How much heat does gunfire give off?, Rate-of-rise fire alarms and you Options

[Kagetenshi]

So I was reading the NFPA codes for fire alarms, and I happened upon a type of fire alarm, the rate-of-rise alarm. This alarm triggers whenever the temperature in a room rises faster than a predetermined rate. What sort of runner activities would make the room temperature rise faster than reasonable for day-to-day use? How much gunfire would be required per given room volume?

~J

[Rev]

That is a cool question. Hope the gun freaks have an answer. :)

I don't know about guns, but I know that a very small paper fire will heat up a room quite quickly.

When I was in college some friends showed up in thier (lucky me) dorm living room area (was one of those with four small two person rooms and a common area in the middle) very drunk.

One of them decided to wrap himself up in toilete paper like a mummy.

Another decided to light the toilette paper on fire.

So maybe half a roll of toilette paper burning for 30 seconds or so as drunken fools tried to put it out with handfulls of water and other ill considered means.

The room must have been 120F by the end, and pretty smokey.

Curiously the smoke alarms never went off despite a good two foot thick layer of smoke rolling along the hallway ceiling. Guess they were optimized for burning pop-corn or something.

The heat suprised me. Guess I had never been in an enclosed space with a fire before.

Anyhow any sort of explosive could heat a room up, as would a cutting torch.

[Dashifen]

No offense intended by I needed the laugh I got from that story :D Thanks! Can you imagine how interesting things could get with an elemental manipulation to control temperature -- no actual flames, just to control the temp. Localize it around the heat-detector and set of the sprinklers -- instant water damage to Corp Building A :)

Edit: spelling

[Raygun]

God, that is a good question. I have no idea. I guess it would depend on what the predetermined rate-or-rise is, what types of firearms are being fired (more powder = more heat) and whether or not those firearms were suppressed. The heat absorbed (and radiated) by the firearms themselves are going to make some difference as well.

Honestly, I think you'd have to do quite a lot of shooting to raise the temperature of a room any significant degree, unless the room were very small and you were spending far too much time in it. Obviously, smaller rooms are going to warm up faster, but if those rooms have windows, plumbing, equipment, etc... that room is going to have a larger range of temperature fluctuation than a room that is temperature controlled pretty tightly, like a NOC or something of that nature.

To give you some idea, I recently put 120 rounds through my AKM in about four minutes. By the time the third mag was gone (90 rounds), the metal parts around the handguard made it uncomfortable for me to hold the rifle bare-handed. After the last magazine, I did manage to burn my hand a little. I would guess that the barrel was up over 350-400 degrees by that point, possibly much hotter than that.

[Austere Emancipa...]

Figured it wiser to wait for word from someone who might actually know. Since no definitive answer as of yet...
I think the heat radiation from hot firearms is not going to change temperatures enough to trigger such an alarm, in a room of any size, even without any ventilation. The main source of heat would be the burning powder and hot gas that escapes the muzzle -- so like you said, suppression will likely make a huge difference.

My (totally uneducated) guess is that with 30 rounds of rifle caliber ammunition you just might be able to raise the air temperature of a very small (2 meter cube), unventilated room by a degree or two C momentarily. If you fire off a mag full auto, you'll certainly raise the air temperature around the muzzle (a meter in any direction) by several degrees with little or no ventilation.

I guess it largely comes down to exactly how the temperature trigger works -- can it instantaneously pick up air temperature changes, or does it have to be warmed up (as with a mercury thermometer)? Large muzzle blasts certainly raise air temperature near the muzzle for a moment, but the amount of heat generated is rather small and will dissipate quick. Just a few unsuppressed rifle shots near an accurate alarm system, which keeps track actual air temperature with no delay, could easily set off the alarm, I suppose.

To those of you who might give a damn but are too lazy to Google, a short list of propellant weights in some common cartridges:

5.56x45mm NATO M855 (representative of standard ammunition for ARs and LMGs) -- ~1.7 grams
7.62x51mm NATO M80 (representative of standard ammunition for some Sporting Rifles and MMGs) -- ~3 grams
9x19mm Luger M882 (representative of standard ammunition for some Pistols and SMGs) -- ~0.4 grams

Someone might be able to come up with how much heat energy those amounts of burning propellant powder can produce -- I doubt it's a whole lot, especially with much of that becoming kinetic energy. But when you start going cyclic, there's some real warm-up potential in there. 100-round belt of MMG ammo = ~300 grams of burning powder.

