Sanctioned classification axes for an **exposure or its agent** — as distinct from the disease-level nosologies in ``DiseaseClassifications``. This is the load-bearing distinction in this module. ``ILOCausativeAgentEnum``, ``ILODiseaseCategoryEnum`` and ``EUOccupationalScheduleEnum`` classify a *disease*, so they hang off ``Disease.classifications`` — note that even the ILO's causative-agent axis is a statement about which agent-indexed item a *disease* is recognised under, not a property of the agent itself. Everything here classifies the *agent or the exposure event* — "benzene is an IARC Group 1 carcinogen" is a statement about benzene, not about any disease benzene causes. Putting agent-level facts into a disease-level slot would assert, wrongly, that the disease itself carries the hazard classification. These enums are therefore reached through ``Environmental.exposure_classifications``. Each axis below is an independent, published standard; they are deliberately separate enums rather than one blended vocabulary, because an exposure has a value on several of them at once (chronic + inhalation + chemical + IARC Group 1 is a normal, non-redundant description of occupational benzene). These annotate an exposure that dismech has already grounded to ECTO/ExO via ``Environmental.exposure_term``. They do not replace that grounding — ECTO post-composes the exposure event itself ("exposure to arsenic in water via ingestion"), while these axes record the regulatory and toxicological classification of the agent and the exposure's shape. Where an ECTO term already encodes the route, the ``exposure_route`` value simply makes it queryable without parsing the term label. Scope note — carcinogen classifications. Only the IARC Monographs classification is encoded here. Three national systems classify the same agents on parallel scales — the US NTP *Report on Carcinogens* ("known to be a human carcinogen" / "reasonably anticipated to be a human carcinogen"), the US EPA IRIS cancer descriptors (five weight-of-evidence descriptors), and the ACGIH TLV carcinogenicity notations (A1-A5). They are deliberately **not** encoded: they largely re-rank the same evidence, and carrying four near-parallel scales invites curators to assert an NTP or ACGIH listing they have not checked. IARC is the WHO/international instrument and is the one cited in the occupational literature dismech curates. If a national listing is the specific point being made, state it in the assignment's ``notes`` with its source. Also deliberately not encoded: the GBD (IHME) environmental and occupational risk-factor hierarchy. It is a genuine sanctioned classification and would fit this module, but its exact Level 2 / Level 3 label set could not be verified against a primary source when this module was written, and transcribing an approximate hierarchy would defeat the purpose. Left for a follow-up that works from the GBD capstone appendix.