Odor control is a marriage of science and art. When the proper techniques are followed, the restoration technician can create a more pleasant and often more healthful environment.

Let’s begin with the most widely accepted definition: An odor is a gas that people notice. Whether an odor is pleasant or unpleasant is very subjective. The odors a particular individual likes or dislikes are largely dependent on that person’s age, body chemistry, personal experiences and cultural background.

In addition, an individual’s ability to smell varies greatly. Women typically have a greater ability to detect odors than men. Younger people have greater olfactory sensitivity than we mature people. Smokers have a reduced ability to smell compared to nonsmokers. In addition, our sense of smell and taste are linked. If we have a sinus infection, food may not taste the same as when we are well. Head trauma and exposure to certain chemicals may also affect our ability to smell.

Preliminary Challenges

Bearing these factors in mind, I approach an odor contamination problem as a four-part challenge.

First, identify the source or sources of the odor. Remember that odors are gasses. These gasses are being released from somewhere: can I identify those sources by asking the building occupants, and yes, by my own sense of smell?

Second, I deal with the gasses that are in the air by capturing or changing them so they are no longer objectionable to the occupants.

I call the third challenge the “secondary deposit.” As odors travel through a built environment, they may be “adsorbed” into various materials. Adsorption is the process of a material accepting and retaining an odor on its surface. Typically, the more porous a material, the more likely it is to adsorb odors. Some odor control professionals call these surfaces natural wicks. Materials such as fabrics, unfinished wood or matte finish paints tend to accept odors, only to release them, or off-gas, at a later time. Off-gassing is even more likely to occur when the temperature of the materials is increased. In my experience, odor control professionals often neglect to treat these secondary deposits of odors. The failure to do so leads to unsuccessful odor control and frustration for themselves and their customers.

Using heat and steam is a simple but effective way to test if surfaces are retaining an objectionable odor. Apply warm water via trigger sprayer on various surfaces and then apply heat with a hair dryer or heat gun to the wetted surface. The heat and evaporating water will open the pores in the material and stimulate the release of the trapped gasses or odors. This process can be helpful in identifying the exact location of contaminated surfaces and materials.

Strong adsorbents like baking soda and activated charcoal or carbon can be used to tackle these types of odors. Activated carbon has been cleaned with heat and steam to remove contaminants from its adsorption sites.

The fourth and perhaps most difficult challenge is the odor in the client’s mind. Sometimes these odors are called psychological or heightened awareness odors. They most commonly occur when the client has suffered a traumatic event such as a structural fire or the death of a family member or friend. To be successful with this type of odor, the contractor must be able to communicate effectively with the client. In many cases, including the client in the deodorization process by explaining the process as work is completed can prevent the perception of odor.

Contractors can also leave behind an odor counteractant. I often ask clients to choose which of a selection of counteractant scents they feel “smells clean” and then leave that particular fragrance behind to provide a lingering effect. What smells clean will vary from person to person and from culture to culture. At the present time, many in North American seem to feel citrus or orange fragrances smell clean. In truth, clean has no odor.

Removing Odors

On the practical side, those who choose to work in the odor control field follow four general principles.

First, remove as much of the source of the odor as possible. While that’s common sense in most situations, there are times when source removal is impossible. Odors in health care facilities, animal lovers with problem pets or external sources of odors such as a waste treatment plant can be very difficult for the odor control specialist.

Cleaning the source area is the second principle of odor control. Cleaning may remove more of the source of the odor. During the cleaning process, use a commercial product to reduce or change the objectionable odor that is being released from the primary odor source. Most commercially available “deodorizing” products combine masking and pairing agents. Masking agents tend to overwhelm or cover an objectionable odor with one that most people will find more pleasant. The problem with using a masking agent alone is that if the product evaporates faster than the objectionable gas, the client is likely to smell the old odor again.

Pairing agents work differently. At the molecular level, the product combines with and changes the objectionable odor. Pairing agents are not normally used alone because each type of odor requires specific pairing agents and it is not practical to pair every type of odor that may be present. Even in situations like a structural fire, different materials may be consumed during a fire, in different quantities and at varied temperatures. These differences are so numerous that most manufactured products may start with pairing agents but masking agents must also be utilized for effective odor removal.

The third factor involves the extent to which the odor has penetrated structural and content materials. To truly deodorize porous surfaces, one method is to allow or cause the temperature of the structure to rise. Warmer temperatures will again open the pores in the material and stimulate the release of the objectionable odors. Once airborne, the odors can be ventilated to the outdoor environment or captured with an air filtration device with an activated carbon filter.

The last general odor control principle is sealing. Commercial sealers are designed to coat surfaces with an impenetrable barrier so any odors that remain in the materials do not become airborne and irritate the building’s occupants. When evaluating a product for this purpose, ask for the permeance rating. The lower the permeance rating, the more effective the product will be in slowing the release of the odor.

Sealers can fail for a number of reasons. Poorly prepared surfaces or sealers applied at the wrong temperature may result in sealer failure. Over time, the building may shift, causing the material to bend or twist and break the seal. Repairs, remodels or even cleaning can also disrupt the seal, resulting in odor control failure.

Besides the adsorbents pairing and masking agents described above, there are other methods to attack or eliminate odors. One of the most common is to use an oxidizer such as hydrogen peroxide, chlorine bleach, ozone and hydroxyl units oxidize or chemically “burn” the odor. This method of deodorization is permanent, and if properly applied, odors will not reappear. Oxidizing is especially effective on organic material, such as skunk and other animal sources, trauma scene situations and naturally fueled fires.

Bio-enzymatic products utilize beneficial bacteria to consume organic material and control the associated odors. This type of product is useful for cleaning residue from surfaces in protein-fueled fires, sewage losses or trauma scene situations. Bio-enzymatic products can also be used successfully to treat soil in crawl spaces that may have been contaminated with fuel oil or sewage.

 As you can see, the causes and treatments of odor control situations vary widely. To be successful, professional odor control contractors must be familiar with all of the methods available to them. I would encourage every contractor to take an odor control class to achieve consistent odor control success.