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Guide to airborne & dust particle sizes: here we give a definition of Problem Particle Sizes & Types in Indoor Air, The definition of micron, common indoor air particle sizes in microns, and how they behave indoors.
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Definition of "Small" Airborne Particles & Their Hazards
Small airborne particles, say in the range of 5um (5 microns) and below are so tiny that they tend to be breathed more deeply into the lungs and might be more of a pulmonary (lung) health or IAQ concern for some building occupants. For purposes of discussing air pollution and health concerns around airborne particles, those particulates that are 2.5u and smaller are considered small and particularly dangerous. Certainly some air filters which capture large particles may nonetheless pass the smaller ones right on into the "conditioned" air.
New York Times has reported an increased concern among scientists who study the potential dangers of very small airborne particles. But the concern is not entirely new.
A 2012 study found that on days when concentrations of traffic pollutants were elevated the risk of stroke among humans increased by 30% and a separate study in 2006 reported a link between short-term exposure to air pollution and cardiovascular disease. The traffic-related air pollutants identified in the first studies included black carbon (BC), carbon monoxide (CO), NO2, ozone (O3), PM [particulate matter] smaller than 2.5um in aerodynamic diameter, and sulfur dioxide (SO2).
In 2012 the NY Times further reported on a study that reported:
Of interest, as we discuss in our review of How Air Filters Work, is the observation that very very small particles in the less-than-one-micron range are actually captured more easily by some air filter technologies than the 2.5u range small particles just named here or the larger 20-50u sized airborne particles named next.
Typical Stachybotrys chartarum "toxic black mold" spores that have received lots of media attention and public worry are a rather large warty, sticky mold spore (intended to be spread by cows walking through moldy straw) which is oval and is usually about 10 x 20u in size. Stachybotrys chartarum's still more irritating family member, Memnoniella echinata is a round black spore of about 10-12u in diameter.
Stachybotrys chartarum and Memnoniella echinata are not normally airborne mold spores, so if we find one or both of these in building air or in settled building dust or in the HVAC system, most likely a surface with that mold growing on it is or was nearby and it has been recently disturbed, say by demolition activity conducted without proper dust management.
Definition of a micron - how big is a micron?
How big is a one micron particle? How easily do such particles move throughout a building?:
Just as a few points of reference comparing particle sizes,
("u" or "um" here means micron or 1/1,000,000 of a meter or a millionth of a meter or about 1/25,400 ths of an inch if you prefer).
A one-micron Aspergillus sp. mold spore is so small that we find that they move in the air like a gas, right up from a moldy crawl space and through the building, and these particles tend to stay airborne much longer than their larger cousins. In absolutely still air (which never ever occurs inside a normal building), such a particle might remain airborne for more than 40 hours. Walking outside (where there is plenty of air movement and plenty of mold spores) a person is breathing in a few of these spores with each breath.
Fungal spores may be amplified indoors if there are problems with the heating or air conditioning systems
Breathing in a lot of some kinds of mold spores or other particles can be a problem wherever one is, but indoor allergens, toxic spores, or other irritants may be more of a problem indoors where they are not diluted by outdoor air, where some people spend lots of time, and where these problem particles are being picked up by a heating or air conditioning system, blown through the duct work, amplified in quantity by ductwork or air handler conditions, and then delivered personally to people in the living space.
Still Smaller Particles that May be Found in Indoor Environments
Frequently Asked Questions (FAQs) about the size of airborne or dust particles
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Question: Should I cover up mold in my basement - risk of contaminating HVAC system with mold?
I am currently looking into purchasing a home that has a leaking furnace and some mold in the basement because of a power outage causing a water pack up after a sump pump failure and subsequent backup. Most of the drywall with the mold was removed but there is still a little left (that I can see -- who know how much I can't). My original plan was to gut the basement, treat any and every surface down with an anti fungal wash, and let it dry out with a dehumidifier for a few months. After that was completed, I would replace the furnace and have the ducts cleaned. However, the FHA is requiring that I replace the missing drywall and furnace before they sign off in it.
Jay. it sounds as if you need to
Question: Clarify the size of fiberglass fragments and fibers
Great site - thank you so much. I'm confused about this statement:
AG thank you for pointing out my confusing statement, I will rewrite it for clarity. Meanwhile... What I meant to say is that damaged fiberglass can produce high levels of very small particles in the 1u range, (measured across the particle's longest axis) maybe even smaller, while normal, intact fiberglass insulation consists of much larger particles of great length, even though the diameters of some of those long, thus very large in length, may be thin in fiber diameter.
Questions & answers or comments about particles found in indoor air and dust - particle sizes
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