Spotlight on Spontaneous Combustion – Linseed Oil
Hands up if you use linseed oil? Keep your hands up if you also know how to store or dispose of the rags used for the application process?
Linseed oil comes from the dried, ripened seeds of the flax plant. It’s a drying oil, which means it can solidify. Due to its versatility, it can be used on its own or blended with other oils, resins, and solvents as an impregnator and varnish in wood finishing, as a pigment binder in oil paints, as a plasticizer and hardener in putty, and in the manufacture of linoleum.
When linseed oil is used to finish wood (including some exterior deck sealers and wood stains), heat is generated during the drying process. This is because these oils don’t dry like paint (through the evaporation of a solvent or water). Instead, they dry through the same chemical process that generates fire – oxidation. This process generates heat and in some cases this heat may be sufficient to ignite the material it is on and then catch fire to anything nearby. This is called spontaneous combustion because it occurs as its own process without the need for a flame to be introduced.
For spontaneous combustion to occur, enough heat must accumulate so fire can start. You would never see a piece of furniture spontaneously combust because the oil oxidizes in open air, so the surface never even gets warm to the touch. But a pile of oil-soaked rags can. The bigger the pile, the greater the possible heat and the greater the risk. Temperature is also a factor. The warmer it is, the quicker the rags can reach ignition temperature.
Recommendations:
· Store rags in a non-combustible container (metal) with a close-fitting lid, away from the house and combustible materials
· Rags soaked with linseed or other drying oils may smoulder for several hours before flames are visible
· Rags used with linseed oil should be allowed to dry completely in a safe place, away from flammable materials. The best way to achieve this is to lay the rags out flat on a concrete driveway and allow them to completely dry off
Read more about these dangers in the following two news articles:
Source: Issue 23 – The Hazards of Linseed Oil (3/9/2015) – NZ Fire Service Research and Investigation Unit
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