[Cray74]

I'd say figure out the muzzle energy of a bullet, double it to represent energy left in the gun and shooter, and compare that to the heat capacity of air in the room.

Raygun, can you supply some assault rifle muzzle energies in foot pounds or joules?

[RangerJoe]

I'm about to leave work, so I don't have time for the back-of-the-envelope calculations. What you want is some quick and dirty thermo. A speedy google search reveals the following gem:

The chemical energy stored in modern gunpowder comes to about 189 foot-pounds per grain of powder.

From: http://www.z-hat.com/Efficiency%20of%20the...0300%20Hawk.htm

That should be the key bit of info you need. Subtract out the KE, and you'll get a rough estimate of energy going into heat (work done by the expansion of hot gases? whatever....) From there, you can figure out the heat increase of a room of a given volume.

endnote: yes, I know better than to really believe information acquried from any site that uses comic sans as its font.

[Austere Emancipa...]

Here are some muzzle energy figures for common cartridges, in foot-pounds cause I've got a Guns & Ammo at arm's reach...

Assault Rifles ~ 1100 - 1600 ft-lbs, although some could be up to ~2000 ft-lbs (such as the 6.8mm SPC).
Sporting Rifles ~ 2000 - 3500 ft-lbs. Could be a lot higher, but I doubt the 9S Damage Code of Sporting Rifles would represent anything heftier than a light .300 magnum.
Light Pistols ~ 200-300 ft-lbs. It's hard to tell exactly how piddly-ass these are supposed to be, but that's basically between .380 ACP and .38 Special.
Heavy Pistols ~ 500 ft-lbs and up up up, into the ~3000 ft-lbs range.
Shotguns ~ 1500 - 3000 ft-lbs

[Austere Emancipa...]

Assuming 190 ft-lbs per grain of powder, you could get 8740 ft-lbs of energy out of the 7.62x51mm M80. ~2500 ft-lbs of that goes into muzzle energy, and some small amount goes into working the action. That leaves 8000+ ft-lbs of heat, some of which is absorbed by the gun and released slowly. So maybe 4000-6000 ft-lbs is quickly released into the air. (Which is not-very-surprisingly exactly twice the muzzle velocity like Cray74 suggested at first.)

That's with an error margin of +/- 95%, of course.

[Cray74]

Alright, let's work with 3000ft-lbs, which is 4000 joules, representing a high-end estimate for weapons heat release. Doubled (4000J in the bullet, 4000J in the gun), that's 8000 joules per round, which'll all end up as heat eventually.

For a generic 1000 cubic foot room, or 28 cubic meters, at STP there's 36.4 kilograms of air.

The heat capacity of air is 1000 joules per kilogram per degree K (or C).

So, it will take 36400 joules to heat up the air in the room by 1C.

That's 9 rounds from 8000J weapon to heat up the room by 1C.

At 1600J per bullet, that's 45 rounds to heat up the room by 1C. Firing off 1000 of those rounds in 3m x 3m x 3m room will heat it up by 22C/40F.

[Austere Emancipa...]

[Kagetenshi]

Keep in mind that the change in air temperature doesn't have to be lasting, just fast.

~J

[Austere Emancipa...]

Then your real problem will be discharging weapons near the thermometer, not actually raising the overall room temperature. Firing a rifle right below such a thermometer might get some of the very hot air (mixed with the propellant gases, or maybe even still-burning powder if you tend to pack unsuppressed Barretts indoors) directly inside the thermometer, which might then register a sudden change from 20 degrees C to 100 C and then quickly back down to 21 C. Which would most likely trigger the alarm, assuming the system can indeed monitor actual air temperature, instead of requiring heat to be transferred from the air into the thermometer.

Most of the time, you'll probably be firing your guns in areas where the connected air volume will be quite massive (several rooms connected by hallways), and there's nearly always some level of ventilation, so actual room temperature rise would only occur in extreme cases and is probably not worth your while to be concerned with.

