"Intrinsically safe exhaust fans are critical response tools used by search and rescue teams and other responders for ventilation of confined spaces where hazardous conditions exist. Intrinsically safe is a term used to describe a condition that exists when a spark or thermal effect generated during normal functioning or specific fault conditions is unable to ignite a given explosive atmosphere. Intrinsically safe exhaust fans are constructed of a variety of materials that may include metals and plastics with fan blades that are generally made of aluminum, fiberglass, or plastics to ensure that they are non-sparking. These fans are available in many sizes and configurations. The two primary means of powering exhaust fans are electric motor or pneumatic (compressed air) motor."
Department of Homeland Security: https://www.dhs.gov/