Abstract: A fire extinguisher with an actuation mechanism includes a fire extinguisher body filled under pressure with a fire suppressant. The actuation mechanism includes a pneumatically controlled activation piston assembly that functions to control the release of the fire suppressant until desired by the user of the fire extinguisher. The activation piston assembly includes a housing in which a piston is positioned. The housing includes a first end and second end. The first end of the housing is covered with a first cap supporting a spring interposed between the piston and the first cap, and the second end of the housing is provided with a second cap. The piston, under the control of balanced spring bias and pneumatic pressure, allows for time controlled release of the fire suppressant from the fire extinguisher body.