When combined, 着火 (zháohuǒ) creates a vivid and literal image: “fire has successfully attached itself” to something. This is why it perfectly describes the act of catching fire.
While 着火 (zháohuǒ) is a practical, everyday term, its importance is rooted in China's long history with fire as both a tool and a threat. Traditional Chinese architecture heavily featured wood, making entire cities vulnerable to devastating fires. As a result, fire prevention has always been a major societal concern. You will frequently see signs in temples, historical sites, and public places with phrases like “严禁烟火” (yánjìn yānhuǒ), meaning “No Smoking or Open Flames.” The word 着火 is what happens when these precautions fail. In contrast to the English “to be on fire,” which can describe a continuous state, 着火 often emphasizes the *start* of the fire—the moment of ignition. For example, you would say the forest 着火了 (zháohuǒ le) to report that a fire has just started. While it can also describe the ongoing state, its primary nuance is the act of catching fire. This is slightly different from the more scientific or literary term 燃烧 (ránshāo), which means “to combust” and describes the continuous chemical process of burning.
着火 (zháohuǒ) is a neutral term used in all contexts, from urgent, informal shouts to formal news reports.