Uponthesquare

Just a little correction to a blog by Chris (14:38:00 May 12th)

The MSDS provides lots of good info. Chris mentions some things it includes. They include the flash point. The flash point is not quite as he describes. [I am a chemist, have measured flash points, and thus am qualified to answer this concern.] The flash point is NOT the temperature that spontaneous combustion will occur. It is the temperature at which a fuel/air mixture will ignite when exposed to a small ignition source (usually a flame about 2mm diameter) for a specified period of seconds in a closed container.(about 2-5, as I recall) The test will return variable results, depending upon which type apparatus is used. For most fluids woodworkers use, this probably should be a "Tag closed tester" which measures flash points that are typically pretty low... on the order of 140 F or less. Actually, if it is a well-made and thorough MSDS the type apparatus used will be stated. However, they often aren't so thorough. This is bad, because the measured flash point will vary depending on the type device used to measure it.

The temperature that a material will spontaneously burst into flame is defined as the "autoignition temperature" which is similar to the flash point in how it is done, but there is NO external ignition source provided. This is in my experience always somewhat higher temperature than the flash point. However, the point is moot. The key learning is that materials with a low flash point are more easily ignited than those with high flash point. The other learning is that if you measure the RATE that temperature rises in those oily rags, for example, you will find that as time goes by the temperature climbs ever faster until it ignites. This means that there may be only a very short time between the time an oily rag reaches the flash point of the (let's say linseed oil) and the time it gets to the autoignition temperature. Also the more quantity of (linseed oil) you have the faster the rags will get to the burn point. But a very good blog point.

Sam Whitley
Analytical Chemist