Odors and Odor Thresholds  

Introduction
Odor threshold
Sources of odors
Minimizing complaints about odors

Introduction

It is not always possible to have an "odor-free" environment. Early on, it became apparent to building managers that no one can ventilate buildings with enough outside air to get rid of all odors. There are always going to be some type of odors; the key is keeping odors to a minimum and making sure they are appropriate for the setting. For example, it would not be good if an office smelled like a crowded locker room. However, odors are also very subjective. What may be pleasant to one person may be offensive to another; odors are rarely neutral. For example, people may wear perfumes and colognes to appear attractive to others. However, some may become physically sick from these scents.

The perception of odor is one of the most important factors triggering complaints about the indoor environment. If the air smells "stuffy" or unpleasant, the number of people upset with the quality of air in a building can range between 15 and 40% even with good ventilation rates and a high efficiency filter system. Sometimes the sensory systems of some people can cause them to imagine that they are being or have been exposed to a hazardous pollutant. This belief (psychogenic illness) can often trigger similar reactions in others and is most common in workplaces where there are odors and poor working relationships between workers and management.

Odor itself is not a good indication if something is hazardous. Some dangerous chemicals have no odor (carbon monoxide) or what some would consider a pleasant odor (vinyl chloride), while some safe substances may have a very offensive odor. Other substances may cause what is called "nasal fatigue." This is when your nose gets to the point when it can no longer smell the odor any more. The odor is not gone; you just cannot smell it.

Odor Threshold

For some chemicals odor thresholds have been determined. Though this will not tell you if a chemical is hazardous or not, it might give an indication of how much of a chemical is present. To get these limits, there is a panel of people with no nasal or sinus problems who indicate when they can first begin to smell a particular chemical. Then these numbers are averaged for the panel members to get the odor threshold. For example, ammonia, which has a very strong odor, has an odor threshold, of 17 ppm. The recommended exposure limit for ammonia is 25 ppm. Therefore, you may smell it before you reach a concentration that could be dangerous to you. However, you cannot always rely on odor. For example, carbon tetrachloride may cause cancer. It has a recommended exposure limit of 2 ppm but an odor threshold of 140 ppm to 584 ppm by the time you can smell it, you are way past what is considered safe. In addition, some things like carbon monoxide do not have an odor, so you cannot rely on that. Natural gas does not have an odor either though many utility companies add sulfur odorant to it so it can be detected before it reaches dangerous levels.

Sources of Odors

There are a countless number of things that can give off odors into the indoor environment. Some of them are: building materials, furnishings, carpeting, ventilation systems, and people. A few of the most common offenders include:

• Mold or mildew growth: this may give off musty odors, which are volatile organic compounds (VOCs) produced by the mold. The specific VOCs released are dependent on the type of mold and material it is growing on. Most microbially produced VOCs have very low odor thresholds. Smells are characterized as pungent, wet-damp, musty, mushroomy, or dirty. These microbial VOCs can be measured even though mold cannot be seen. Finding those mold specific VOCs is an indicator of mold growth..

• Odors from organic solvents: These could come from things like newly painted materials, furniture, vinyl or hardwood floors, and cleaners.

• An odor resembling that of rotten eggs: This could be sewer gas seeping into the building from a dry odor trap underneath the floor or sink and/or excessive negative pressure within the building allowing sewer gas to enter the building.

• Personal care products: Almost 15percent to 20 percent of North Americans have some breathing problems that are made worse by strong odors from scented products such as perfume or after-shaves. Strongly scented products can also trigger migraine headaches.¹

• New Materials: Furnishings and construction materials can have odors associated with formaldehyde and VOCs. Common products with odorous chemicals include:

• Odors can result from ozone and VOCs such as styrene and other aromatic hydrocarbons. Carbonless copy paper, transparencies, and labels result in additional odors.

Minimizing Complaints About Orders

• Choose materials that have no or low odor levels. Know that there is a difference between scent-free and unscented. Some industrial products that call themselves scent-free may have more VOCs in them in order to mask their naturally offensive smell than unscented products.¹

• Keep temperatures between 68°F and 78°F and humidity levels between 40  percent and 60 percent and use enough fresh air. Research shows that the higher the air temperature, the lower the acceptability of air quality and the more intense people perceive odors.²

• Keep things clean and throw out garbage.

• Do not use air fresheners or deodorizer products to mask other odors since they introduce additional VOCs and odors that may cause allergic and irritant reactions in susceptible populations.

• Keep materials and building clean and dry and prevent mold growth.

• Keep water in sink and floor traps.

• Air out new furnishings and materials before using them or bringing them into a home or building.

Because of some people's increased sensitivity to odors, some places are moving to become fragrance-free. For example, there are some women's concerts that set-aside a separate section that is designated as "chemical-free" so that those who are bothered by things such as personal fragrances and smoking can enjoy the show. Recognizing the health problems that scents can trigger for people who have asthma, allergies and environmental illness, the Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia implemented a "Scent-free" workplace policy in 1991. They ask their staff, as well as patients to not wear perfume, scented hairspray, cologne, scented deodorant, after-shave, or other scented products.¹

References

1. Marsh B. No scents is good sense. OHS Canada. Jan/Feb 1998;26-27.

2. Addressing the psychological aspects of indoor air quality by Professor Alan Hedge, Dept. Design and Environmental Analysis, Cornell Univ. Paper presented at the 1st Asian Indoor Air Quality Seminar in Urumqi, China, Sept. 22-23, 1996.