Wikipedia:Reference desk/Archives/Science/2017 October 24

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October 24

Source of elements

In File:Nucleosynthesis periodic table.svg this graphic, elements 43, 84-88, and some others are a color that doesn't match anything in the legend. Where do these come from? Bubba73 ^{You talkin' to me?} 05:29, 24 October 2017 (UTC)

The brown/tan-ish color is "100% synthetic", according to the popup notes when hovering over those elements as the image description recommends. I agree the legend is deficient, and SVG-implemented image annotations are not as standard as the ImageAnnotator gadget. DMacks (talk) 05:35, 24 October 2017 (UTC)

Thanks, the SVG works but I had converted it to a PGN. Synthetic radioisotope helps. Bubba73 ^{You talkin' to me?} 13:59, 24 October 2017 (UTC)

Closed Room and extinguishing fire with halon

During a fire, can you still breathe when a halon fire extinguisher is activated? Or is it expected to aerate the room (train/plane) immediately after halon is used?--Hofhof (talk) 23:24, 24 October 2017 (UTC)

Neither. All people are expected to evacuate the room immediately. Only when firemen declare it safe should the air be exchanged and the room reoccupied. StuRat (talk) 23:35, 24 October 2017 (UTC)

And what if the fire is inside a plane or train? --Hofhof (talk) 23:48, 24 October 2017 (UTC)

You would stop the train immediately and evacuate, or evacuate to other cars. A major fire on a plane in flight is rather deadly, as there aren't many good options for dealing with it. Prevention is the usual course of action. For a small plane fire, usually just a smokey smell, they also land as soon as possible and evacuate. StuRat (talk) 02:12, 25 October 2017 (UTC)

Aircraft are one of the few exemptions where you will still find halon. Andy Dingley (talk) 02:54, 25 October 2017 (UTC)

• Depends on the halon. They're all asphyxiants, but halons (unlike CO₂ flood systems) are primarily a chemical agent. So they're used in smaller concentrations than CO₂. Halon 1301 was the favoured agent for flood systems, halon 1211 for hand-held extinguishers. Both are considered somewhat toxic and exposure should be restricted, and 1301 was favoured for flooding as it was somewhat safer. They are though safe enough that people can escape a space that has been flooded.

Halon is no longer used for fire extinguishers, except in some very narrow exceptions, owing to concerns over ozone depletion with CFCs (bromine compounds like the halons too). Halons are still used in some rare situations (I think WP was recently saying that they were completely banned, and there was edit-warring over this) - the Channel Tunnel is one. Flood systems have largely been replaced with CO₂. Halotron I is a non-ozone-depleting replacement for halon 1211 in hand-held uses and has similar toxicity - exposure should be limited, but it's better than being in a fire.

Older agents, notably carbon tetrachloride or Pyrene fluid were remarkably effective extinguishers, but quite evil for toxicity in confined spaces. They're chronically liver toxic for exposure to the fluid and acutely extremely toxic if the fluid is sprayed onto a fire, as phosgene is produced. This was particularly hazardous in sealed spaces, such as tanks - Pyrene extinguishers were fitted to them for a long time, then later only fitted externally. Even smoking near a spill of the fluid has been known to be immediately fatal. Andy Dingley (talk) 00:11, 25 October 2017 (UTC)