"Testing of Solder, Wood and Insulation to Determine Combustibility"
One of the more interesting cases that we have dealt with involved a house fire allegedly caused by the soldering of copper refrigerant lines. In this particular case, the owners of the house were having an addition built onto their existing residential structure. In the process, the condenser half of the air conditioning unit was relocated to the opposite side of the existing house. By doing so, the refrigerant lines also had to be rerouted through the attic to be reconnected with the air handler section. In order to make the connections, additional copper tubing was needed so as to lengthen the existing lines. The old and new lines were then soldered together using a propane torch and silver solder. In a soldering operation, the copper lines are heated with the propane torch until the copper becomes hot enough to melt the solder on contact with the copper. After completing the soldering operation, approximately nine hours passed between the completion of the work and the notice of the fire. After the fire occurred, attention was focused on the work that was done by the HVAC technicians.
In order to determine whether the soldering operation could have been responsible for causing the fire, models of the ceiling were constructed and filled with different types of insulation as shown in figures 1 - 3. Drops of silver solder were then melted and
Figure 1 Ceiling model filled with fiberglass insulation
Figure 2 Ceiling model filled with cellulose insulation
Figure 3 Ceiling model filled with mineral wool insulation
allowed to fall onto the insulation and wood. The temperature of the insulation was also monitored in order to track whatever rise in temperature occurred. As the solder droplets fell on the insulation, the insulation in each case, blackened and emitted smoke but did not ignite. Moreover, the solder cooled so quickly that any temperature rise was not enough to sustain ignition of the wood. The typical condition of the insulation and the wood is shown in figures 4 and 5.
Figure 4 Condition of nsulation and wood after contact with molten solder
After demonstrating that the solder was not going to cause of ignition of any of the ceiling materials, the same rationale was applied to the electrical wiring. In other words, would the solder melt the wire insulation and cause a high resistance short circuit to occur that would generate enough heat to sustain combustion? After several attempts to melt the insulation, the exterior jacket was never fully penetrated and the interior jackets surrounding the conductors were never damaged. The condition of the wire is shown in figures 6 through 8.
Figure 5 Burn spot on attic side of ceiling created by solder - no ignition of paper covering of sheet rock
Figure 6 Exterior insulation jacket never penetrated by molten solder
Figure 7 Additional burning of exterior jacket with solder - no penetration
Figure 8 No damage sustained by the interior insulation jackets surrounding the copper conductors
