Aerobiological engineering is the science of designing buildings and systems to control airborne

pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

and

allergens An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies. In technical ter ...

in indoor environments. The most-common environments include commercial buildings, residences and hospitals. This field of study is important because controlled indoor climates generally tend to favor the survival and transmission of

contagious Contagious may refer to: * Contagious disease Literature * Contagious (magazine), a marketing publication * ''Contagious'' (novel), a science fiction thriller novel by Scott Sigler Music Albums *''Contagious'' (Peggy Scott-Adams album), 1997 ...

human pathogens as well as certain kinds of

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

and

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

Aerobiological engineering in healthcare facilities

Since

healthcare Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health pro ...

facilities can house a number of different types of

patient A patient is any recipient of health care services that are performed by healthcare professionals. The patient is most often ill or injured and in need of treatment by a physician, nurse, optometrist, dentist, veterinarian, or other heal ...

s who potentially have weakened

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

s, aerobiological engineering is of significant importance to engineers of

hospital A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emergen ...

s. The aerobiology that concerns designers of hospitals includes

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

, and other

microbiological Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, pro ...

products such as

endotoxin Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer m ...

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...

s, and microbial volatile organic compounds (MVOC's). Bacteria and viruses, because of their small size, readily become airborne as bacterial

aerosol An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of anthropogen ...

s and can remain suspended in the air for hours. Because of this, adequate precautions and mitigation techniques need to be taken with

indoor air quality Indoor air quality (IAQ) is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort, and well-being of building occupants. Poor indoor air quality has been linked to sick building syndrome, reduce ...

in hospitals dealing with

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

Ventilation systems

At a minimum,

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Ventilator, a m ...

systems provide dilution and removal of airborne contaminants, which in general leads to improved indoor air quality and happier occupants. If filters are checked and replaced as needed, they can form an integral component of an immune building system designed to prevent the spread of diseases by airborne routes. They can also be used for pressurization of areas within buildings to provide

contamination Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...

control.

Biocontamination in ventilation systems

Ventilation systems can contribute to the microbial loading of indoor environment by drawing in

microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s from outdoor air and by creating conditions for growth. When microbes land on a wet filter that has been collecting dust, they have the perfect medium on which to grow, and if they grow through the filter they have the potential to be aerosolized and carried throughout the building via the

HVAC control system HVAC (Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. Usually a sensing device is used to compare the actual state (e.g. temperature) with a target s ...

Dilution rates

Bacteria in hospitals can be aerosolized when sick patients cough and sneeze and because of the large number of germs produced it is necessary that the number of air changes per hour (ACH) remain high in treatment and

operating room Operation or Operations may refer to: Arts, entertainment and media * ''Operation'' (game), a battery-operated board game that challenges dexterity * Operation (music), a term used in musical set theory * ''Operations'' (magazine), Multi-Ma ...

s. The

American Society of Heating, Refrigerating and Air-Conditioning Engineers The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE ) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration (HVAC&R) systems design and constructi ...

typically recommends 12-25 ACH in treatment and

operating rooms An operating theater (also known as an operating room (OR), operating suite, or operation suite) is a facility within a hospital where surgical operations are carried out in an aseptic environment. Historically, the term "operating theater" refe ...

and 4-6 ACH in

intensive-care Intensive care medicine, also called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes pro ...

rooms. For rooms containing

tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, ...

patients, the

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...

recommends an ACH of 6 to 12, with exhaust air being sent through high-efficiency-particulate-air (

HEPA HEPA (, high-efficiency particulate air) filter, also known as high-efficiency particulate absorbing filter and high-efficiency particulate arrestance filter, is an efficiency standard of air filters. Filters meeting the HEPA standard must ...

) filters before being sent outside.

Pressurized isolation rooms

In order to keep patients safe, hospitals use a range of technologies to combat airborne pathogens. Isolation rooms can be designed to feature positive or negative air-pressure flows. Positive-pressure rooms are used when there are patients who are extremely susceptible to disease, such as HIV patients. For these patients, it is paramount to prevent the ingress of any microorganisms, including common fungi and bacteria that may be harmless to healthy people. These systems filter the air before delivery with a HEPA filter and then pump it into the isolation room at high pressure, which forces air from the isolation room out into the hallway. In a negative-pressure system, the focus is on keeping infectious diseases isolated by controlling the airflow and directing harmful aerosols away from health care workers and other occupied areas. Negative pressure isolation rooms keep contaminants and pathogens from reaching external areas. The most common application of these rooms in the health industry today is for isolating tuberculosis patients. To do this, the air is exhausted from the room at a rate greater than that at which it is being delivered. This makes it difficult for airborne disease to go from a contaminated area to a hospital hallway, because air is constantly being drawn into the room rather than escaping from it.

Air sterilization processes

The normal means for filtration in healthcare facilities is low-efficiency air filters outside the air-handling unit followed by the HEPA (High Efficiency Particulate Air) filters placed after the air-handling unit. To be HEPA-certified, filters must remove particles of 0.3 μm diameter, with at least a 99.97-percent efficiency. Air burners sterilize air that is leaving contaminated isolation rooms by heating it to for six seconds.

Ultraviolet germicidal irradiation Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet ( ultraviolet C or UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA, leaving them unab ...

(UVGI) is another technique for special-purpose air sterilization. It is defined as electromagnetic radiation in the range of about 200 to 320 nm, that is used to destroy microorganisms. When HEPA filters are used in conjunction with UV sterilization tools, the results can be extremely effective. The filter will remove the bigger, hardier spores, and all that is left are the smaller microbes which are killed more efficiently by the high-intensity UV treatment.

References

* C.S. Cox ''The Aerobiological Pathway of Microorganisms''. Chichester G.B.: John Wiley & Sons 27, p. 118-119. * Godish, Thad. ''Indoor Environmental Quality''. Boca Raton, FL, USA: Lewis Publishers, 2001. p. 190. * Kowalski, Wladyslaw Jan. ''Aerobiological Engineering Handbook''. Blacklick, OH, USA: McGraw-Hill Professional Publishing, 2005. p. 6, 185, 231, 260, 528, 530. {{DEFAULTSORT:Aerobiological Engineering Biological engineering Ventilation Human habitats