What factor could increase the fire load at a construction site?

The accumulation of construction debris is a factor that can significantly increase the fire load at a construction site. Fire load refers to the total amount of combustible materials present in a given area, which influences the potential fire intensity and duration. Construction debris, such as wood scraps, packaging materials, insulation, and other discarded flammable items, can create a hazardous environment by providing ample fuel for a fire.

In construction settings, workers may often leave materials lying around, especially if they are not managed properly. This neglect can lead to a higher concentration of combustibles that can ignite easily, especially in the presence of heat sources or sparks commonly found at job sites.

Other options, while they relate to fire safety, do not contribute positively to the fire load. Low humidity levels can affect fire behavior but do not intrinsically increase the amount of combustible materials. The use of painted surfaces usually refers to coatings that may not significantly change the underlying materials' combustibility. Installation of fire extinguishers is a proactive safety measure intended to mitigate fire risks rather than increase fire load. Thus, it is clear how the accumulation of construction debris directly correlates with an increased fire load, making it the correct choice.