Which federal law enforcement agency is NOT typically involved in fire investigations?

The Drug Enforcement Administration (DEA) is not typically involved in fire investigations. The primary mission of the DEA focuses on enforcing the controlled substances laws and regulations of the United States, targeting drug trafficking and abuse. While the DEA may occasionally investigate fires related to drug crimes—such as those that might occur in drug manufacturing or trafficking scenarios—fire investigations are generally outside of their standard responsibilities.

In contrast, other agencies like the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) have specific roles in investigating arson, explosives incidents, and the illegal use of fire-related items. The FBI can also be involved in fire investigations, particularly if there's a connection to federal crimes or terrorism. U.S. Postal Inspectors may engage in investigations when fires occur in or around postal facilities, especially if there is suspected criminal activity related to mail. Therefore, the DEA is clearly not aligned with the core functions of fire investigation, making it the correct answer in this context.