One of the most important aspects of fire investigation is determining the potential for a suspected ignition source to actually ignite a given fuel. Sometimes the determination is not complicated.
For instance, most people involved in fire investigation know that a small electrical arc produces sufficient energy to ignite natural gas or propane that is mixed in the proper proportions with air. However, would that same electrical arc produce sufficient energy to ignite a solid wood two-by-four stud commonly found in wall construction? The answer is most probably not.
Electrical arcs can produce temperatures that are in the range of several thousand degrees. Many reference texts provide temperatures in the range of 450 to 800 degrees Fahrenheit for the ignition of wood to occur.
Temperature however is not the only factor in determining the competency of an ignition source. The temperature of the ignition source must be maintained for a long enough period in order to raise the temperature of the fuel to its ignition temperature. In other words, the ignition source must produce or have enough stored energy to generate and maintain those necessary temperatures until ignition is achieved. In most cases, electrical arcs are very brief and do not generate the energy necessary to ignite structural lumber such as a two-by-four wall stud.
Think about a candle. The temperatures in a candle flame can easily exceed 1800 Fahrenheit. If you were to hold a solid block of wood in that candle flame, it would take time for it to ignite. This is because sufficient heat must be transferred into the wood in order to raise its surface temperature to its ignition point.
Now think of a common wooden match. Again, the flame of a match produces temperatures well in excess of what is necessary to ignite wood. Do you think you could hold a single match in your hand long enough to ignite a solid wood two-by-four? Do not try it! The two-by-four likely will not ignite before the match burns out and you will probably be burned trying to hold the match.
In future e-zines we will look at some of the other factors involved in determining ignition source competency.