At what temperature can fuel potentially auto ignite without a spark?

Fuel can potentially auto-ignite without a spark at a temperature known as the auto-ignition temperature. This temperature varies depending on the type of fuel. In the options provided, 450°F is an indicative temperature where certain fuels, particularly common hydrocarbons, can reach a point of auto-ignition when subjected to high heat without the need for an external ignition source.

At temperatures significantly lower than 450°F, the likelihood of auto-ignition is greatly reduced as the heat energy available is insufficient for the fuel molecules to reach the necessary energy state for combustion. Conversely, temperatures much higher than this threshold can lead to auto-ignition as well, but 450°F serves as a practical and common benchmark for many fuel types. Understanding this temperature is crucial for safety protocols, as it helps in assessing the risk of fire and designing systems that prevent unplanned ignition in environments where fuels are used.