SDS Section 10: Stability and reactivity

The section that assumes the product itself is the variable

Most of the sheet is written as though the chemical is a fixed thing and the only question is what it does to a person. Section 10 drops that assumption. It describes the product as something that can change — warmed in a sunlit yard, left in a part-empty drum, contaminated by whatever the container held before, sitting long enough for a stabiliser to be consumed.

REACH Annex II frames the whole section that way, and it is worth reading the framing sentence rather than the six headings: the section shall describe the stability of the substance or mixture and the possibility of hazardous reactions occurring under certain conditions of use and also if released into the environment, including, where appropriate, a reference to the test methods used. Two obligations hide in that sentence. Section 10 is one of the very few places on an EU sheet where the author is asked to say where an answer came from, and the scope is not limited to the workplace.

Six headings, three jobs

The subsection titles are identical word for word in REACH Annex II, OSHA’s Appendix D and UN GHS Annex 4 — unusual across the sixteen sections, and the reason the jurisdiction switch on this page changes the content of each row rather than its label. The six divide naturally into three groups.

The product on its own — 10.1, 10.2, 10.3

Reactivity, chemical stability and the possibility of hazardous reactions describe behaviour that needs no second chemical present. 10.2 carries the reference conditions: stable or unstable under normal ambient and anticipated storage and handling conditions of temperature and pressure. That phrase is what makes “stable” a meaningful word. Without it, “stable” is a claim no supplier could support, since everything decomposes somewhere.

10.2 also asks for two things authors routinely drop. Any stabilisers which are, or may need to be, used — a monomer whose inhibitor is consumed over time is a different product at month eighteen than at month one. And the safety significance of any change in physical appearance, which is the one instruction on the sheet a non-specialist can act on without instruments: if it has gone cloudy, yellow or crystalline, the sheet should say whether that matters.

10.3 then asks whether the product may react or polymerise, releasing excess pressure or heat — and, crucially, under what conditions. A polymerisation warning without its trigger cannot be designed against.

The product meeting something else — 10.4 and 10.5

10.4 is physical and 10.5 is chemical. The EU list under 10.4 runs temperature, pressure, light, shock, static discharge, vibrations or other physical stresses; UN GHS Annex 4 opens the same list with heat and omits light. OSHA gives three examples — static discharge, shock, vibration — and stops.

10.5 is where the EU text is most demanding. It asks for families of substances or specific substances, and it names five families outright: water, air, acids, bases, oxidising agents. It also defines what makes an incompatibility worth reporting — an explosion, a release of toxic or flammable materials, or a liberation of excessive heat. And both 10.4 and 10.5 close with the same clause: if appropriate, a brief description of the measures to be taken to manage the risks. That clause is what separates the EU section 10 from a list.

The EU-only thread: desensitised explosives

One requirement runs through both halves of the section and exists on the EU side only. A product held stable by a desensitising agent rather than by its own chemistry attracts named duties in 10.2 and 10.4 that Appendix D does not carry. Subsection 10.2 asks for the shelf life, for instructions on how to verify desensitisation, and for a plain statement that removal of the desensitising agent will turn the product into an explosive. Subsection 10.4 then asks for the measures that prevent that removal happening unintentionally, and for conditions to avoid where the product is not sufficiently desensitised. For this family, section 10 is not commentary on the classification — it is the instruction that keeps the classification true.

What comes off it — 10.6

Known and reasonably anticipated hazardous decomposition products from use, storage, spill and heating. Note spill — the EU list is one item longer than the UN one, which names use, storage and heating. And note the routing instruction that closes the subsection: hazardous combustion products go in section 5.

Incompatibility is a relationship, not a property

The structural weakness of 10.5 is that it is written per product, but used per pair. A drum has no incompatibility on its own; it has one with the drum beside it. Annex II acknowledges this in 10.1.2, which says incompatibility is determined against the substances, containers and contaminants the product might be exposed to during transportation, storage and use — a test about circumstances, not about the molecule.

This is why two honest suppliers produce different 10.5 entries for the same substance, and why reading one sheet answers half of a two-sheet question. Our storage compatibility checker exists for the other half: it takes the pair rather than the product. The underlying reactive-group data is visible on the substance pages, for example at acetone, section 10. The families Annex II names at 10.5 are also the families a store is laid out around, which is why the class pages for water-reactive substances and oxidising substances collect the pairings those two entries generate most often.

How section 10 connects to the rest of the sheet

• The classification in section 2 is what obliges section 10 to say anything at all: a self-reactive or water-reactive classification is a promise that 10.3 and 10.5 will explain themselves.
• Section 5 takes the combustion products that 10.6 explicitly refuses.
• Section 7 turns 10.4 and 10.5 into storage instructions; Annex II 7.2 asks specifically how to manage risks from incompatible substances or mixtures, and requires consistency with section 9.
• Section 9 holds the numbers section 10 argues from — flash point at 9.1(h), auto-ignition temperature at 9.1(i) and decomposition temperature at 9.1(j). The temperature belongs to section 9; what the decomposition produces belongs to 10.6.
• Section 13 inherits the problem: a product that reacts with water or acid constrains how it may be treated, not only how it is stored.

What a good section 10 looks like

1. Does “stable” come with its envelope? 10.2 and 10.4 have to be read together. If 10.2 says stable, 10.4 should say stable within what — a temperature, a light condition, an absence of shock.
2. Can you act on 10.5 without a second document? Named families, the hazardous outcome they produce, and — under the EU text — the measures that manage it. A bare list of chemical names is a research task handed to the reader.
3. Do the gaps explain themselves? REACH requires the reasons where a property does not apply or the data do not exist; OSHA requires a clear statement that no applicable information is available. A field that says nothing fails both, and a field that says “None known” without saying on what basis is barely better.