Many people believe it's impossible to remove all traces of smoke odor from a house damaged by fire, short of tearing the structure apart and replacing all materials. And it is true that heavy smoke odor cannot be successfully masked: sooner or later the pervasive smells will resurface if not treated properly. It is sometimes necessary to remove surfaces to gain access to smoke-contaminated structural members needing treatment or replacement. But in many circumstances smoke can be removed by less disruptive means-by using chemical treatments that counteract the odor-causing molecules at the source.

What's smoke odor? Consider for a moment what smoke odor is. What most people call smoke odor is actually a combination of smells produced by the interaction of chemicals during and after combustion. Many different materials burn during a building fire, including wood, fuels, plastics, fabrics, proteins, and countless others. All these materials produce different smells when they burn and as their charred remains "offgas" afterwards. Also contributing to the overall odor is the smell of fungi that flourish in areas soaked by water. Yet to the layperson, all the different smells add up to just "smoke odor."

Why is smoke odor so hard to treat? For one thing, it's difficult to reach. Smoke seeps through the minute cracks and crevices and leaves its residue on surfaces and in ductwork throughout a building. Sometimes the smoke also reaches structural elements such as framing members. To be effective, any chemical treatment must behave the same way, fully penetrating the building to find and counteract the odorcausing molecules.

Foggers and ozone generators. The three technologies that can do this are a wet fogger, a thermo fogger, and an ozone generator. Wet foggers and thermo foggers work on similar principles: Both break down odor-eliminating chemicals into microscopic particles, producing a "fog" that drafts through a structure, following the same paths as the smoke. These chemical compounds suppress the offgassing of any odor causing molecules they come in contact with.

The wet fogger operates by breaking a water-based chemical solution into an ultra-fine mist of particles several microns in size. Thermo foggers, on the other hand, pass the odor-eating chemicals through a heating element to vaporize them, creating a smokelike solvent- or oil-based fog much like the fog pumped out by trucks that spray for mosquitoes. (This fog is so smokelike, in fact, that we usually call the fire department before we use it, since people seeing the fog seeping from windows or vents often call to report a fire.)

When used properly, both foggers take advantage of a structure's natural airflow patterns, allowing the fog to penetrate to places where smoke has left its residue. However, each type of fogger tends to work best in different situations.

As might happen, for instance, in a fire that burned in only one room. Since wet foggers leave a residue, they are also useful in situations where a long-residual treatment is desirable, as in a building's HVAC ductwork. However, wet foggers don't seem to find their way through barriers and into recesses as well as thermo foggers do.

Thermo foggers, on the other hand, work well where the smell of smoke is less intense but more generalizedsuch as when a stove or electrical fire has spread smoke throughout a house. Here the thermo fogger's ability to penetrate barriers and find nooks and crannies more than compensates for its less concentrated impact. Its finer particles and lighter residue are other advantages that help make it the most widely used fogging technology.

The chemical formulas come in two versions: You can buy a general solution designed to attack all types of odors, or specific solutions targeted at smoke from specific materials, such as fuel oil, wood or protein. Solutions also can be bought to fight odors from pets, mildew, and other sources. Care must be taken to use the most appropriate treatment.

Ozone generators provide another alternative. They work by producing and distributing highly volatile O3 molecules that oxidize active odor-causing molecules in the structure and neutralize them. Extremely effective with most non-synthetic materials, they are also controversial. Ozone (one of the harmful emissions in car exhaust) is an EPA-controlled substance, with strict guidelines for its use-it should never be used, for instance, in an occupied home. Fortunately, its harmful effects fade rapidly, usually within a day. In addition to its polluting effect, however, ozone is believed by some to have an "aging" or fading effect on certain synthetics, such as those used in upholstery and carpets. For these and other reasons, many people shy away from using ozone generators.

Extra protection with sealing. If a finished surface or structural member is heavily contaminated with smoke, you can gain extra protection against odor by spraying or brushing on a sealer. This will further suppress offgassing and also help keep out moisture, that tends to bring out odors. Special sealers for this purpose are available in a variety of finishes, both clear and pigmented. The pigmented versions also can cover water or smoke stains. Sealer should be applied after cleaning and odor treatment, but before repainting or recovering with wallboard, flooring, or other finished surfaces.

Though not a cure-all, any of these technologies can be effective when used appropriately. Knowing when to use that one-or when other steps are called for-takes considerable knowledge and experience. You also need to know their limitations so you know when removal of wall or ceiling surfaces or even structural elements is necessary. But along with good old-fashioned cleaning, foggers and ozone generators often provide an alternative to dismantling an otherwise sound house. It rarely is necessary anymore to completely dismantle a sound structure to eliminate smoke odor.

Of course, the satisfaction of the property owner is the ultimate test. Restoration professionals should do whatever it takes to restore property so that the owners never will be able to see or smell evidence that the structure suffered from a fire.

Author: Lumpp, W.
Date/Pages: Jun 1990, 14, 24

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Article provided by the Association of Specialists in Cleaning and Restoration (ASCR).