The Indoor Environment

Indoor environments are artificially created ecological systems made up of a non-living or physical component and a living or biological one. Physical environments include structural, finishing and furnishing materials and their paints, coatings and sealants; various contents; and a climate measured by temperature, moisture and airflow. Living or biological environments typically include microorganisms, insects, plants, rodents, pets and humans.


Indoor ecosystems are smaller microenvironments or habitats that have their own physical and biological factors. These ecosystems also are pollutant reservoirs that may affect air quality components, such as interior and exterior wall cavities, ceilings, air-handling systems and crawlspaces. Others serve as reservoirs that readily collect particulates. These particulates include dusts, fibers, soil and debris that can harbor chemical and biological pollutants, like pesticides, lead residues and microbial insect and animal allergens. Textile floor coverings include upholstered and hard surface furnishings, bathroom surfaces and food preparation and pet areas.


Particulate in these reservoirs must be reduced through regular cleaning. If not, they can become indoor contamination sources through airborne dissemination caused by occupant activity and mechanical airflow. Such distribution can seed uncontaminated areas and degrade air quality. This exposes occupants and causes adverse health effects in susceptible individuals. Vulnerable individuals are at-risk in special environments that present significant cleaning challenges, including hospitals, schools, nursing homes and daycare centers. The general population often incurs health risks in high occupancy indoor environments, such as large office buildings, hotels and cruise ships. Everyone is at-risk in their home.


Cleaning manages unwanted matter. Effective cleaning:

  • includes practices and procedures that maximize pollutant removal;
  • maintains and preserves the integrity of treated surfaces or materials; and
  • depends on efficient cleaning equipment and products.

Special Environments

Special environments harbor those who are susceptible to the negative health effects of indoor contaminants and pollutants. These environments include schools, healthcare facilities (e.g., hospitals, rehabilitation centers and nursing homes), daycare centers and homes. They are populated by individuals with severe allergies and hypersensitivities, like asthma, and those with suppressed or deficient immune systems. This makes them susceptible to life-threatening infections caused by indoor contaminants, such as environmental molds.


Children have immature immune and organ systems. This puts them at risk during their growth and development, especially from metals and chemical residues present in household dust. The elderly also are at risk with their waning immune systems and susceptibility to respiratory viruses. They often suffer from chronic illnesses that increase their vulnerability.


Schools: Public schools present a particular challenge when it comes to cleaning and the overall managing of the environment. This results from budget constraints, limited maintenance and janitorial staff, outdated and malfunctioning cleaning equipment and inadequate cleaning products and staff training. Poorly designed and constructed schools also make adequate inspection and subsequent cleaning difficult.


Not surprisingly, poor indoor environmental quality (IEQ) in schools is common. Student performance and attendance is adversely influenced by contamination and pollutant exposure. Improper cleaning turns dust collecting reservoirs into sources of insect, animal and microbial antigens that can trigger asthma and respiratory illnesses especially during cold and flu season.


Major dust reservoirs/sources in schools typically lacking effective cleaning are carpet, animal cages and HVAC systems. Inattention to moisture throughout a facility encourages microbial growth and amplification, which contributes to poor air quality and exposes students to respiratory health risks. On a positive note, an increased effort to improve floor and desk cleaning has reduced upper respiratory symptoms.


Classrooms, hallways and other ecosystem sub-compartments (e.g., kitchens, restrooms and locker rooms/gyms) also collect dust. Cleaning these areas reduces the potential for infectious disease. Clean and sanitized school kitchens and related areas prevent the environment from being contaminated and bacterial pathogens, such as E. coli, Listeria and Salmonella, from being transmitted.


Similarly, cleaning and monitoring restrooms prevents student exposure and illness from enteric (noroviruses, E. coli) and respiratory (cold, flu viruses) pathogens. A study of two daycare centers found that 19 percent of the surfaces tested positive for rotavirus, notably drinking fountains, toilet handles and telephone receivers. Students describe these facilities as “unpleasant, dirty, smelly and frightening” and refuse to use them. Consequently, they may suffer from constipation, urinary tract infections and incontinence.


Likewise surfaces and materials in school locker rooms and gymnasium, if improperly cleaned and sanitized, increase the transmission of infectious agents, such as Athlete’s foot fungi (Staphylococcus aureus) and Herpes viruses. This creates the potential for widespread outbreak among students.


A recent review of the significance of fomites (inanimate surfaces) in spreading respiratory and enteric viral disease claimed that “the rapid spread of viral disease in crowded indoor establishments, including schools, daycare facilities, nursing homes, business offices and hospitals, consistently facilitates disease morbidity and mortality” and that the “level of cleanliness” is a contributing factor.


