Page 25 - Climate Control News Magazine Feb 2020
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Indoor Air Quality Feature
main airborne for longer if they are less than 5 microns in size. If an at- mosphere is dry, droplets breathed or coughed from an infected per- son rapidly shrink through evapo- ration, leaving more at 5 microns or less in size and capable of re- maining airborne for long periods.
Secondly, when viruses are con- tained in a tiny airborne hydrated droplet, the dissolved salts and proteins are harmful to the virus, rendering them inactive. In dry atmospheres, the droplets lose all their moisture from evaporation. The virus is preserved in a dry air- borne particle and remains infec- tious without the salt and protein solution to attack it. So dry air has the double-effect of causing more infectious droplets to remain air- borne and prolonging the infectiv- ity of the suspended floating air- borne viruses.
Beside the risk of promoting air- borne virus transmission, low hu- midity also directly impacts on the human body. Few of us need scien- tific evidence to believe that our skin is drier and cracks more in the winter than the summer. We feel and experience it for ourselves. However, there are still plenty of
scientific studies that have quantified the detri- mental effects, such as Sunwoo et al 2006.
Groups of young and old males were exposed to air at 10, 30 and 50%RH and were monitored for the effect on their skin, eyes and the func- tion of “mucociliary clearance”. This is the res- piratory system’s primary line of defence against airborne infection and involves mucous in the nose and throat capturing airborne pol- lutants and transporting them to the digestive system, where they are destroyed.
Sunwoo’s results showed that 20% less mois- ture was lost from the skin at 50%RH than at 10%RH, that people’s eyes were drier at lower hu- midity causing them to blink significantly more to compensate, and it took significantly longer for pollutants to be cleared from our nose in a dry room. Interestingly it also showed that peo- ple felt colder at lower humidity, indicating high- er room humidity could result in a 2°C reduction in the required room temperature.
Given that dry air promotes airborne viruses, the fact that it also detrimentally affects our body’s defence against them, is the most worry- ing of these effects of low humidity on the hu- man body. As it occurs inside our nose and throat, it is also the most unnoticeable.
Salah et al, 1998, specifically examined the effects of breathing dry air by depositing sac-
charin into subjects’ nostrils, while they breathed either dry or regular room air, and having them swallow every 30 seconds until they could taste it. When breathing dry air, the time it took the subjects to taste the saccharin increased by more than one third. Salah con- cluded that “breathing dry air results in exces- sive water loss by the nasal mucosa, which may in turn reduce nasal mucociliary clearance”.
So given that there is a lot of scientific evi- dence showing health is impaired when the hu- midity falls below 40%RH, why aren’t humidity levels in workplaces monitored and maintained in the same way temperature is?
The main reason is that unhealthy humidity levels are not easily perceivable. The human body can sense a cold room but it cannot rec- ognise a dangerously low humidity. It is not unusual in Australia for indoor humidity lev- els in hospitals and offices to drop below 40%RH in the winter due to heating, or in the summer due to air conditioning. However, people tend not to associate the increased lev- els of flu and colds they experience in these seasons to a dry indoor atmosphere.
Maintaining an indoor humidity with hu- midification systems is relatively easy to do.
“MAINTAINING AN INDOOR HUMIDITY WITH HUMIDIFICATION SYSTEMS IS RELATIVELY EASY TO DO.”
– IAN EITZEN, BUSINESS DEVELOPMENT MANAGER, CONDAIR AUSTRALIA.
Breathing dry air impairs our body’s natural defence against airborne pollutants. Caption: Breathing dry air impairs our body’s natural defence against airborne pollutants.
There are many options for any type of build- ing, no matter how big or small and the cost is comparable, if not less, than that for tempera- ture control systems. Employers accept the need to provide heating in the winter and cooling in the summer for the health and pro- ductivity of employees but humidity control is nearly always ignored.
In 2018, there were 125 deaths in Australia confirmed as being due to flu, and around 60,000 cases. In 2017, there were 1,163 deaths and quarter of a million cases . Airborne infec- tions, such as flu, have a highly detrimental impact on Australian society, and cause a sub- stantial drop in productivity due to absentee- ism. There can be no doubt that airborne cross infection at the workplace presents a clear risk to health and welfare.
As the science all points to a healthy indoor humidity being 40-60%RH, the legal and mor- al obligation on employers to provide a healthy workplace should extend to managing indoor humidity levels throughout the year. ✺
Dry air promotes airborne viruses and inhibits our defences against them.
CLIMATE CONTROL NEWS
FEBRUARY 2020
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