Charles C. Roberts

Halogen floodlights have been used in both residential and industrial applications for years. They are characterized by high light intensity on task and high heat dissipation.

Figure 1

Figure 1 is a drawing of a typical halogen light fixture. The fixture frame supports a receptacle for a cylindrical halogen bulb, which is protected from the weather by a lens and seal. The bulbs are very warm, and cooling fins are usually molded into the back of the fixture to help dissipate the heat. Most manufactures warn against placing these fixtures too close to combustible materials because of the obvious fire hazard, which leads us to the subject matter of this article.

Figure 2

Figure 2 is a large feed storage facility that was badly damaged by a fire that nearly consumed the roof. The arrow points to a fire origin at an eave in the vicinity of newly installed flood light fixtures. The fixture at the origin was badly damaged. Figure 3 is a view of another light fixture that had been installed in the storage area. There were no other ignition sources in the area, other than the electrical fixtures, since the building was not heated. The fixtures were mounted in an unusual way.

Figure 3

Figure 4

Figure 4 shows one of the unburned fixtures removed for inspection. A hole had been drilled in the back of the halogen flood lamp heat sink and a screw inserted to secure the fixture to the wood structure near the eaves.

Figure 5

Figure 5 shows the wood joist where the fixture had been mounted. The middle arrow is the screw hole while the two dark areas (left and right arrows) are parts of the heat sink that had pressed against the wood. The dark regions are advanced stages of pyrolysis: indicating that significant heating of the wood has occurred, drying it out, reducing ignition temperature and creating conditions for ignition. Inquiry as to the reason for the unusual mounting method of the lighting fixtures resulted in the following explanation. The lighting had been installed with proper clearance between the fixture and wood at a lower level on the wall by an electrical contractor. Several fixtures had been damaged by piles of feed that were being pushed up against the wall as shown in Figure 6. In order to eliminate the problem, the fixtures were moved by the facility’s maintenance people, to a location higher on the wall and secured using a wood screw in an attempt to make a sturdier fixture mount.

Figure 6

Figure 7

Figure 7 shows the back heat sink area of the fixture. Figure 8 is an infrared thermogram showing significant heating of the heat sink on the back of the fixture. The rear heat sink is the hottest surface on the fixture and was attached to a wood structural member using a wood screw. Apparently, one of the fixtures eventually ignited the wood joist and adjoining roof structure, resulting in the loss. It should be noted that pushing the feed up around the fixture as shown in Figure 6 aggravates this condition by reducing heat transfer from the fixture.

Figure 8

Most manufacturers of halogen flood lamps warn about the fire hazards of insufficient clearance between the fixture and combustible materials. Ignoring these recommendations can precipitate a significant fire loss as illustrated by this field expedient.