How long can a portable heater be on before it causes a fire?

The duration a portable heater can be on before causing a fire varies based on several factors, including the heater's type, its condition, and the surrounding environment. Generally, if a heater is used according to manufacturer guidelines and is placed away from flammable materials, it can run safely for extended periods. However, leaving it unattended or using it inappropriately increases the risk of fire. It's crucial to follow safety precautions and turn off the heater when not in use.