Definition
The flash point of a lubricant is the lowest temperature at which its vapor forms an ignitable mixture with air when exposed to a small ignition source. It is a safety parameter, not a performance parameter, and is required for transportation classification and storage regulations.
Two test methods are used:
- Cleveland Open Cup (COC) — ASTM D92: higher temperatures recorded; used for lubricating oils and hydraulic fluids
- Pensky-Martens Closed Cup (PMCC) — ASTM D93: lower temperatures; used for fuels and solvents; more conservative
Typical flash point ranges:
- Mineral base oils (Group I/II): 200–240°C COC
- PAO (Group IV): 220–270°C COC depending on viscosity grade
- Naphthenic process oils: 180–230°C COC