In which scenario can the heating devices be considered safe for containers?

Heating devices can be considered safe for containers when they maintain a surface temperature below 125 Fahrenheit because this temperature threshold helps prevent overheating and reduces the risk of ignition of flammable vapors or materials that may be present in the vicinity. It is crucial for safety regulations and best practices to ensure that heating devices do not reach temperatures that could compromise the integrity of the containers or create hazardous conditions.

The other scenarios do not adequately address the critical concern of temperature control associated with the safety of heating devices. For instance, heating quickly might lead to rapid changes in temperature that could pose risks, while insulation alone does not ensure that the external surface temperature remains safe. Additionally, simply using heating devices indoors does not inherently make them safe, as it neglects the importance of how hot the devices can get and the potential for fire hazards indoors. Thus, maintaining a surface temperature below 125 Fahrenheit is the key factor for safety in this context.