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This article assumes you know the basics: what an occupational exposure limit is, the difference between 8-hour TWA, STEL, ceiling and biological limit values, and which bodies publish them. If not, start with Occupational Exposure Limits: TWA, STEL & Ceiling Values Explained. This article then answers the question: which limit value takes precedence when several are available?
Key Summary: DOHSBase uses a unique 6-level hierarchy to rank occupational exposure limit values by reliability and regulatory authority. Level 1: legal limit values of the user’s own country (binding). Level 2: health-based values from independent scientific committees without stakeholder influence (e.g. DECOS). Level 3: health-based values with possible stakeholder influence (e.g. ACGIH TLVs). Level 4: values calculated with standard factors, including REACH DNELs (5,300+ substances). Level 5: hazard banding-based values, including DOHSBase kick-off values (100,000+ substances). Level 6: single-endpoint and judgment-based values (nano reference values). The hierarchy is jurisdiction-aware, showing different primary values per country.
One of the key features of DOHSBase is the overview of occupational exposure limit values. For clarity, not all existing limit values are displayed. Only the limit values we consider most relevant are presented. The order in which the most appropriate are displayed is based on the DOHSBase hierarchy.
The DOHSBase hierarchy for ranking limit values has six levels. Legal compliance limits are always displayed first. It is important to realize that a customer in Spain will see different limit values and in a different order than a customer in France: since harmonization between countries does not exist, the legal limit values of your own country will appear preferentially and with a higher rank.
In the absence of a legal limit value, DOHSBase presents health-based limit values. These limit values are derived by independent scientific bodies, based solely on health effects with a scientific weighing of all dose-response information.
Why the Hierarchy Matters
For any given substance, multiple limit values may exist – a national legal limit, one or more health-based recommendations from scientific committees, a REACH DNEL, and possibly a kick-off value. Without a clear framework for ranking these values, occupational hygienists would need to evaluate each source individually and make a judgment call about which value to apply. The DOHSBase hierarchy eliminates this ambiguity by providing a consistent, transparent ranking that reflects both regulatory authority and scientific rigor.
The hierarchy also has direct implications for compliance. An employer who applies the highest-ranked available limit value can demonstrate that they have followed a structured, defensible approach to determining the applicable exposure benchmark. This is particularly important during regulatory inspections, where the rationale for choosing a specific limit value may be scrutinized.
The Six Hierarchy Levels
Level 1: Legal Limit Value of Your Own Country
The highest-ranked limit value is always the legally binding OEL in the user’s own country. These are limit values that have been formally adopted into national legislation and carry the force of law. Employers are legally required to ensure that workplace exposures do not exceed these values.
Examples include the Dutch Grenswaarden published by the Ministry of Social Affairs and Employment, the French Valeurs Limites d’Exposition Professionnelle (VLEPs) published by the Ministry of Labour, and the German Arbeitsplatzgrenzwerte (AGW) established by the Committee on Hazardous Substances (AGS).
Legal limit values take precedence in the DOHSBase hierarchy because compliance with them is not optional. If a legal limit exists for a substance in your jurisdiction, it is the value you must use.
Level 2: Health-Based Limit Values Without Stakeholder Influence
When no legal limit exists in the user’s country, DOHSBase next presents health-based limit values derived by independent scientific committees operating without direct stakeholder influence. These committees base their recommendations solely on toxicological and epidemiological evidence, applying scientific criteria to establish a concentration below which adverse health effects are not expected.
A key example is the work of the Dutch Expert Committee on Occupational Safety (DECOS) of the Health Council of the Netherlands. DECOS recommendations are purely health-based and do not take socioeconomic feasibility into account. Similarly, the former EU Scientific Committee on Occupational Exposure Limits (SCOEL) produced health-based recommendations at the European level.
These values rank second because they represent the best available scientific assessment of a safe exposure level, free from political or economic compromise.
Level 3: Health-Based Limit Values with Possible Stakeholder Influence
The third level includes limit values that are health-based but may have been subject to input from stakeholders during the derivation process. This category includes values from bodies where industry representatives, employer organizations, or trade unions participate in the limit-setting process.
An example is the occupational exposure limits recommended by the American Conference of Governmental Industrial Hygienists (ACGIH), known as Threshold Limit Values (TLVs). While TLVs are developed by expert committees and grounded in health data, the ACGIH process may incorporate practical feasibility considerations. Other examples include values from national tripartite committees where social partners have a formal role.
These values remain scientifically robust but are ranked one level lower because the potential for non-health factors to influence the final number cannot be entirely excluded.
