The standard lays out the testing:
A quantity of liquid is poured steadily on a point on the top of the ME EQUIPMENT. The type of liquid, volume, duration of the spill, and
location (point) are determined through analysis. Test conditions that simulate the worst case for spillage shall be documented in the RISK
MANAGEMENT FILE.
After these PROCEDURES, the ME EQUIPMENT is to pass the appropriate dielectric strength and LEAKAGE CURRENT tests and is to show no signs of wetting of uninsulated electrical parts or electrical insulation of parts that could result in the loss of BASIC SAFETY or ESSENTIAL PERFORMANCE in NORMAL CONDITION or in combination with a SINGLE FAULT CONDITION (based on a visual inspection).
You have to determine volume, duration, height based on your assessment of worst case conditions.