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Industrial Hygienist Directory
ONE PERSON ADDS 37 MILLION BACTERIA TO A ROOM PER HOUR
Just one person in a room adds 37 million bacteria and
mold spores to the air every hour, according to a study published in
the journal Indoor
Most of the bacteria are stirred up from the floor,
where they were left behind by the room's prior occupants.
"We live in this microbial soup, and a big ingredient
is our own microorganisms," Jordan Peccia, associate professor of
environmental engineering at Yale and the principal investigator of
the study, said in a press release.
"Mostly people are re-suspending what's been deposited
before. The floor dust turns out to be the major source of the
bacteria that we breathe."
Not long ago research revealed what
lives in your belly button, so the overall amount of
bacteria is astounding.
This latest study is the first to quantify how much a lone human
presence affects the level of indoor biological
Peccia and his team measured and analyzed biological
particles in a single, ground floor university classroom over a period
of eight days: four days when the room was periodically occupied, and
four days when the room was continuously vacant. At all times the
windows and doors were kept closed.
The HVAC system
was operated at normal levels. Researchers sorted the particles by
The scientists found that "human occupancy was
associated with substantially increased airborne concentrations" of
bacteria and fungi of various sizes. Occupancy resulted in especially
large spikes for larger-sized fungal particles and medium-sized
The size of bacteria and fungi-bearing particles is
important, because size affects the degree to which they are likely to
be filtered from the air or linger and recirculate.
"Size is the master variable," Peccia said.
The scientists determined that about 18 percent of all
bacterial emissions in the room -- including both fresh and previously
deposited bacteria -- came from humans, as opposed to plants and other
Of the 15 most abundant varieties of bacteria
identified in the room studied, four are directly associated with
humans, including the most abundant, Propionibacterineae,
common on human skin.
Peccia said carpeted rooms appear to retain especially
high amounts of microorganisms, but noted that this does not
necessarily mean rugs and carpets should be removed. At least it's
good news that few of the microorganisms commonly found indoors are
infectious, he said, but added, "All those infectious diseases we get,
we get indoors."
Given that most Americans spend more than 90 percent of
their time inside, it's no wonder we're often sick. And it seems like
a vicious cycle, since we're inclined to spend more time indoors if we
do feel lousy.