Cornell University Ergonomics Web

DEA3500: Ambient Environment: Ventilation Basics


Indoor Air Pollutants

"Particles or gases that occur in the air inside buildings that adversely affect the health of their occupants"(Hinkle, 1981)

Acceptable Indoor Air Quality

"Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction"(ASHRAE, 62-1989)

Anatomy of system (slides)

Fungi (molds)

Up to 200,000 species, at least 45 species known to cause illness.Fungi are plants and range from single cell organisms e.g. yeast to multicellular forms. Multicellular fungi have a body mass (mycelium) plus turbular filaments called hyphae.

4 main groups: (depends on how they reproduce)

  1. Phycomycetes - Rhizopors (black brad mold)
  2. Ascomycetes - Pencillium, yeast
  3. Basidiomycetes - Mushrooms
  4. Fungi imperfecti - Aspergillus, penicillium (some species)

Fungi can survive wide climate ranges
Temperature = -10C to 65C
RH = >75% (c.f. bacteria which need RH>91%)

Up to 30% population show allergic reactions to fungal spores -- itchy eyes, sneezing, coughing, wheezing, shortness of breath. Can become sensitized to fungi, after one large exposure can get reactions to very low exposures. Some fungi (Aspergillus flavies; Stachybotrys atra) produce toxic metabolites which are volatile chemicals known as mycotoxins which also can cause kidney and liver damage.

Jaakola et al. (1990)

Looked at 893 workers (439 men, 454 women) in 8 storey office building in Helsinki. Data collected using 12 month self-administered questionnaires on frequency of colds.

Results analyzed using logistic regression and results expressed as an odds ratio

Odds Ratio


    YES NO

odds ratio = AD / BC i.e. (Yes/Yes) x (No/No) / (No/Yes) x (Yes/No)

Microbiological Hazards - Bioaerosols

Human skin is main source of many indoor air bacteria!

2 major types of problems:

Hypersensitivity pneumonitis & humidifier fever

(similar to farmer's lung, sewage sludge disease, and pigeon fancier's disease).

In 1950's studies established a relationship between malaise, cough, shortness of breath and contaminated humidifiers, whether these are personal humidifiers or in air conditioning systems.

Bacterial contamination of humidifier systems in hospitals has been associated with post-operative wound infections.

Effects of contamination greatest in places where there is organic dust available to contaminate humidifier e.g. wood, paper, and textiles.

Illness occurs when worker returns to work after a period away from work and symptoms are those of an influenza-like illness with general malaise, cough, shortness of breath, etc. Sometimes called "Monday sickness"! Disease predominates in winter months and after air conditioning shut down.

HF is thought to be an allergic response to allergans--viable cells, spores, dead cellular material (proteins, polysaccharides).

Dead cellular material are typically less than 0.5µm and therefore capable of deep lung penetration.

Type of organisms which develop in humidifiers depend on: - nutrient content of water - pH of water - temperature of water

Also initial microbial colonies may produce waste products which become the nutrients for other organisms, which may result in a growth chain--a succession of organisms: [bacteria >> fungi >> algae>> amoebae]

Contaminated humidifiers typically will have surface slime on sides.

Asthma - may be provoked both indoors and outdoors by house dust, animal proteins, fungal spores, pollens, molds etc. E.g. house dust mite (Dermatophagoides farinae (US) and Dermatophagoides pteronyssinus) that live in mattresses, furniture stuffing, etc. Numbers increase with increased humidity and increased temperature.


An ounce of house dust can contain 42,000 mites Each year 43 million tons of dust settle over USA: 31 million tons are natural, 12 million tons are man-made. Each body sheds about 50 million skin scales per day. Virtually every house contains dust mites. 10-15% of people have allergy to dust mites, 80% of these are allergic to feces, 20% are allergic to proteins in parts of the mite. Membrane covers the mite feces pellet and it is so strong that after 16 hours in salt water it doesn't break down. The allergy-causing potential remains for months! Mite counts normally highest in bedrooms where there is the highest dead skin counts. Each mattress contains 1-2 million mites. Each m2 material contains 1000-10,000 mites.

Mites cannot survive at humidities below 50%. Home heating of 70 degrees F and 50%RH or less will control mites. At 80 degrees F, RH has to be 40% to prevent mite growth. Therefore cool homes have fewer problems than warmer homes. Mite colonies hit low points in winter but are worse in spring, summer, and fall times.


Most fungi found outdoors Pasanen et al (1990), Finland, - Fungi will grow on damp surfaces e.g. ceiling tiles - ceiling tile

Brunekreet et al (1990), Netherlands, - fungi found in carpets, furniture, upholstery, wallpaper, etc. In HVAC systems fungi can grow in ductwork, on diffusers, - ventilation diffuser, on surfaces of cooling coils, in humidifiers, in condensate trays, in filters, etc. In spring and summer, highest number of outdoor fungal spores c.f. summer and winter, but not necessarily true for indoors.

