Some signs of poor air quality, such as smoke and leaking gas, are easy to detect with a basic sniff test. Others, such as carbon dioxide, evade human senses so well that they're impossible to control without advanced monitoring hardware. Although most people know that substances like volatile organic compounds, or VOCs, can cause sick building syndrome and other health problems, many of these gases can't be detected unaided.
Human Perception and VOCs
Unfortunately, there's no universal rule when it comes to VOC odour. Some organic chemicals, such as the ethylene glycol (1) found in antifreeze and industrial chemicals, have absolutely no odor or color. Although this chemical's taste has been described as sweet, ingesting it would be an ill-advised testing strategy because it's highly poisonous.
Other things that produce VOC emissions are associated with odors that aren't always consistent. For instance, building materials such as paints and varnishes release overpowering fumes when they're still curing, but some of these odors come from non-VOC chemical ingredients. Activities (2) like smoking, burning wood and sawing certain wood composite building materials all produce characteristic smells that are often independent of their VOC contents. With many products, such as air fresheners and cosmetics, artificial scents might overwhelm or mask any detectable VOC smells.
VOCs That Smell
A few VOCs stand out for their strong odors. Many also cause physical irritation, such as burning respiratory tracts, asthma symptoms and other health problems that might make it wise to install a smart IAQ monitor.
Formaldehyde, which occurs naturally, can be extremely dangerous when inhaled at high concentrations. This carcinogenic substance is a major indoor air quality, or IAQ, problem in several homes due to its once-widespread use as a chemical ingredient in building materials including foam insulation, floor finishes, paints, varnishes and particle board. Many individuals can smell formaldehyde at concentrations as low as 0.3 parts per million, or ppm, and people may experience burning eyes or other forms of sensory irritation at around 0.5 ppm.
It's worth noting that these levels are significantly higher than what's considered safe: The U.S. Environmental Protection Agency, or EPA, limits formaldehyde IAQ concentration levels to 0.016 ppm.
Also known as dichloromethane, or DCM, this common solvent emits a characteristic sweet scent. Like formaldehyde, it poses relatively low risks in certain forms, but it's extremely volatile, so it's easy to inhale.
Individuals who suffer DCM inhalation overexposure can experience eye and respiratory tract irritation, nausea, dizziness and weakness. Too much can be fatal, and since the body breaks it down into carbon monoxide, dichloromethane can result in poisoning. DCM is a common ingredient of paint strippers and some hobby adhesives.
Other Strong-smelling Chemicals
Ethylbenzene (3), which one PubMed study found to be at significantly higher concentrations in areas with benzene-contaminated groundwater, is known as one of the five VOCs (4) that create "new car" smell. Since it can break down into other odorless compounds in just three days, however, its gasoline-like odour isn't a reliable contamination indicator. Xylene, another sweet-smelling VOC commonly found in new cars and fossil fuels, has an odour detectable at around 0.08 ppm according to PubMed (5), but it can persist for months in certain conditions.
Ultimately, odour simply isn't a good way to detect VOC concentration levels. Although studies have shown that stronger smells in substances like tobacco smoke are linked to increased VOC risks (6), many hazardous chemicals don't smell at all.
Learning more and getting an air monitor is the best way to counter the hazards. Stay informed by reading up on these IAQ topics:
Are household carpets a VOC hazard? They do contain ethylene and out-gas other emissions.
Go beyond odour and get rid of volatile compounds at home
VOC exposure and concentration in Office Buildings