Key Summary: When a substance has no legal Occupational Exposure Limit, a REACH Derived No-Effect Level (DNEL) can serve as a substance-specific benchmark. To use one correctly: (1) confirm no legal OEL applies, (2) identify the substance by CAS or EC number, (3) look up the substance in the ECHA “Registered Substances” database, (4) select the Worker – Inhalation – Long-term – Systemic DNEL variant out of the 15 possible types, (5) sanity-check the dossier quality and reconcile divergent values between registrants, and (6) compare it against the 8-hour time-weighted average exposure. DNELs are not legally binding, so document the rationale for the value you chose.

A DNEL (Derived No-Effect Level) is the exposure benchmark calculated by chemical registrants under the REACH Regulation. For the occupational hygienist it is a useful fallback: REACH DNELs exist for far more substances than legal OELs do, so when the regulatory limit list runs out, a DNEL often fills the gap. But a DNEL is calculated by the registrant, not vetted by a scientific committee, and a single substance can carry several different DNELs from different registrants. Using one defensibly is a procedure, not a lookup. This guide walks through that procedure. For the conceptual background on how DNELs differ from OELs, see DNEL vs OEL: Understanding the Difference.

Step 1 — Confirm no legal OEL applies first

A DNEL is a fallback, never a substitute for a binding limit. Before reaching for one, check the limit value hierarchy: a legal OEL for your jurisdiction (levels 1–3) always takes precedence and is the value an inspectorate will measure compliance against. Only when no legal OEL, and no health-based committee value, exists for the substance does the DNEL (hierarchy level 4) become the working benchmark. If there is no DNEL either, you fall through to a kick-off value.

Step 2 — Identify the substance unambiguously

Find the CAS number and, where available, the EC number. Substance names and synonyms are unreliable for database lookup; CAS is the key that resolves to a single ECHA registration. For substances registered as a group (common with metals and their compounds), note that the registration may be filed under the parent substance rather than the specific compound you are assessing.

Step 3 — Look up the substance in the ECHA “Registered Substances” database

Go to the ECHA website (echa.europa.eu), open Search for Chemicals, and search the Registered Substances database by CAS number. Open the substance record and navigate to the section Toxicological information → Toxicological information.001. This is where registrants publish the DNELs derived in their Chemical Safety Assessment. ECHA does not announce changes to published DNEL values, so this database is the authoritative current source, not a secondary compilation.

Step 4 — Select the correct DNEL variant

REACH distinguishes up to 15 DNELs per substance, across target group (workers vs. general population), exposure route (inhalation, dermal, oral), duration (long-term vs. acute/short-term), and effect type (systemic vs. local):

For routine workplace airborne exposure, use the Worker – Inhalation – Long-term – Systemic effects DNEL, expressed in mg/m³.
Check whether a Worker – Inhalation – Long-term – Local effects DNEL also exists and is lower; for irritants and sensitisers the local-effect value can be the governing one.
Consider the acute/short-term inhalation DNEL separately if the task involves peak exposures.
If the registrant could derive no safe threshold (typical for non-threshold carcinogens and mutagens), there will be a DMEL (Derived Minimal Effect Level) instead. Treat a DMEL as a risk-based reference, not a no-effect level.

Step 5 — Sanity-check the dossier quality

This is the step that separates correct use from misuse. A DNEL is only as good as the dossier it came from. Where a substance has multiple registrants, you may see materially different DNELs for the same substance and route — this divergence is itself a quality signal. Check the underlying endpoint and the assessment factors the registrant applied: a DNEL built on a sparse dataset with default factors is weaker evidence than one built on a robust study set. When values diverge and you cannot establish which dossier is stronger, choose the more conservative (lower) value and record why. This caution is the entire subject of Careful with that DNEL, Occupational Hygienist! (Scheffers & Wieling, BOHS Exposure Magazine, 2014), recommended reading before relying on a DNEL in a risk assessment.

Step 6 — Apply the DNEL against measured exposure

Compare the selected long-term DNEL against the 8-hour time-weighted average workplace concentration, the same basis you would use for an OEL. If you are testing compliance statistically, the DNEL takes the place of the OEL in the EN 689 / UTL procedure. Because a DNEL is not a legally binding limit, document which DNEL variant you used, which registrant’s value, and the reasoning behind the choice. That record is what makes the assessment defensible if it is later questioned.

The shortcut: DOHSBase pre-resolves this

Steps 3 to 5 are the time-consuming part: locating the registration, extracting the right variant, and reconciling divergent values across registrants. DOHSBase has already done this extraction for 5,300+ worker inhalation DNELs, presented alongside 15,000+ OELs from 30+ countries and ranked in the transparent limit-value hierarchy, with a deep link straight to the ECHA Registered Substances record for verification. Instead of running the lookup per substance, you see the governing benchmark and the DNEL in one view, with the hierarchy already applied.

Common pitfalls

Using a DNEL when a legal OEL exists. The OEL governs; the DNEL is supplementary information at best in that case.
Picking the first DNEL listed. The general-population or dermal value is often listed prominently; the workplace value you need is the worker inhalation long-term one.
Treating a DMEL as a DNEL. A DMEL signals a non-threshold hazard and a fundamentally different risk-management posture.
Ignoring registrant divergence. Two very different DNELs for one substance is a flag to investigate dossier quality, not a coin toss.

How to Find and Apply a DNEL: A Step-by-Step Guide