Carpet: Although school carpets usually are cleaned by an annual extraction process, ineffective maintenance and inefficient vacuuming during the year causes the carpet dust reservoir or “sink” to fill and become a pollutant source. Typically, carpeted classrooms are crowded with desks and other furniture. Manpower to rearrange it to effectively vacuum even weekly usually is lacking. Additionally, vacuum cleaners often capture dust inefficiently and may serve as aerosol generators, collecting dust and its pollutants and returning them to the environment.


As carpet becomes a pollutant source children are at risk of exposure to very fine or respirable particles (<5.0 µm) containing allergens from dust mites, cockroaches and cats (antigens are brought to school on clothing and shoes) and spores from allergenic molds, such as Cladosporium, Penicillium and Aspergillus. Research indicates dust from well maintained carpet can harbor over 1.5 x 105 mold spores and 1.0 x 107 bacteria per gram of carpet dust. If carpet is damaged by moisture or damp from inefficient cleaning for over 24 hours the fungi and bacteria grow and amplify rapidly.


In this situation the carpet’s fungal contamination, primarily as mold allergens and potential toxic metabolites (mycotoxins), increases significantly. The bacterial burden and its endotoxin source (bacterial cell wall components that react with lung tissue and are associated with respiratory illness) do too. The latter can induce fever, bronchoconstriction and chest tightness and increase airway reactivity. Endotoxins also boost inhaled antigen response.


Exposure to chemical pollutants may occur when children are subjected to respirable carpet dusts containing pollutant residues, including pesticides, cleaning products, lead and volatile organic compounds produced by microbial contamination. “Musty,” “moldy” or “mildew” odors signal carpet contamination. Carpet also may serve as a fomite or mechanical means of transmitting agents, such as head lice or fungi that cause skin infections, like ringworm. These are significant risks for children in lower grades who might spend time on carpet for most of the school day.


A U.S. Environmental Protection Agency (EPA)-sponsored study monitoring indoor air quality for biological pollutants was conducted before and during professional carpet cleaning in 16 commercial, public and residential environments. The sites included six clerical offices in high-rise buildings; four service-based business offices at ground level; five single-family homes; and one elementary school classroom. Data showed a strong relationship between routine carpet cleaning and maintenance and low levels of airborne fungi. Clerical offices had the lowest fungi levels while homes and schools had the highest. The clerical offices were rigorously maintained by daily vacuuming, monthly shampooing or bonnet cleaning and annual hot water extracting. The offices also had reduced track-in contamination by being above ground level and without animals or children. Conversely, the ground level homes and classroom had multiple pollutant sources and were cleaned and vacuumed infrequently.


Those results dramatically demonstrated the effort required to maintain a healthy carpet and prevent it from becoming a pollutant source. The Institute of Inspection, Cleaning and Restoration Certification’s (IICRC) Industry Carpet Cleaning Standard claimed that periodic extraction cleaning is necessary. This standard requires that carpet be dried quickly (<12 hrs.) to prevent microbial amplification. After cleaning it must be vacuumed frequently with high efficiency machines that provide maximum dust extraction and minimum dust resuspension to the air.


Careful attention to carpet cleaning, maintenance and moisture control prevents the carpet sink from becoming a pollutant source. Unfortunately, there usually are insufficient financial and personnel resources to implement such a program in schools. Consequently, serious consideration must be given to whether carpet should be installed. While hard surface flooring still requires routine cleaning and maintenance at comparable costs, it eliminates a possible pollutant source in classrooms.


Heating, ventilating and air conditioning system (HVAC): In a 15-year-old school building one-half of the occupants complained of a building-associated illness characterized by eye, nose and throat irritation, skin rash, headache and fatigue. Complaints also included a musty odor during the air conditioner season. Air handling unit plenums and major air supply ducts were lined with a porous insulation that gradually was permeated by organic dusts as a result of air filtration deficiencies.


Insulation below the cooling coils became amplification sites for fungi, such as Penicillium, and bacteria, such as thermophilic actinomycetes. Both produce spores that can be deposited in the upper and lower airways and result in respiratory illnesses. Airborne concentrations of these microorganisms in classrooms and offices were 100 times greater than in outdoor air. The acoustical insulation within air handling units and supply ducts became amplification sites for microorganisms.


