HPAC Magazine
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Let’s Talk Stink

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December 19, 2017 by Robert Bean

indoor odour,olfactory senseOut of all the senses, the olfactory sense is one of the strongest for creating lasting impressions.i Odour memories also influence the way new smells are perceived. As a survival tool it serves as an early warning signal that something in the environment might be wrong. But smelling an odour does not define the exposure or risk for all occupants. When there is a bad smell, and the compounds are at concentrations that are not necessarily a health risk, the odour could be intense enough for some people to cause annoyance (a psychological experience) and/or irritation (a physical experience).
In higher concentrations; and for people who are sensitive to the odour; these experiences might manifest into feelings of general sickness. Symptoms ranging from nausea, vomiting, headaches, respiratory challenges, and disturbances of sleep to appetite loss, and irritation of the lungs, eyes, nose and throat may be experienced. Additionally, the perception of an odour, especially if it is sustained, may act as a prompt for some that either triggers stress-related illness or heightens awareness of underlying symptoms.ii
Odour perception is influenced by numerous factors, including genetic differences and ones state of health, culture, age and gender (consider the hypersensitive olfactory sense sometimes experienced during pregnancy). The degree that an odour becomes a nuisance is also a function of its location, frequency, intensity, duration, and offensiveness. Due to the numerous interactions and reactions, what a person judges as “smelly” must be treated as subjective and true for them, in the same way perceptions vary amongst people for other indoor environmental quality senses.
With regards to health effects, these depend on the type or combination of types of chemicals, the concentration(s), the length of exposure and whether the person is sensitive to the offending odour(s). Odour should not be the only factor used to determine health risks. Consider the life risk dangers of carbon monoxide and radon, which have no odour at any concentration. At the other end of the spectrum are sewer gas and mildew odours, which are perceptible but generally not life threatening.
The smelling sensation also carries with it a unique characteristic that happens when olfactory receptors become fatigued. Sustained exposure to offensive odours can result in olfactory adaptation leading to a decline of the unpleasantness over time.
North American demographics suggest building practitioners can expect an increasing number of people experiencing presbyosmia, which is a gradual decrease in the sense of smell that occurs with aging.iii Other disorders include anosmia, hyposmia, hyperosmia or dysosmia. Olfactory disorders are associated with head trauma, upper respiratory infections, nasal polyps, diseases such as Alzheimer’s, Parkinson’s and multiple sclerosis, certain medications, hormonal disturbances, drug abuse, dental problems, and toxic chemical exposure.iv
The number one rule in building science also applies to odours. What is in the outside wants in, and what is in the inside wants out.
The movements of energy and mass are triggered by differentials in pressure, temperature and moisture–and so it goes with odours. Think dispersion and diffusion. Biological or chemical based it does not matter. You get something wet it supports microbial growth and produces an odour which is transported with airflow (flow of mass). You heat something up (flow of energy) and it turns into particles and gasses, which have an odour and, again, are transported with airflow. The following is a partial list of odour sources in buildings:
Generated inside
• drain waste and vent pipes
• water systems (associated with fridges, dishwashers, washing machines, humidifiers, dehumidifiers, drinking water, grey- and black-water systems)
• stagnant and untreated water systems (condensate trays, evaporative type humidifiers)
• garbage and garbage disposal
• carpet, paint and surface coatings (interior and exterior)
• solvents, adhesives and cleaning chemicals
• furniture, fittings and finishes
• building materials
• pets and rodents
• poor personal and building hygiene
Generated outside
• environmental disasters such as fires and floods
• emissions from transportation and other combustion sources including those from neighbours.
• garbage/waste disposal sites
• industrial processing plants
• agricultural processing plants
• stagnant water sources (ponds, sloughs etc)
• pets and rodents
Metro Vancouver has a useful table for odours, identification and sources (see http://www.metrovancouver.org/services/Permits-regulations-enforcement/air-quality/factors/odour/Pages/default.aspx). Put it in your library for future reference.
In general for indoor odour prevention keep everything tight, cool and dry; except traps keep them wet. Maintain space humidity between 35 per cent and 55 per cent (+/-5 per cent). Use natural materials and finishes. Do not mask odours with air fresheners, candles or incense. These are bad products and only contribute to the poor state of air quality.
Maintain good personal and building hygiene. If things related to venting (plumbing, bathrooms and kitchens) become loose they will leak odours. If things are heated they too will stink. Avoid heating stuff up especially synthetics. If things get wet they will stink. Do not let things get wet–if they do get wet, dry them. Do not store chemicals, cleaning supplies and waste in living spaces nor in spaces connected to living spaces. If you must have pets, keep them groomed. Assign a place (outdoors if possible) for them to do their business and keep it clean.
The perimeters of buildings are places for animals and pests to hide, to stay warm/cool and find food and water. They also die near the perimeter. Animals and pests lead to odours. Do not make this area habitable. The first three to four feet around a home should be sloped, drained and look like the landscaping on the moon. I know this goes against the grain but it works. Outdoor air, if odour free, is good to bring in provided it is filtered. To get good outdoor air in you have to remove indoor air out. Ventilate but only if the outdoor air is odour free.
In general, for outdoor or neighbour odour prevention, live as far away from humanity as you can. Even agricultural land is not safe so go north into the bush and tundra.
If you cannot isolate yourself then seal up your home, condominium or apartment. Next to noise, smoking and cooking odours from neighbours generate the most complaints. Airflow is the transport mechanism. If air can travel from the offending source into the clean space it will do so via pressure, moisture and temperature differentials. Cracks, holes, elevator shafts and doorways are the pathways. The only way to stop it is seal up the spaces. If you cannot seal it up then it gets complicated and expensive.
There are a variety of adsorbents designed to take care of odours but these must be fitted into mechanical systems either as a standalone device or as part of the building system. They require power and regular maintenance and someone who knows about gases and adsorbents.
When the outdoor air is of poorer quality than the indoor air, do not ventilate – recirculate and filter. I know that goes against Codes but Codes are not logical when it comes to this matter. Your clients’ state of health and mind matter. Most poor outdoor conditions are temporary. Pick the time to ventilate either mechanically or naturally.
If you don’t like these options, did I mention the bush and tundra. Just don’t eat the yellow snow.v

