This standard provides a uniform method for measuring the viscosity of flammable viscous liquids with flash points below 23°C (such as paints, varnishes, adhesives, etc.) to assess their hazards under specific transport conditions. The core of the standard involves determining viscosity by measuring the flow time of the liquid under specified conditions. This is typically performed using a device known as an ISO standard outflow cup (or flow cup), which has a nozzle of a specific diameter (e.g., 4 mm or 6 mm). During testing, a high-precision thermometer and stopwatch are used to ensure the sample is measured under constant temperature conditions (e.g., 23°C ± 0.5°C) and to accurately record the outflow time. The results obtained from this method are of significant importance for the classification, packaging, and transportation safety of hazardous chemicals.