Terminator 2: Judgement Day - You Can't See Halon Gas
When Arnold shoots the computer room door open clouds of billowy white gas appear and Dyson says it's the Halon fire system. Halon is a colorless gas. It was CO2.
In my opinion, I don't think halon is colorless. A few weeks ago, someone accidentally set off the halon system of my company's computer room, the whole area was like a big white cloud.
Whether you can/can't see Halon gas in reality is beyond the point. You should all think of it this way, lets say Cameron anticipated this. If I were him, I would NOT make the "pretend movie" gas in the room invisible nor would I put real Halon gas there for the following reasons:
1:Lets say he made it invisible, would you be more impressed? I wouldn't! It would look cheap and make-believe. Who would be convinced that Arnold is really walking through gas if you can't see anything?
2:Even if you cannot see Halon, seeing it in the movie looks really cool, especially when the swat team comes in with laser-guidance mp5's (my memory is not too good with what they held). The point is you can see the lasers well in smoke, thus looking cool.
3:In the unlikely case that Arnold might get hurt (as mentioned above) from any other kind of "invisible" or real Halon gas, if there was to be an invisible gas there.
4:Who cares what color it is? I looks fantastic coming from the ceiling anyway!
Does the color of the gas affect the story line? Does it make the viewer think, hold on, thats an error, or do you all have to research this issue to nit-pick T2? I don't see this as a slip-up, simply because it is the situation where you cannot improve on. What would you do? Visible gas, or unbelievable fake gas?
I served in the Mechanized Infantry at Fort Hood, TX. We rode around in the Bradley Infantry Fighting Vehicle, which is equipped with a Halon discharge system. Halon may be a gas, but when someone accidentally pulls the Fire Extinguisher pin, it forcibly blows a white powder into the crew compartment. this powder completely sucks all the oxygen out of the air and gives the guy sitting right next to the outlet a major head and neck ache from the force of its expulsion.
And yes, getting six fairly large, half-blind soldiers, complete with canteens, ammo pouches, weapons, flak vests, helmets and protective masks out of a very small (2' x 4') door can be done in a remarkably short amount of time.
I'm guessing they didn't really care because they figured if they used invisible gas the audience would think it was crappy so they used a harmless yet visible gas. It looks cooler than nothing. And then we turn to the "who really gives a crap anyway?" category which I think answers itself. But that is a good point about the gas being invisible, I'll give you credit for that.
Halon gas is also incredibly expensive to let off, I doubt Cameron wanted to pay for a colorless gas. Also, Halon is pretty toxic, not to mention most systems suck out the air in the room while discharging, which is why they don't install it in large offices - usually only a data center.
Another related point: Halon gas is not itself toxic; rather, it is the fact that it displaces the air that makes it dangerous (technically, it is an asphyxiant). So putting on gas masks wouldn't help - they only filter out harmful vapours, they can't compensate for the lack of oxygen in the air...
Any of the fire suppression technologies displace oxygen, and present an asphyxiation risk. I believe what gets filmed is water vapor created by releasing SMALL amounts of very cold gas, like CO2 from dry ice, into a high humidity air-space.
Just as odor is added to Natural Gas by energy companies for safety (so leaks will be detected by human noses), color could be added to a halon system's emission so humans would see to leave the area.
Halon gas is colorless, that's why the halon systems have alarms within the area of protection to get people out. The "gas masks" are breathing tanks (like scuba gear), and are necessary when halon systems cover a large are like that (for those unfortunately caught inside). As for the gas, they used something like CO2 because:
1. They can see it
2. It's fairly harmless (Arnie needed to walk through it)
3. It acts like Halon (CO2 isn't used normally because of storage problems)
I used to work on security / fire systems.
You are not seeing the halon gas. You are seeing the condensation of the water in the air as it makes contact with the cooled gas. The gas is cool because as the pressure is released (gas is discharged from the container) it decreases in temperature. Although in reality, this scenario would require air that is more humid than found in a climate controlled facility, it is not impossible to "see" the gas.
Halon gas is colourless, so is CO2, yet you can clearly the effect of letting off a CO2 fire extinguisher. This is because the sudden release of pressure cools the gas enough for it to start condensing, and so you get a white cloud. the same thing happens with halon. Next time you see a CO2 extinguisher being let off, look closely, and you will see small pieces of dry-ice form in the plume.
Halon is compressed gas in liquid form, it doesn't take the oxygen out of the air. Fire needs three elements; Fuel, oxygen and ignition. The Halon adds a forth element to the equation, breaking the chain but chemically reacting with the other agents.
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