Part 1: Its not really a gun
The Alpha Complex Saftey and Security (ACSS) project provides R&D funding for development of devices to help secure Alpha Complex against events that do not directly involve Commies, Mutants, or Traitors. Although fires are rare in the synthsteel and plasticreet sectors, there are still electircal and chemical fires to be concerned about. For this, troubleshooter teams on ACSS missions can be given the new Fire-Extinguisher Gun.

Part 2: Really, its not
The gun has a dual-canister loading system with a swing-arm nozzle. Swinging the nozzle mechanism connects the release valves to the dual canisters and prepares the gun to blast a fire-extinguishing foam cocktail. The two chemicals react to form a powerful anti-oxidizer that can seriously dampen electrical, chemical or normal fires.

The gun has a realistic range of 5 to 20 meters (15 to 60 feet), which isn't a huge distance when dealing with fire. This is mainly due to the speed of the chemical reaction and the power behind the firing mechanism.

Part 3: I swear to you it isn't
Once the trigger is pulled, a jet of mixing chemicals shoots out. There isn't any way to really control the distance the spray fires, its mostly just a "keep pulling back until it hits something" approach. The jet is fairly forceful, being under heavy pressure in the canisters, but will only last 12-15 seconds.

Part 4: Well, I suppose you COULD use it as one

• The chemicals act as a topical neurotoxins until they are finished reacting with each other, after which they are pretty inert and harmless.
• There's no real chance of getting hit by the spray if you're holding the gun, the blast is very tight. A headwind might be problematic.
• The toxic agents are fast. Very fast. A small amount will cause hallucinations, a larger dose will cause temporary dementia.
• Ingenstion is fatal. Neurological seizure and heart failure is guarenteed for any level of internal intoduction whatsoever.
• Removing the canisters at any point after locking the nozzle on is a very, very bad idea. The nozzle opens the top valves, which do not re-seal. They are also under tremendous pressure. Even after firing the extinguisher, there is still going to be remnants in both canisters. R&D will tell the troubleshooters to return the gun with the canisters locked to the nozzle.