[Cob] Linseed oil and Iraq

[Mitch Ventura]

"ANOTHER NOTE!! Rags soaked in linseed oil will readily burst into flames 
(spontaneous combustion) as they are drying. When you are done with the 
rags, spread them out flat in the sun in a non-flammable area and weight 
them down with rocks until they have dried, then place them in a tightly 
covered metal garbage can until they can be disposed of."
   
  Am planning on building a cob house in the subtropics after I finish my tours of duty as a firefighter in Iraq. My original plan was an adobe house, but luckily stumbled on cob technology while browsing the Internet a couple of months ago.
   
  As to linseed see oil and spontaneous combustion... not blowing my own horn, but have been a professional firefighter for many years and have college-level courses in fire theory, so i do know something about this particular subject. If one is not interested in technical explanations, please do not continue reading .
   
  Only certain oils will spontaneously combust. Contrary to popular belief, and one that, unfortunately, is even promulgated within the fire service, rags with motor oils will not burst into flames; their risk is due to adding to the surrounding fuel load in any area that may become involved in fire. The technical reason is that there must be unstable double atomic bonds present (carbon dioxide has stable double bonds and that is why it does not readily decompose). The decomposition of unstable bonds is brought about, in the case of oils and other common combustibles, by oxidation by the oxygen in ambient air. This always creates some heat, but is extremely insignificant on an individual basis. However, when there are millions and millions of reactions taking place, then heat can build-up.
   
  However, for heat to build-up to any significant amount, it has to be protected from cooling. A linseed oil-soaked rag in a corner inside a building, away from drafts, or inside a can with a loose lid (letting in more oxygen to replace that which is used-up in the reaction that ends-up breaking-down double bonds) could act as a "heat sink"; there is also trapped air with the folds of the rag... therefore, a statement about stretching out a rag is quite valid (no folds = no room for trapped air... the air below a stretched-out rag is not stagnant and will migrate "outside").
   
  Every combustible item, including linseed oil, has an ignition point. This is the temperature at which something will set on fire without being in contact with a flame or spark. So even with heat build-up, there has to be enough to set the oil on fire.
   
  Then, again if it does burn it has to be large enough of close enough to other combustibles to cause a significant fire.
   
  Can some products spontaneously combust in a few seconds? Yep! Will linseed oil do so? Nope! It takes quite a while.... but Shannon is right about the fact that it may self-combust. (Why take a risk?)
   
  So, what is the likelihood of you linseed oil-soaked rag setting on fire/ Not much. However, I never went to a house on fire where the owner said, "Darn! That's the second time my house has burned-down." There is always a first time, so I would never let these rags set in a folded rag near anything else that is combustible... just in case I am one in a million cases of unlucky chaps. (Margarines, butter, fats, and other "oily: substances may also self-combust since they have unstable double bonds... however, there is not much risk in leaving your kid next to the dairy products in the store.)
   
  Looking forward to seeing more info on cob construction.
   
  Ma'a salama.
   
  Mitch
   
  P.S. Shannon, I really appreciate the fact than an expert like you is providing information in this Forum. Have learned quite a bit from you to date. I hope that my information is an embellishment to your statement about self-combustion and not a detraction.
   
  P.P.S. Being that many Iraqis are unemployed, and the wonderful clay-enriched soils in my area, I have told quite a few Iraqis on base about cob construction and not one has shown interest. They see it as a step backwards. (I have seen the same in subtropical Mexico where the wealthy would not dream of using adobe or an adobe-looking design whereas in California their economic counterparts have, at least, houses that resemble adobe. In the past ten years, that trend has been changing in Occidental Subtropical Mexico, but more often seen with weekend cabin retreats, although sometimes in the city... the middle and lower middle classes, like many Iraqis,  see mud construction as a step backward... LOL but without a smile.)
   

       
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