[mrobviousjosh]

My largest concern, the way these alarms are worded, wouldn't be the amount of gunplay but the number of people in a given space. For example, think about a small car. One or two people and you may not have to run your airconditioner but you put 7 in it and you're praying for it. In other words, if security/runners/etc. were in a room within the timespan of a minute, how much would their sheer body temperatures alter the room's. Anyway, the weapons question is a good one and, unless someone's a gun specialist who studies 'em, other than heavy weapons/maybe SMGs and such, I don't think handguns would raise a room's temperature much more than a person's body would.

[McGravin]

So the general consensus is that, unless you're firing a gun on full auto within a meter or two of a rate-of-rise fire alarm, the room would have to be relatively tiny and poorly ventilated to set off such an alarm.

Just my opinion, but it seems like common sense that any building advanced enough to have ROR fire alarms would also have decent enough ventilation. While it would be something awesome from the GM's perspective to throw at the players, it seems like an unlikely event at best. In fact, it seems just as likely that burning powder and expelled gasses would set off a normal smoke alarm.

Edit: I don't think any reasonable number of bodies would generate enough heat in a short enough time span to trigger a ROR alarm. Keep in mind that they are rate-of-rise, meaning that if you raise the temperature by 20 degrees in an hour, it wouldn't do a thing, but if you raise the temperature by 20 degrees in a minute, it would trigger.

[mrobviousjosh]

[Necro Tech]

Actually shutting down ventilation can heat up a room very rapidly. To combat boredom at work one day, we decided to measure the temperature change in the shop just by shutting the front door. (and killing the breeze) In 60 seconds, +3 F. In 120 seconds, +7. In 180 seconds, +9. It levels off but in 15 minutes the temperature gains a total of + 19 F. Large office buildings that are undergoing HVAC repair get damn near unbearable in as little as 30 minutes with a temp change of 15-25 degrees. I'm cruising around in T-shirt and shorts while the cubbies look like they are near death. Like previously stated, it all depends on how much change and how fast is considered abnormal.

[Kanada Ten]

Very sensitive, advanced sensors and processors could measure temperature change and determine types of weapons being fired, number of targets, direction of target movement, and so on. The change need not approach a single degree change as they could filter out the various rises and decreases much like sound sensors could. Combined with other types of sensors, this "Delta T" sensor could become another weapon in the security system arsenal.

[Snow_Fox]

speaking from experience, more modern arms, unless you're on full auto shouldn't be a problem. (and if you're on full auto you don't need to worry about fire alarms 'cause people will hear the guns.)

To give an idea of my experience, 5-6 shots of my brown bess (black powder musket) and the barrell is too hot to handle without something between my skin and the barrel.

My enfield bolt action- the barrell is enclosed in wood, I have never had it be too hot to handle.

My berretta handgun-more likely what runners will use- the barrel is uncomfortable after maybe 2-3 clips (10 shot clips) and you can feel it when you cock it, but you don't feel it when you're holding it by the grip.

BAD THING FOR SUCH SENSORS-the spent brass will be hot and you'll be leaving a trail of little hot brass casing behind you. If you take time to pick them up where on your person will you carry them? in a pocket< they are hot kids.

[Hague]

Brass catchers are wonderful things. :) As is caseless ammo.

What model Enfield? Just curious.

[Dice]

From this article:

[Snow_Fox]

[Hague]

No.1 Mk III? Is it wire wrapped? I've got one of those. With the bayonet attached, the rifle should qualify as a polearm. Its like 16 or 18 inches of steel on the end of the rifle. Mine's from Ishapore, though, friggin Indian. I'm considering getting one of the No. 4 carbines that I've seen advertised a few places. Just wish that .303 ammo wasnt so friggin expensive. You can feed a FAL about 3 times as much for an equal $ amount vs .303.

If you do get a Lebel, you arent going to actually fire it, are you? I dont trust any firearm made by the French. After all, to get adopted for French army service it only has to survive being dropped once.

[Snow_Fox]

wire wraped? I don't understand.
I've seen a chau-chat fired, if that abomination can survive nearly a century a lebel should. It was a well made rifle but the bitch of it was the magazine was horizontal along the barrell, like a shotgun, each time you fire it, the balance point chnaged, making accurate rapid fire difficult. and reloading slow because you couldn't just run a clip through it.

Watch the 20th c. battle scene at the start of Brandon Fraser's The mummy, they have Lebel's and Fraser is carrying a couple of reloads in his teeth, in the voice over he said it wasn't somethnig from the director, it was just the easierst way for him to get bullets quickly into the gun.

[Raygun]