Preventing air duct-related pollution in schools requires combining proper design and dedicated inspection, cleaning and maintenance. Internal porous insulation should be avoided in ductwork. Even if sealer liner is used internally, it still can entrap dust and debris and complicate the commercial dust cleaning process. Ducts can be insulated externally with fiberglass wrap. Any internal porous insulation that is a source of microbial contamination should be removed or the ductwork replaced. This should be done instead of using antimicrobials, biocides, sealants or encapsulants.


All HVAC system components must be designed and constructed to easily inspect cleaning and maintain all components, including filters, cooling coils and ductwork. Access doors should be large and easy to open to facilitate thorough and regular maintenance. Hinged access doors are preferable to bolted panels. Condensate drain pans must completely drain, thereby ensuring a large enough water reservoir to produce a microbial soup whose contaminants can be entrained into the building airflow. Many pans still are manufactured with the drain hole above the pan bottom.


Research remains incomplete regarding the effectiveness of various commercial duct cleaning practices for mitigating duct-related problems. Ensure a healthy school building by focusing on preventing pollutant problems through design and routine inspection, cleaning and maintenance.


Animals in school environments: Small animals in schools are valuable to a child’s education. They contribute to learning about biology, ecology, environmental science, behavior, geography and mathematics. They also are sources of environmental pollution. Children observe, feed, weigh, pet, handle and care for these animals. Teachers are responsible for providing an optimum environment for the animals and prevent their mistreatment. They also must be aware of the potential for adverse health effects to children in terms of allergic and infectious diseases.


The most insidious exposure affecting children in classrooms harboring animals, especially mammals, comes from airborne allergens. Animal dander and fungal and bacterial spores and toxins from fecal and bedding materials may induce or exacerbate allergic sensitivities. Asthma is the leading cause of elementary school absences and a major public health concern. Upper airway inflammation and irritation from allergen exposure increases susceptibility to colds, influenza, other viruses and bacterial infections, such as streptococcal sore throat. Animals also can transmit infectious agents through direct contact, like those causing salmonellosis and fungal skin infections. Children should only be exposed to the animals during class.


Dedicating one room to animals will minimize day-long exposures to allergic and infectious agents. Doing so also will remove active pollutant sources and facilitate the cleaning process. The room should have adequate cage racks and mechanisms for feeding, watering and cleaning. A dedicated exhaust ventilation system also is needed to carry dusts, dander, allergens and building odors. Rather than retrofitting an area, the concept should be addressed in the design or renovation phases or when determining heating, cooling, ventilating and maintenance requirements.


Healthy school building design: The design phase should address how to include floor coverings, animals and HVAC system access in cleaning school buildings. Design intervention helps to control indoor pollution when a built environment must match the indoor activities and when designing new buildings or remodeling older ones. Buildings and their furnishing design must facilitate cleaning that maximizes pollutant removal and minimizes chemical, biological, particle and moisture residues.


Hospitals: Preventing the transmission of infectious disease agents resulting in healthcare-acquired (nosocomial) infections is challenging for hospitals. It requires human and environmental source control, activity management, design and dilution intervention and cleaning.


Infection sources can be managed through removal, such as with mold-contaminated buildings, or modification. This includes purging hot water systems to eliminate Legionella species. Tuberculosis patients can be housed in negative-pressure rooms, required to wear respiratory protection or be placed in laminar-flow beds until they are no longer infectious. Environmental sources can be managed through building maintenance that ensures appropriate and routine inspection of potential sources, such as HVAC air intakes and filter banks, air ducts, cooling towers and hot water systems. Managing sources through efficient and routine cleaning and disinfecting deactivates and removes potentially infectious particles. It also reduces reservoirs, like carpet and dust-contaminated surfaces.


Managing activity guarantees the building is used for its original intent. Indoor pollutants may be encountered if the building or its parts are used for other purposes. Examples include laboratories located in offices or living quarters or offices located in former laboratories. Using a building for its original intent facilitates and promotes routine inspection, maintenance and cleaning programs. These programs may become an afterthought when a hospital is continually renovating the existing structure, constructing additions or modifying the built environment.


Design intervention also is crucial to healthcare facilities. This may include special exhaust ventilation, airflow requirements or removing and excluding certain building or furnishing materials susceptible to microbial contamination, like ceiling tile and carpet. The dilution process may lower airborne concentrations of pollutants through cleaner air.


Small infectious particles, or droplet nuclei, can be moved by air and captured by air filters. One study investigated the effectiveness of in-room air filtration with dilution ventilation to control TB infection. Results showed that ventilation and recirculating air filtration can reduce droplet nuclei concentrations with 30 to 90 percent effectiveness. Combined with source management approaches, such as treatment booths and respirators, transmission potential in high-risk settings could be lowered significantly. Similarly, in controlling nosocomial aspergillosis, high air exchange rates are the most effective, particularly when combined with point-of-use filtration.


