From: gay@sfu.ca   
      
   Libor 'Poutnik' Stříž wrote:   
      
   > Dne 08/01/2018 v 01:10 sinclair220@hotmail.com napsal(a):   
   >> On Monday, 8 January 2018 00:56:08 UTC+1, sincl...@hotmail.com   
   >> wrote:   
   >   
   >>>   
   >>> An interesting post Peter, but one question as a layman; Why should   
   >>> the instructions of the co2 detector recommend fixing it onto the   
   >>> ceiling? If butane is heavier than air, should it not be fixed to   
   >>> the wall? It could be of course, badly translated English from the   
   >>> Chinese manufacturer. Appreciate your advice. Rgds Sinclair   
   >>   
   >> I've found the answer; Butane is heavier than air but Co2 is lighter   
   >> and its Co2 gas that we are detecting. Apparently, Co2 detectors   
   >> should be fixed on a wall, not the ceiling because heat that stows   
   >> above will stop detection,   and the detector should be 15 feet away   
   >> from the source of heat. Rgds   
   >>   
   > CO2 is heavier/denser then air either,   
   > having about the same molar mass 44 g/mol as propane.   
   >   
   > But the point is - at the same temperature.   
   >   
   > Hot enough CO2 is lighter/less dense than cold air,   
   > and additionally, there is not only CO2,   
   > but the majority is nitrogen, and also water vapours,   
   > that further decrease the density .   
   >   
   > So gases need not to be very hot   
   > to be less dense than normal air at ambient temperature.   
   >   
   > The gas from a fire climbs up, not falls down.   
   >   
      
   But does anyone actually have CO2 detectors? Maybe the OP is really   
   talking about CO detectors. CO is slightly lighter than air, but I   
   would be surprised if the small difference were significant.   
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