Is The Relative Humidity (RH) In Your Office Making You Sick?

Sper Scientific Indoor Air Quality

Sper Scientific 800048 Indoor Air Quality Monitor

During the cold winter months, buildings are closed up tighter with less outside air being introduced into the buildings, resulting in an increase in various indoor air pollutants. While such a scenario may have some validity in homes and buildings that do not have mechanical ventilation, the same cannot be said for all buildings.

An Indoor Air Quality expert in the New York area collected and analyzed the air quality data from over 125 different “Class A” commercial buildings located in the Metropolitan New York region over a five year span. For most of these buildings, air quality testing was performed two to four times a year for many common parameters including carbon monoxide (CO), carbon dioxide (CO2), total volatile organic compounds (TVOC’s), temperature and relative humidity (RH). In analyzing the extensive amount of data gathered, more than 18,000 readings for some of the parameters, various averages and trends were computed.

When the data collected in the spring and summer months was compared to that which was collected in the fall and winter months, a number of somewhat surprising discoveries were made. As can be seen in the table below, there was virtually no difference between the average spring/summer and fall/winter concentrations for most of the parameters which were tested for.

Parameter Spring/Summer Fall/Winter Applicable Guideline Limit
CO2 614.5 ppm 619.1 ppm 700 ppm above outdoor levels
CO 1.45 ppm 1.72 ppm 9 ppm
TVOC’s 1.25 mg/m3 1.21 mg/m3
Temp. 73.9 F 74.3 F 74-78 F summer/68-75 F winter

A significant difference in indoor RH levels with regards to the seasons was noticed. In the spring and summer months, RH levels were found to average nearly 42 percent. In the fall and winter months, though, RH levels averaged under 29 percent, with over half of all the readings below 30 percent and levels as low as 9 percent recorded in some buildings. Low RH levels have been reported to increase the incidence of upper respiratory infections (i.e., common colds) and to cause dryness and irritation of the skin. Other symptoms include dry and sore nose and throat, bleeding nose, sinus and tracheal irritation, dry scratchy eyes and inability to wear contact lenses.

Humidifiers can help to alleviate the symptoms resulting from low humidity, although they are rarely recommend if the problem is purely a comfort issue. Humidifiers, if they are not well maintained and the water changed frequently, can present a serious health risk to building occupants. Excess moisture levels, if left unchecked, can result in microbial growth on building materials. In addition, bacteria can proliferate in a humidifier’s water reservoir, resulting in endotoxins, which are present in the outer membrane of the cell wall of Gram-negative bacteria, being introduced into the indoor air. Exposure to low levels of these toxins can cause airway inflammation and cough, while acute exposures to high levels can result in flu-like symptoms. So when you hear that people “have been getting sick more often than usual”, realize that the problem is more likely than not due to low indoor relative humidity levels. Do not, however, automatically assume this is the problem. It is always best to properly monitor the levels of RH in the workplace and make proper decisions based on the results of these measurements.

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