Preventive measures

Viral illness

Respiratory tract infections (mainly viral illnesses) account for

Relationship between spatial design of buildings and risk of respiratory tract infections is poorly understood. Some evidence now suggests an important role of spatial layout and environmental services.

Brundage et al. (1988)

Compared 4 army training centers over a 47 month period (1982-86) and recorded incidence rates of febrile acute respiratory disease (ARD). Comparisons were made between rates among basic trainees in modern air-conditioned barracks and those in old barracks with operable windows and mechanical extract only (natural ventilation). HVAC barracks recirculated 95% air, natural barracks recirculated 50% air. Results show increased risk of ARDs in HVAC barracks.

Microbial coatings as a preventive measure

Spray all interior surfaces of airhandling system (including duct work) with an anti-microbial compound (amphoteric amine neutralized organic phosphate). Recent surveys of 9 facilities before-and-after treatment shows significant benefits.

Rhodes & Gilyard (1990)


Legionnaires Disease - acute bacterial infection of Legionella pneumophila. First well-documented outbreak affected American Legion Conference in Philadelphia in 1976. Since 1978, over 60 outbreaks worldwide in hotels, hospitals, and offices. Disease is a form of severe pneumonia even though the bacterium is relatively commonplace. Characteristics of Legionnaire's disease:

  1. Bacterium grows in water, especially when this is around 35C, and bacterium multiplies rapidly at this temperature. (Because of this high temperature, the bacterium is not usually found in humidifiers but can be in cooling towers). It is thought to grow in amoebae in contaminated water. Bacteria is killed within 4 minutes at 60C and 8 minutes at 58C.
  2. Airborne transmission of infection.
  3. Plumbing (e.g. shower heads) and air conditioning systems (especially cooling towers) are involved in airborne delivery of bacterium.
  4. Bacterium is common in soil and some outbreaks also associated with soil excavations.
  5. Disease affects middle-aged and debilitated most seriously.
  6. 2 forms of disease - pneumonic (Philadelphia fever) and non-pneumonic (Pontiac fever). Pontiac fever may be another form of humidifier fever. Symptoms include malaise, headache, high fever, mental changes, and also gastro-intestinal symptoms and dry cough. If unchecked, leads to respiratory failure and death. Cooling towers major source of Legionella.

1988 - BBC - 96 affected by Legionnaire's disease: 3 dead (1 passerby)

Preventive measures

  1. Minimize storage of cold water and prevent stagnation - this is ideal for growth of Legionella.
  2. Keep hot water systems > 60C (140F). Most hot water systems designed to heat water to 49C - 120F to avoid scalding. Temperature at faucets should be 50C (120F) and thermostatically controlled faucets should be used to avoid scalding.
  3. Avoid aerosols - use closed-loop systems.
  4. Sterilize - chlorination kills bacterium. Also passing water through UV light can kill bacterium. (45 secs UV kills 97.4% bacteria.) Yamayoshi & Tatsumi (1990)

Actinomycetes - filamentous bacteria that resemble fungi in appearance. Heat-tolerant (grow at 55C) thermophilic actinomycetes e.g. thermoactinomyces candidus associated with farmer's lung. Optimum growth at 25C e.g. Streptomyces

Nevalainen et al. (1990) - studied 50 problem sites in homes, offices, schools, and day-care centers in Finland and sampled for bioaerosols. Controls were 107 sites (offices, homes, day-care centers). Results showed that

Streptomycetes - (a mesophilic actinomycetes) were present in 70% of samples from problem sites but in less than 10% of control sites. Streptomycetes also have an intense, "moldy" odor. More research needed on this because little is known about the health effects of mesophilic actinomycetes.

Respirable Particulates/Fibers

Asbestos - collective term for a variety of asbestiform materials which comprise thin, long fibers of certain minerals. Asbestos comprises 2 mineral groups: serpentine - chrysotile - layered tubes/fibers amphibole - crystalline structures 95% of asbestos use in USA is chrysotile.

Chrysotile (Greek - ("golden hair") - fibrous magnesium silicate. Fibers have higher tensile strength and are less acid resistant than other forms. Fibers are white and silky. Fibers are actually tubes of mineral. Estimated that 733,000 commercial buildings and 30,000 schools built prior to 1970 have asbestos in them. Asbestos is, or was, in a variety of products: ceiling tile, plaster, brake shoes, insulation, fire retardent, shingles, vinyl tiles, etc. Asbestos is only dangerous when fibers become airborne i.e. when product is cut, broken, drilled, sanded, abraded.

Friable asbestos is in applications such as when this was sprayed or troweled onto walls, ceilings, structural components of non-residential buildings as fire retardant or insulation around pipes.

Asbestosis  - inhalation of asbestos fibers leads to a type of pneumoconiosis (asbestosis) and mesothelioma (lung cancer). Fibers remain in lungs for many years and cause fibrosis--stiffening of lungs long after exposure. Cigarette smoking aggravates asbestosis.

STANDARDS (all based on fibers > 5 µ long)


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