According to the regulations, filling portable containers should be avoided in which instance?

Filling portable containers should be avoided when located inside a vehicle or watercraft due to the significant risk of fire and explosion. The enclosed space poses a danger as flammable vapors can accumulate, creating an unsafe environment. In the event of a spark or ignition source, these vapors can ignite, leading to potentially catastrophic outcomes.

Additionally, the confined space limits ventilation, which is crucial for dispersing any fumes that could escape during the filling process. Regulatory guidelines prioritize safety by dictating that operations involving flammable substances be conducted in open, well-ventilated areas to minimize the risk of accidents.

Factors such as weather conditions or the presence of powered equipment can influence safety but do not inherently create the high-risk environment associated with filling containers in confined spaces like vehicles or watercraft. Thus, the choice regarding the confined area aligns with safety protocols that aim to prevent hazardous situations.