Wikipedia:Reference desk/Archives/Science/2019 April 15

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April 15

Ocean rocket launches.

How do ocean rocket launches affect-effect the atmosphere of Earth? — Preceding unsigned comment added by 2600:100D:B066:D7C5:5579:804:B6BA:FDF (talk) 17:38, 15 April 2019 (UTC)

Same way as non-ocean ones. Most launch sites, except the Russians, are (for safety reasons) on the coast anyway. Most large launch vehicles are hydrogen-oxygen fuelled, so their combustion is pretty benign - although there's an energy cost in preparaing both propellants. Solid rocket boosters are using ammonium perchlorate oxidisers with aluminium as a fuel (and some rubber as a binder), so although they're less clean, again their main impact is in the energy which goes to produce the precursor chemicals. A few rockets, military, smaller and the Titan II booster use mixed oxides of nitrogen as an oxidiser, which is unpleasant stuff and powerfully acidic. However on the scale of oceans, and given how few rockets we launch, the overall effects are small. You could calculate the numbers to check, but I'd be interested to compare the total fuel burn of a rocket launch, vs. the driving habits of the large number of spectators watching it. Andy Dingley (talk) 19:16, 15 April 2019 (UTC)

Foam dropping on the roof in the Notre Dame fire

As the idea of aerial water drops for Notre-Dame de Paris fire was discarded, how effective would foam drops have been instead (or similar less damaging fire retardants)? Don't know if the option of non-water fire retardants has been considered as well. 212.180.235.46 (talk) 22:02, 15 April 2019 (UTC)

Firefighting foam is usually created by mixing a foam concentrate into the hose stream at the pumper, and it becomes foam as it passes through a nozzle of appropriate design. Occasionally the pumper also adds compressed air to the hose stream to enhance the foam generation at the nozzle.

I have never heard of a firefighting aircraft equipped with either a nozzle or a pump; such aircraft work by simply dropping water or a fire retardant solution on or near the fire. They have no ability to generate foam. Jc3s5h (talk) 22:19, 15 April 2019 (UTC)

The Notre Dame spire fire was a "fully developed" structure fire. At this stage in a fire, there is often no real way to extinguish it: the tactics used by a fire fighting team are largely designed to prevent the flame from spreading.

You can read more about structure fire fighting at the data and tools section of the National Fire Protection Association website.

A few years ago, NFPA actually published an entire article on a misting fire safety system for St. Patrick's Cathedral, in New York City. They emphasize that the key is to flood the air and the environment early - using nitrogen and water mist to displace oxygen and cool the wood structure before ignition even happens.

"By the time hoses and equipment could be lugged up the spiral steps during a fire event, however, it would likely be too late to mount an effective attack on an attic fire, say fire officials. “Our best estimate is it would probably take somewhere between 20 and 30 minutes before we could get water on the fire if it was up in that area,”..."

Twenty to thirty minutes after ignition is, regrettably, usually too late to save a structure. Even if you can extinguish the flame, the building has already been structurally destroyed by the immense heat. Even parts of the building that have not been directly engulfed by flame have been exposed to radiant heat "flux". Here's a whole book on Fire Safety Challenges of Tall Wood Buildings. The direct exposure to line-of-sight infrared (heat) radiation is often enough to destroy the structure.

Aerial flame retardant will not extinguish a fully-developed structure fire - that's simply not what it is designed to do. For example, the pink gunk that you see Cal Fire Air Attack dropping out of planes and helicopters is "used to slow or retard the spread of a fire" - not to extinguish it.

Nimur (talk) 00:53, 16 April 2019 (UTC)

Firefighting foam is primarily meant to suppress a fire arising from flammable liquid, by coating the surface and preventing the formation of flammable vapor. It does little to cool and suppress a deep-seated structural fire in materials with some mass - water is the only effective means of stopping such a fire. A fire burning in mass needs masses of water to cool it, since a film will quickly dissipate and heat + fuel+ oxygen = fire again. Acroterion (talk) 01:05, 16 April 2019 (UTC)

And for the enthusiastic or innovative entrepreneurs in our audience: California's Fire Technology summit took place about a week ago; and the 2019 European Fire Safety Engineering conference is next month. As much as I love technology and fire-safety, we all want to have fewer fires in the first place. Everyone should do the stupidly obvious things to help with fire-prevention, because statistically, most fires are caused by stupid, easy-to-resolve problems. Fires are a lot easier to prevent than they are to extinguish.

Free resources and coloring books for kids: every week is fire prevention week.

Nimur (talk) 01:18, 16 April 2019 (UTC)

To second Nimur, the point of sprinklers isn't necessarily to put a fire out, it's to react early, sound the alarm, to suppress fire growth until enough resources can be brought to bear to extinguish the fire, and to give building occupants time to safely evacuate. Happily (if that word can be used unironically in this case), life safety wasn't the primary concern in the Notre Dame fire, but it is in most other cases.

The movies where water comes out of the whole ceiling in a fire are nonsense - you want maximum water and maximum pressure at the point of need, not spread out over the whole place (causing water damage in the process), and you can't have 6" pipes all over the place, so individual heads go off when the heat reaches them, and no more. And that water is most definitely not clean - it's usually black from sitting in pipes for years. Acroterion (talk) 01:44, 16 April 2019 (UTC)

Certainly possible, but no longer necessary. Many sprinkler/deluge systems now have pressurized gas in the pipes to prevent accidental discharge in case the pipe or head gets damaged. The water stays in a reservoir or pumping station and may be discharged/recharged. Matt Deres (talk) 13:40, 16 April 2019 (UTC)

Back during the September 11th attacks I wondered if you could rig up a cruise missile full of halon to attack a fire. Of course, it would have to do all sorts of probably undoable things like dump most of its fuel at the last minute, then coast to a gentle-ish landing before spraying the stuff out. But ... do you think it's conceivable, or just nuts? Wnt (talk) 04:07, 16 April 2019 (UTC)

with respect. :-)) Richard Avery (talk) 12:47, 16 April 2019 (UTC)

On the topic of the original question, this morning (rather, Monday evening), L'Express ran an article, Pourquoi le largage d'eau est impossible (Why aerial water drop was impossible...). Nimur (talk) 16:07, 16 April 2019 (UTC)