a term that simply reflects how figures in an ES can be manipulated to allow for use at higher or lower levels than described by ESs. For example, exposure to 2mg/m3 of dust for 4 hours will result in the same level of total exposure as 8mg/m3 over 1 hour. This works, as long as 8mg/m3 is not irritating at that higher level. Knowing whether effects are local, systemic, acute or chronic are essential and a good ES will provide scaling advice.

The same applied to dilution; a substance that biodegrades can have an acceptable level of loss to waste water that results in a PEC of less than PNEC. It may be acceptable to increase the number of kilos lost to waste water if the receiving treatment plant has a higher volume of water; conversely, if a site has a small treatment plant and low dilution factors, the level of loss may need to be reduced accordingly.

The various models used to estimate exposure to the environment or to works rely heavily on “scaling”. This means that by reducing the time a worker is exposed (perhaps limiting to 15 minutes a day for a simple task), the exposure will be less than if doing the same task all day.

Duration factors (taken from ECETOC TRA

Duration of activity

Modifying factor

4–8 hours


1–4 hours


15 minutes–1 hour


<15 minutes


It will be noted that this is not a linear approach. Put very simply, if a worker is only exposed for 15 minutes a day, the level of exposure could be 10 times greater than if in that working environment all day.

The concern is that this is only really applicable for certain types of substance; for something corrosive such as a strong acid, clearly 15 minutes at a 10 times higher level may be damaging; a one-minute exposure to a corrosive substance will often be enough to cause damage.

Likewise, chemicals that are acutely toxic, but less toxic over a longer period, such as caffeine, will not scale well; imagine a day’s worth of coffee in a 15-minute binge. Chemicals that accumulate will again not “scale” well since it is the total dose that counts and not the concentration.

Scaling can also apply to changing the level of worker protection; for example, expensive local extraction and ventilation systems (eg LEV) can reduce worker exposure significantly and such engineering measures must take precedence over Personal Protection Equipment. However, for the odd one-off activity, Respiratory Protection can be substituted; again, such measures must only be considered following advice from workplace safety specialists and they will need details on the chemical properties and toxicity to make this decision.

Having considered the exceptions, there are many substances that can be scaled successfully and the models may suggest a risk management measure to reduce daily exposure. However, before considering whether this can be applied, the toxicological mechanisms and potential metabolism must be understood; a well-written ES will give advice.

Scaling factors — environment

The environmental exposure assessment models rely on far more basic defaults and if there are site-specific conditions to use scaling may be applied for certain types of substance; as with human health effects, only if a chemical has certain properties can scaling actually be applied.

The key defaults to consider are:

  • size of sewage treatment plant (STP), 2000m3/day (serving 10,000 people)

  • dilution into (small river) × 10 (receiving water flow 18,000m3/day)

  • dilution into sea × 100.

So, if on a large river or in a big city, there will be more dilution, ensuring that PEC is less than PNEC giving a Risk Characterisation Ration <1.

But, this only applies for water-soluble biodegradable materials that do not accumulate in sediments or bioconcentrate in aquatic or marine organisms. Therefore, care is needed if wanting to apply this.

Another area of confusion is the number of days per year of use; typically, increasing the number of days of use implies more exposure, but in this case, more days means more dilution. So, if an ES suggests 100t per annum over 300 days, it is a minimum of 300 days. A better way to consider this is quantity per day and if expressed as 333kg/day, it is a lot clearer to the reader.

Exposure scenario templates

There is no fixed template, but there is a move towards a more recognisable “4 section” template. It is possible that the formatting will become more standardised in the future and this will be in part pushed by software systems.

As well as proprietary software that uses phrase libraries to allow automated translations (ES are part of the SDS and subject to the same requirements for translation), the Chesar software that is used as part of the CSR exposure assessment provides an output in Rich Text Format that allows formatting into the SDS.

Chesar is software provided by ECHA that can be downloaded for free and is typically used by those generating the CSR. Although Chesar is itself a simple tool to use and links well to IUCLID (REACH dossier authoring software), it can over-simplify complex scenarios of use. Likewise, in the hands of an eager user (especially if being paid by the hour), it is possible to generate multiple contributing scenarios for every use imaginable, making the ES very long and repetitive.

Ultimately, the template is therefore less important than the content and if necessary, writers need to adapt their template to suit their customer’s likely needs. The message is for recipients to expect and to tolerate different templates; however, if the ES is irrelevant, confusing or apparently incorrect, it is important that the supplier is contacted and clarification sought.


It is impossible to separate the processes of reading and writing ES; those writing e-SDS need to understand the incoming ES and understand what inputs are relevant and need to be acted upon. Understanding workplace and environmental exposure is key and the best people to write the ES are those actually in the factory or point of use. Leaving it to regulatory departments or consultants who have not visited the factory will not always result in a practical ES.

