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

pathogens In biology, a pathogen (, "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 germ. The term ...

and allergens 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 human pathogens as well as certain kinds of

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

and

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

Aerobiological engineering in healthcare facilities

Since

healthcare Health care, or healthcare, is the improvement or maintenance of health via the preventive healthcare, prevention, diagnosis, therapy, treatment, wikt:amelioration, amelioration or cure of disease, illness, injury, and other disability, physic ...

facilities can house a number of different types of

patient A patient is any recipient of health care services that are performed by Health professional, healthcare professionals. The patient is most often Disease, ill or Major trauma, injured and in need of therapy, treatment by a physician, nurse, op ...

s who potentially have weakened

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

s, aerobiological engineering is of significant importance to engineers of

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

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. Viruses are found in almo ...

, and other microbiological products such as endotoxins, mycotoxins, 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 (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...

s . Even large-sized droplets can remain suspended in the air for long periods if upward velocity of air in closed spaces exceed particle's downward velocity as dictated by their negligible mass. 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 buildings and Nonbuilding structure, structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also be ...

in hospitals dealing with

infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

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 *** Respirator, a ma ...

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 renders something unsuitable, unfit or harmful for the physical body, natural environment, workplace, etc. Types of contamination Within the scien ...

control.

Biocontamination in ventilation systems

Ventilation systems can contribute to the microbial loading of indoor environment by drawing in microbes 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 rooms. The American Society of Heating, Refrigerating and Air-Conditioning Engineers typically recommends 12-25 ACH in treatment and operating rooms and 4-6 ACH in intensive-care rooms. For rooms containing

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

patients, the

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...

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