Can I add a substance that doesn't have a CAS number?

Yes — this is a new addition to the Substance Library. Open Add Substance and turn on the “This chemical has no CAS number” toggle. The form switches from the CAS/chemical-name search to a manual entry form: Chemical Name is the only required field, and underneath it you can optionally fill in Compound Data — Hazard Codes (e.g. H301, EUH070), Exposure Information (Method, Regulation, Limit Value), Toxicity Information (Result, Dose, Species, Exposure), and Ecotoxicity Information (Species, Result, Value, Duration) — all as optional add-a-row tables. This is meant for chemicals that genuinely don't have a CAS number, such as oxygen entered generically, proprietary blends, or in-house formulations.

Once saved, it shows up in your Substance Library table with “No CAS number” in the CAS column — any hazard codes you added still generate the matching GHS pictogram automatically, exactly like a CAS-based entry.

Important: you can't pull a no-CAS substance into an SDS through Section 3's regular Add Chemical search box — that box only searches CAS numbers and chemical names against the external chemical database, not your own library. To use a no-CAS substance in an SDS, either: (1) use Select Preset instead of Add Chemical in Section 3 — your no-CAS substances appear in the Substances tab there, ready to Add with just a Percentage; or (2) add it as a component when building a Mixture (Substance Library → Add Mixture), where it appears in the substance dropdown labeled “(No CAS number)”. Either way, it still needs an Actual Percentage like any other ingredient — only the CAS number itself is skipped, and the ingredient table simply shows a blank CAS ID for it.

One limitation: you can only pull a no-CAS substance into an SDS whose Product Type is Hazardous. Creating the no-CAS substance itself (or adding it to a Mixture) in the Substance Library isn't affected by any SDS's Product Type — that part works anytime. But getting it into a specific SDS requires Select Preset, and Select Preset only shows up in Section 3 when that SDS's Product Type is Hazardous — a Non-Hazardous product's Section 3 offers Add Chemical only, so a no-CAS substance can't be added to it. If you need to document a no-CAS chemical on a Non-Hazardous product, switch the Product Type to Hazardous first.