A good ES will describe uses in a way that the user can relate to and then provide practical advice, with a view to the skill level of the user, to reduce exposure to levels lower than levels that are estimated to cause an effect to workers, consumers or the environment. This level of “safety” is described as the risk characterisation ratio.

If selling a chemical product for any use, it is essential that the use it is promoted for does not lead to a level of exposure higher than the no-effect levels and if exposure is likely to be too great, risk management measures need to be communicated.

The SDS is the essential communication tool to meet these objectives and workplace safety assessments remain a legally defining requirement for management responsibility.

Limitation of use as a result of receiving this ES

The following points set limits that an on-site health and safety assessor could use to determine safe working practices and environmental control.

  • Handling and blending in “open” systems is acceptable (closed would imply strictly controlled conditions with sealed vessels and transfer pipes/pumping systems).

  • End product has maximum 25% actives.

  • Maximum daily use on site 1000kg.

  • Maximum 100 days handling/potential discharge per annum.

  • Any contact time with the chemical limited to four hours per day (eg Pouring, sampling, connecting control lines, etc).

  • Can be handled indoors, but ventilation must be good with one air exchange per hour.

  • LEV used at 90% effectiveness at points of system opening and failure means breathing equipment [filters defined] to be used that can also offer 90% reduction in exposure.

  • Maximum exposure to workers must be 1.7mg/m3 in the atmosphere and 0.17mg/kg/day dermally.

  • Maximum process temperature 40°C and storage at 30°C.

  • Goggles, suitable gloves [should be defined if possible] should be worn, offering 90% reduction in exposure.

  • Maximum 20kg discharge in waste water per day, if three-hour biological pre-treatment is in place, assuming local treatment plant handles more than 2000m3 water per day and local discharge point into a river is >10 time dilution.

If any of these conditions are not met, re-calculations are needed (scaling). For example, if only 100kg/day used, the waste water pre-treatment may not be necessary if the concentration is re-calculated to be lower that concentrations causing concern. If workers are only handling the chemical for one hour maximum per shift, or at less than 40°C, less effective LEV may be suitable.

These local decisions need to be made by the local management at the point of use; the supplier cannot be expected to know every last detail of the user’s factory.

List of Abbreviations

  • ADI: Acceptable Daily Intake

  • ADR: Transport labelling regulations

  • AF/AS: Assessment Factor / Allometric Scaling (used in estimation of DNEL)

  • ATE: Acute toxicity estimate

  • (GHS)

  • BCF: Bioconcentration Factor

  • CLP: Classification, packaging and labelling Regulation

  • CMR: Carcinogen, Mutagen, Reproductive toxin

  • CSA: Chemical Safety Assessment

  • CSR: Chemical Safety Report

  • DNEL: Derived No Effect Level

  • DMEL: Derived Minimal Effect Level

  • DU: Downstream User

  • EUSES: European Union System for Evaluation of Substances (risk assessment model)

  • ECB: European Chemical Bureau

  • ES: Exposure Scenario

  • ESIS: European Substances Information System (data base of substances in Europe)

  • GHS: Global Harmonised System (classification and labelling)

  • GLP: Good Laboratory Practice (testing quality assurance)

  • HPV: High production volume chemicals

  • IUCLID: Software for data input

  • KIFS: Swedish Chemicals Agency's (KemI's) Code of Statutes

  • Koc: Adsorption Coefficient (water/sediment)

  • Kow: Partition Coefficient, octanol water (also Pow)

  • LD/LC/EC/IC50, etc: Lethal Dose/Lethal Concentration/Effect Concentration/Inhibition Concentration, etc

  • LOAEL: Lowest Observed Adverse Effect Level

  • MEL: Maximum Exposure Limit

  • MoS: Margin of Safety

  • NIOSH: US National Institute for Occupational Safety and Health

  • NOEC: No Observed Effects Concentration

  • NO(A)EL :No Observed (Adverse) Effect Level

  • OES: Occupational Exposure Standard

  • PBT: Persistent, Bioaccumulative, Toxic (environment)

  • PEC: Predicted Environmental Concentration

  • PIC: Prior Informed Consent — supply of hazardous materials to regions with lower controls

  • PNEC: Predicted No Effect Concentration (environment)

  • pKa: Dissociation constant

  • Pow: Partition Coefficient, octanol/water (also Kow)

  • (Q)SAR: (Quantitative) Structure Activity Relationship (modelling based on chemical structure)

  • RMM: Risk Management Measures

  • STOT: Specific Target Organ Toxicity (bits of body affected by over exposure, eg liver)

  • STP: Sewage treatment plant (see WWTP)

  • TDI: Tolerable Daily Intake

  • vPvB: Very Persistent, very Bioaccumulative

  • WEL: Workplace Exposure Limit

  • WGK: Wassergefahrdungklasse — German water quality classification

  • WWTP: Waste Water Treatment Plant