Cleaning is the final defense in managing indoor environmental contamination. Even if source and activity management, design intervention and dilution ventilation are used to control infectious aerosols, cleaning still is necessary.


The importance of cleaning was demonstrated in a year-long study of cleaning effectiveness in a non-compliant, multi-use building. The building housed laboratories, offices, medical examination rooms and a daycare unit with 62 children. Routinely using high-efficiency vacuum cleaners, damp dusting and less polluting cleaning products on hard surfaces decreased particulate and microbial contamination on surfaces and in air. It also reduced volatile organic compounds (VOCs). This was particularly true in high traffic areas and when entryway mats were installed for reducing track-in and rapid attention to events, such as leaks and spills. After seven months of improved cleaning practices and environmental monitoring, data showed meaningful decreases in airborne dust mass (50 percent), fungi (61 percent) and bacteria (40 percent); carpet dust fungi (40 percent) and bacteria (84 percent); and endotoxin (72 percent) over the previous 5 months.


Data also revealed intricate information about the indoor ecosystems and how source management and cleaning stabilizes microenvironments and prevents pollutant buildups that compromise health and valuable materials. For example, quantitatively measuring airborne and carpet dust mass showed an inverse relationship. When carpet dust is disturbed and re-suspended its levels decrease while airborne dust levels increase. Conversely, as airborne dust settles on carpet total airborne dust mass decreases and carpet dust mass increases. Airborne biopollutant monitoring also showed occasional spikes of Penicillium, Aspergillus and gram-negative and actinomycete bacteria. This demonstrated that the indoor environment is indeed an ecosystem with normal fluctuations that are controllable through routine cleaning and immediate attention to unexpected occurrences.


Daycare, nursing home and home healthcare environments: These environments present significant infectious, allergic and toxic exposure risks to susceptible occupants and require effective cleaning practices. Unlike adults, pre-school children have higher respiratory and heart rates, different oral behaviors and immature liver, kidney and immune functions. The elderly, especially nursing home residents, suffer from a naturally waning immune function and that which is treatment-induced, often in conjunction with chronic diseases.


Individuals convalescing at home from chemotherapy, organ transplants, AIDS or other medical conditions also are vulnerable to infectious and toxic effects from indoor pollutants. To decrease exposures in these environments, indoor environmental reservoirs must be cleaned routinely. Soil and associated pollutants should be removed by using detergent products on hard surfaces. This cleaning approach significantly decreases pollutants and minimizes germicides that may leave biological and chemical residuals as contaminants. A recent study confirmed the effectiveness of vacuuming and wet washing to remove lead-contaminated house dust. Another study showed the effectiveness of combining moisture control, cleaning and targeting disinfectant use to reducing potentially allergenic and opportunistic molds. These studies emphasize the possibility of instituting non-polluting indoor cleaning practices.


Public transport environments: Threats of pandemic respiratory disease and bioterror incidents focus on effective cleaning and decontamination procedures for public transportation. In these situations, the pollutants must be physically removed. This sanitization can combine HEPA vacuuming with a practical wet cleaning/sanitizing method that effectively reduces pathogens to below an efficient threshold and minimizes the chemical pollutants introduced into an environment. This approach presents a practical and feasible alternative to the extensive use of chemical germicide sprays and gases.


Conclusion and recommendation: The indoor environment is a delicate, complex ecosystem where contaminant reservoirs easily become pollutant sources through an ineffective and infrequent reduction and removal process called cleaning. To maintain an ecological balance and promote a healthy indoor environment, effective cleaning practices for preventing and remediating biological, chemical and particulate pollution in special indoor environments must be routinely identified, evaluated and implemented. This can only be done through a dedicated and sustainable cooperative industry effort regarding cleaning science research.

Eugene Cole, Ph.D., of Brigham Young University’s Dept. of Health Science is a respected microbiologist, public health teacher and research specialist on cleaning and health. He also is a member of CIRI’s Science Advisory Council.

Published with permission by the Cleaning Industry Research Institute © 2011.


Cleaning and Special Environments:  Created on April 1st, 2011.  Last Modified on April 1st, 2011


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Other Articles by Dr. Eugene Cole

About Dr. Eugene Cole

Eugene Cole, Ph.D., of Brigham Young University’s Dept. of Health Science is a respected microbiologist, public health teacher and research specialist on cleaning and health. He also is a member of CIRI’s Science Advisory Council.

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