C9–C15 Heavy Aromatic Hydrocarbons

Solvent naphtha (petroleum), heavy aromatic (CAS 64742-94-5) is a petroleum cut rich in aromatic ring hydrocarbons in the C9–C15 range — alkylbenzenes, trimethylbenzenes, and naphthalene homologs. Aromatic solvents dissolve heavier and more polar grease residues that aliphatic distillates leave behind, which is why heavy-duty mechanic degreasers blend the two solvent families.

The aromatic content also drives the inhalation-narcotic profile of the parent mixture. STOT SE 3 (H336 — drowsiness/dizziness) at the ingredient level translates to the well-documented "solvent headache" reported after extended use of petroleum-based degreasers in poorly-ventilated garages. Acute aquatic toxicity is real (EC50 single-digit mg/L for daphnia and fish), which is the basis for the SDS aquatic classification when this fraction appears at meaningful concentrations.

For users: this is the ingredient that makes solvent-based degreasers smell aggressive and produces the dizzy/headachy feeling on prolonged use. Outdoor application, full stop.