This stuff is not a product and does not have a supplier, so it doesn't need to have a safety data sheet and there is no one to write one.

All you can do is take what you know or can find out about its chemical composition and physical state, identify the corresponding hazards, and write a COSHH assessment based on that.

COSHH assessments don't have to be based on safety data sheets, even though the form you use for them may imply this.

The hazards of exhausts are very different from the hazards of the fuels they are emitted from because they are chemically very different.

Edited by user 01 October 2025 16:00:58(UTC)  | Reason: added last para

You not only have the fuels to consider but any additives such as AdBlue / biodiesel / ethanol along with lubricating oils from the engines, anti-freeze & other coolant additives which can all end up passing out of the exhaust system.

Then there are considerations around the combustion process - excess air / insufficient air / temperature.

If there are multiple vehicles you then add further variability for glow plug / spark plug condition.

A fully definitive answer as to the "soot" composition would only come from a full chemical analysis.