What term describes a person who starts a fire in a building and releases poisonous gas?

The term that accurately describes a person who deliberately starts a fire in a building is "arsonist." An arsonist is someone who commits the act of arson, which involves intentionally igniting a fire with the intent to cause damage or harm, including endangering lives through the release of toxic gases. This can lead to severe consequences not only in terms of property damage but also in harming individuals who may be exposed to those hazardous conditions.

The other terms listed do not specifically identify someone who sets fires. A catastrophe refers to a significant disaster that causes extensive damage or suffering. While a criminal is a broad term used to describe anyone who engages in illegal activities, it lacks the specific focus on fire-related offenses. A terrorist typically refers to someone who uses violence or the threat of violence to intimidate or coerce for political or ideological purposes, which may include arson as a tactic, but does not solely define the act of setting fires.