Smoke is not the only problem you will face when there is a fire in your home or your office. Soot is also a byproduct of such events, and is equally dangerous to a person’s health as the smoke lingers after a fire. The ash that is produced after a fire can also carry with it toxic substances that can irritate your skin, your eyes, and if inhaled, can cause respiratory and nasal problems. Some soot may even have cancer-inducing chemicals in them.

Smoke damage can affect a home or business structure in unexpected ways. When faced with the aftermath of a fire, home and business owners may find the location and concentration of smoke and soot residue perplexing and astonishing. Policy holders often find residue in the strangest of places and may question their insurance agent or adjuster as to why the smoke and soot settled where it did.

Smoke & Temperature
Because hot air rises, the temperature of smoke lifts it upward. Smoke typically climbs until blocked by a ceiling or overhang. In the absence of strong opposing air currents, the greatest concentrations of smoke exist immediately above the fire area. Since colder air sinks below warmer air, the heated air (and smoke) tends to migrate to colder surfaces, such as outside walls and windows. As air mass is cooled by the immediate area of an outside wall, it drops and follows the contour of the wall. This initiates convection currents, which bring more warm air to the cooler surface to replace the air that has dropped due to the temperature gradient. Because of this dynamic and flowing air current, smoke will migrate toward outside walls and windows and consequently deposit more residue there.

Smoke & the Surrounding Environment Windows located on insulated walls offer a substantial temperature gradient and the convection currents may concentrate in that area. You may, therefore, find heavier deposits of smoke or soot residue on the back or lined portion of a drapery than on the surface facing the room. Venetian blinds and pull shades will show substantially greater smoke residue than the surrounding areas, making them good indicators of the overall extent of damage. Once smoke has left the immediate fire area, it will deposit on walls and ceilings in proportion to the size and composition of the smoke particles, the air velocity and the quantity of smoke residue produced. The temperature of the air and the gases accompanying the smoke will also promote migrations to unheated areas. Smoke will invasively penetrate seemingly enclosed spaces, such as closets, dresser drawers and wall cavities. The vapor pressure of gas increases with rising temperatures. This can be visualized as increasing molecular activity, or agitation, in warmer air. More rapid movement, plus the collision of molecules, makes the atmosphere molecularly “more crowded”. In cooler spaces, molecular movement is slower and therefore more space between particles exists. This represents an area of lower energy.

The heat-driven air of a fire has energy sufficient to carry smoke particles. There is a natural movement toward areas of lower energy, such as the cooler spaces of unheated closets, drawers, cabinets and wall cavities. Once in those spaces, the energy level is no longer sufficient to carry the particles aloft, thus they fall out of the air stream. This explains the puzzling tendency of heavy smoke deposits in enclosed spaces. Temperature gradients create air currents within home and business ductwork whether or not the blower is operating. The cavity above suspended ceilings may also serve as an air return and therefore receive greater deposits of smoke and residue than the finished ceiling beneath. These areas can also convey smoke residue to a wider area. Where forced air (e.g. HVAC systems) is present and operating, air return and surrounding areas frequently show greater concentrations of residue. If a hot water heating system is present, air convection currents follow the direction of heating mains and tubing and continue upward through openings cut for water pipes. This convection builds upward behind radiators and results in a smoke residue deposit visible on the wall above the unit. This explains the occasional wide distribution of soot residue following furnace malfunctions, which may resemble similar concentrations around the air registers of forced air systems.

Smoke & Particle Ionization
Smoke particles tend to be ionized in smoke detection equipment. This phenomenon explains several aspects of smoke behavior. Since opposite electrical charges attract each other and identical charges repel, smoke residue tends to demonstrate a degree of selectivity in its deposit pattern. Nail heads or Screw that are invisible beneath the drywall compound of a ceiling may be clearly outlined by smoke, since their magnetic attraction remains effective despite the covering. Smoke particles cluster here, just as metal filings align themselves and cluster on the head of a magnet. These nail head outlines are often referred to as “nail pops” when, in reality, the nail has not moved and the outline disappears as soon as the area is cleaned or painted. The combustion of some materials, particularly plastics, results in particles that carry a stronger charge than organic materials like wood, paper or cotton. In some cases, residues of this type (as well as soot from some furnace malfunctions) result in cobweb-like “smoke webs” that assemble in corners and at the junctions of walls and ceilings. In addition to plastics, this same characteristic of ionization (or polarity) is present in many synthetic fibers. Synthetic lampshades frequently attract noticeable concentrations of smoke residue while nearby silk or paper shade remains unaffected. Vinyl upholstery coverings tend to attract heavier concentrations of smoke and occasionally combine with smoke particles to form a permanent stain.

Smoke & Airflow pattern
Natural or man-made air currents carry and distribute smoke. Smoke and soot concentrations generally decrease in intensity as the distance from the fire source increases. However, ductwork and other connected cavities frequently provide a shortcut for smoke, carrying it to areas that otherwise would have received far less residue. As smoke travels from its source, it flows around obstructions within the air current that carries it. Each obstruction accumulates smoke (imagine water in a stream flowing around and past rocks) and act as a crude filter. Smoke concentrations are therefore found on the far side of door openings and the ceilings immediately above.

These concentrations decrease progressively as the distance from the fire source increases. Since air currents flow in smooth curves and bypass sharp angles and shallow cavities, corners formed by ceiling and wall junctions receive less smoke than adjacent areas. Surface obstructions can develop a shadow of residue. Closets receive surprising concentrations of smoke residue from the temperature gradient (being unheated) and because items inside readily collect smoke on irregular surfaces. The same process attracts smoke particles to drawer interiors and other enclosed areas. Smoke may pass through seemingly impermeable plastic. In these cases, expect more intense odor conditions.

Conclusion:
The location and concentration of smoke and soot residue after a fire can appear oddly random and inexplicable to home and business owners. When working with their insurance agent or adjuster and the restoration company called to the scene, policy holders may question how and why smoke and soot residues fell where they did. A general understanding of the physics and properties involved in this process can help take the mystery out of an already-stressful situation. Getting a company like Snag and Inspect a professional inspection company involved early helps ensure your interest are best served doing the insurance review.