Black streaks in my Office: Mold or what?
I see black streaks radiating out from ceiling diffusers. The question asked is “Is this black mold?” Rarely is it black mold, but it’s not impossible. Black mold usually grows on damp paper such as the paper surface of sheetrock. It can grow outdoors on decomposed wood and be brought into the HVAC system. More often than not though, that black stuff is soot. In many cases, it is carbon from vehicle tires especially in metropolitan areas or where there is a large amount of vehicle traffic.
Soot is formed from the incomplete combustion of carbon-containing fuels. Although natural gas, wood fires, candles, and home heating oil are typical sources, soot can be formed during any combustion process. A recent research project which looked into this Black Soot Deposition (BSD) phenomenon revealed that candles are a common (but not the only) source of BSD. Soot can also be from diesel (truck) engines. Thus, in cities and towns, the diesel soot is likely to appear on the diffuser bringing outside air into the office. Soot can also come from cigarettes, pipes, and cigars.
Soot particles are extremely small, usually less than a micron in diameter (a micron is 4.4 millionths of an inch). They are so small that they easily pass through air-conditioning filters but are too small to be seen until they accumulate. Soot particles tend to deposit on cool surfaces such as walls, floor carpeting, and air supply vents, which are precisely where they are seen. They also deposit on electronically charged surfaces like computer screens and plastic Venetian blind slats. Also, because soot particles are so small, they can penetrate to the alveoli, the deepest parts of the lungs, where gas exchange occurs.
If a soot problem exists, testing the office air quality and inspection of the HVAC system by an Indoor Air Quality Expert is the proper first step. Laboratory analysis by optical microscope or the more precise SEM (Scanning Electron Microscope) is necessary to define what the black particles are—mold or soot.