Level 4: Limit Values Calculated with Standard Factors (Including DNELs)
The fourth level encompasses values derived using standardized calculation methods rather than comprehensive toxicological review. The most prominent examples are REACH DNELs (Derived No-Effect Levels), which are calculated by applying default assessment factors to available toxicity data from registration dossiers.
DOHSBase includes over 5,300 REACH DNELs. While these values are substance-specific and based on actual toxicity data, their reliability depends heavily on the quality and completeness of the underlying registration dossier. The use of default assessment factors, rather than expert judgment of the full weight of evidence, places them below health-based values in the hierarchy.
Level 5: Limit Values Based on Hazard Banding Systems (Including Kick-Off Values)
The fifth level includes values derived from hazard banding approaches, where substances are grouped by their hazard classification and assigned exposure benchmarks based on the statistical distribution of known OELs within their group. DOHSBase kick-off values are the primary example at this level.
Kick-off values are set at the 10th percentile of the limit value distribution for substances sharing the same most severe H-statement, making them conservative estimates. Over 100,000 kick-off values are available in DOHSBase, covering a vast number of substances that would otherwise have no quantitative exposure benchmark at all.
While kick-off values are not substance-specific in the way that health-based OELs are, they provide a scientifically grounded starting point that has been recognized by the Dutch Labour Inspectorate since 2012.
Level 6: Single Endpoint and Judgment-Based Values
The lowest level in the hierarchy includes values that are based on a single toxicological endpoint or on expert judgment rather than a comprehensive assessment. Currently, DOHSBase includes nano reference values at this level – provisional benchmarks for nanomaterials that are based on limited data and precautionary principles.
These values are included in DOHSBase because they represent the best available guidance for specific substance categories, but their limited data basis warrants the lowest hierarchical ranking.
How Different Countries See Different Results
Because occupational exposure limits are set at the national level and harmonization between countries remains limited, the same substance can display different primary limit values depending on which DOHSBase database you consult. A user in the Netherlands will see Dutch legal limit values at Level 1, while a user in France will see French VLEPs. If neither country has a legal limit for a particular substance, both users may see the same health-based or kick-off value, but the pathway through the hierarchy to reach that value will differ.
This jurisdiction-aware approach is one of the distinguishing features of DOHSBase. Rather than presenting a single “global” limit value that may not reflect local regulatory requirements, DOHSBase shows you the value that is most relevant to your specific compliance context.
Why Values Move, and Why the Strictest Is Not Automatically Right
Exposure limits do not stand still. Some move because the toxicology advances: new studies, a re-evaluation by RAC or the Gezondheidsraad, or a revised classification. Others move because legislation is slow. A European indicative limit applies only once it is transposed into national law, and transposition runs at different speeds in each member state. The result is that the same substance can carry different values in different countries at the same moment without either being wrong: they sit at different stages of the same process. Anyone documenting an assessment should therefore record not only the value but its source, its level in the hierarchy, and its date.
From this a rule of thumb is sometimes drawn: simply apply the strictest value published anywhere. It is not a good rule, for two reasons. Legally, a stricter foreign value does not discharge you from the national statutory limit, which remains the figure the labour inspectorate tests against even where an advisory body elsewhere sits lower. Substantively, the rule ignores why a value is lower. A lower value may rest on newer and better evidence, but equally on a precautionary approach to sparse data, or on a different assumption about exposure duration. The hierarchy therefore ranks on authority and the strength of the underlying assessment, not on the size of the number. The strictest value is a signal worth examining, not an answer in itself.
Frequently asked questions
Which exposure limit takes precedence when several exist?
The highest available rank in the hierarchy above. For a Dutch workplace that is the statutory value from annex XIII; where none exists you step down level by level. Where several values sit at the same level, take the most recent and record which one you used.
Are SER limit values a separate standard?
No. The SER advises on public limit values and its advice precedes statutory adoption, so it counts as a health-based recommendation until it is taken up in annex XIII, at which point it becomes the statutory value.
Can a foreign limit be used where the Netherlands has none?
Yes as a comparison and as supporting evidence, but not as a standard. A German or British value does not bind a Dutch employer. Use it to judge whether your controls are in line, and record the regulator and the year alongside it.
Data Richness and the Hierarchy
A limit value in a higher hierarchical position also correlates with increasing data richness and the inclusion of human health data (epidemiology). Legal and health-based OELs at the top of the hierarchy are typically supported by extensive toxicological dossiers, animal studies, and often human epidemiological evidence. Values at lower levels rely on progressively less substance-specific data, from standardized calculation factors (Level 4) to statistical distributions across hazard groups (Level 5).
At all levels, “read-across” can occur, meaning that properties of one substance have been validated for use for other, similar chemicals. This is a common and accepted practice in toxicology and regulatory science, reflecting the reality that closely related substances often share similar toxicological profiles.