Robert Bean is a Registered Engineering Technologist in building construction (ASET) and a Professional Licensee (Engineering) in HVAC (APEGA). He is president of Indoor Climate Consultants Inc. and director of www.healthyheating.com; a past ASHRAE Distinguished Lecturer; recipient of ASHRAE’s Lou Flagg Award and ASHRAE Distinguished Service Award; and a member of ASHRAE technical committees 2.1 (Physiology & Human Environment) 6.1 (hydronics), 6.5 (radiant), 7.04 (eXergy) and SSPC 55 (thermal comfort). Bean is also the author of numerous industry courses and seminars covering the building sciences, indoor environmental quality, energy, and radiant-based HVAC systems.
i Bell Labs, Odor Testing < http://bell-labs.com.au/odour-testing> accessed Nov. 2017
ii Dalton, P., Dilks, D.. 1997. Odor, Annoyance and Health Symptoms in a Residential Community Exposed To Industrial Odors, Preliminary Technical Report Submitted to South Camden Citizens in Action., Technical Report – TFEJ 01. Moneu Chemical Senses Center
iii Boesveldt S, Lindau ST, McClintock MK, Hummel T, Lundstrom JN. Gustatory and Olfactory Dysfunction in Older Adults: A National Probability Study. Rhinology. 2011 Aug. 49(3):324-30. (Medline].
iv Jeffrey E. Goldberg, MD. <http://www.jgoldbergmd.com/smell-disorders.php> accessed Nov. 2017
v Courtesy of Frank Zappa < https://youtu.be/TLIppgE45wM>.

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