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AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
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BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
FAN NOISES, HVAC
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
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.
The page top photograph shows what is probably Aspergillus niger black mold spores, 2-4u in diameter, along with those lemon-shaped and nice looking Chaetomium sp. mold spores. More detailsand a close-up photograph of these particles are given just below.
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At left are large black ovate Stachybotrys chartarum mold spores and smaller Pen/Asp mold spores.
Aspergillus niger is often a toxic mold; Chaetomium sp. mold spores are likely to be at least allergenic.
What mold, house dust dust, allergen fragment, mite fecal, cat dander, or other airborne particle sizes are a concern for indoor air quality?
In the photograph shown here the large black Stachybotrys chartarum mold spores can be seen against our eyepiece micrometer which, after calibration, shows that these particular spores were about 7u x 15u in size.
The brownish tubular structures in our photograph are fungal hyphae. Another, smaller fungal spore is in the background. What's not addressed by some of the science in the air filtration and IAQ field is just what particle sizes are a worry. In general, larger particles, say 30u or 50u or long fibers, say 200u, are so big that they tend to be filtered in the nose of a human breathing that air. (1u here means 1 micron in size).
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.
Larger airborne particles, perhaps in the 20-50u size, which affect a person by carrying allergenic proteins or fungal mycotoxins into the body, might be still a concern (in un-filtered or otherwise contaminated building air) even though they get stuck in the nose or upper respiratory tract.
Some allergists have told us that they can tell by the nature of a patient's complaint what they're probably allergic to and what size and types of particles are in the patient's environment. When inhaled in a breath of air, these comparatively large fungal spores are more likely to be trapped in a person's nose.
If a patient has chronic rhinitus, for example, they may be responding to large mold spores like Alternaria sp. which may be as big as 15 x 50u. If a patient has lower respiratory complaints (pulmonary or in the lungs) they might be responding to very small mold spores like some of those in the Aspergillus sp. or Penicillium sp. size range, which we often see in our lab can be down in to the 1u range in size. The photograph shows some Alternaria sp. mold spores which are pretty big.
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.
Pollen grains (shown above) vary considerably in size but generally are bigger than many most many mold spores. Ragweed pollen might be about 20u in diameter.
Shown here are some stunning and still larger poppy pollen seeds collected outside of our forensic lab in Poughkeepsie, NY.
A guanine-containing dust mite fecal pellet and other insect fecals vary in size but some are pretty big, maybe 30 x 150u, much bigger than most mold spores, as are most pieces of dog or cat dander.
The photograph provided here shows both common dust mite fecal pellets and, in the same photo you can see much smaller and nice for comparison, some hyaline (colorless) Aspergillus sp. or perhaps Penicillium sp. mold spores which are in the one-micron size range.
Often when we examine an indoor dust sample in the microscope and when we look closely at mite or some other insect fecal pellets we observe that the pellets are comprised of mold spores that the insect has been eating. Usually those same mold spores are present in the dust sample.
But when the mold spores themselves are not seen in the sample, we know that mold was nearby, and our little insect assistants have provided us with the evidence of the presence of of indoor mold. Eating at least some kinds of mold spores apparently does not bother them one bit.
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
Bacteria - for an example see Legionella BACTERIA & HVAC Equipment - photo at left.
Nanomaterials - see NANOMATERIALS HAZARDS
Also see AIRBORNE PARTICLE ANALYSIS METHODS
And see our discussion of ultra-small particles
We provide a lot of information about finding, cleaning-up, testing, and preventing problem mold in buildings: see
Continue reading at INDOOR AIR QUALITY IMPROVEMENT GUIDE or select a topic from the More Reading links shown below.
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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.
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