IAQ in Schools
This section provides an overview of indoor air quality (IAQ) in schools and its influence on the health, performance, and absence of occupants of schools. The review is based on papers published in peer reviewed journals. Most of the research has been performed in public schools, particularly elementary and secondary schools. The review focuses on allergens, volatile organic compounds (VOCs), particles, dampness and mold, and ventilation with outdoor air in schools. Topics not covered in this review include temperature and humidity, lighting, acoustics, and special IAQ issues related to construction and renovation.
The main findings of related scientific research are as follows:
Concentrations of allergens in floor dust are commonly considered a proxy for allergen concentrations in air and are used to indicate the potential for allergen-related health effects. Concentrations of pet allergens in dust from classrooms are often higher than concentrations in dust from homes without pets. Concentrations of allergens from pets, cockroach, and mice in the dust of classrooms often exceed the levels associated with development of allergic sensitization in homes. Available data suggest an association of adverse allergy and asthma outcomes with increased cat allergen in schools. Pet allergen is transported into classrooms on the clothes of children with pets at home. Other than prohibiting pets at school, there may be no viable options for school personnel to reduce the sources of these allergens in schools. Improved space cleaning will likely help reduce concentrations of these allergens in classrooms, but the effectiveness of cleaning has been inadequately studied. Measures likely to reduce cockroach and mouse allergens in schools include better housekeeping and building maintenance and integrated pest management practices.
Volatile organic compounds (VOCs) in indoor air come from a large number of sources including building materials, furnishings, consumer products, tobacco smoking, cooking, people and their activities, indoor chemical reactions, and outdoor air. VOCs may be odorous and some VOCs are known or suspected to cause a variety of adverse health effects. Concentrations of VOCs in the air of schools are typically moderate and less than VOC concentrations in homes. Among VOCs in schools, formaldehyde and terpene concentrations are often highest. Building materials and furnishings are usually a key source of formaldehyde. Cleaning products, new wood products, and outdoor air are sources of terpenes. The available data suggest a possible association of increased respiratory health effects with increased formaldehyde concentrations; however, the data are insufficient for firm conclusions. The estimated cancer risks of VOC exposures in classrooms are on the order of 10 per million, but can be higher in specific classrooms. Reducing indoor sources and ventilation with outdoor air are the primary options for controlling VOC levels in classrooms.
Many studies have found that higher concentrations of particles in outdoor air are associated with increased respiratory health effects and premature death. Particles in the air within schools are partly from outdoor air and partly from indoor sources. Concentrations of particles in the air within schools are often well above health-based guidelines for particle concentrations in outdoor air. The frequently high indoor particle concentrations in schools relative to guidelines suggest a high potential for adverse health effects. Several studies have also found statistically significant increases in respiratory health effects among staff or students in classrooms with higher particle concentrations. Together, these findings indicate that increased attention should be placed on reducing particle concentrations in schools. Increases in outdoor air ventilation rates can help reduce particle concentrations in many schools because indoor particle concentrations usually exceed outdoor air concentrations; however, increased ventilation is a poor solution where the outdoor air is highly polluted. Improvements in particle filtration systems, or addition of filtration systems when they are absent, can be practical options.
The relatively consistent findings of a substantial number of quality studies, and the results of a meta-analysis, indicate that there is an association of dampness and mold in schools with increased respiratory health symptoms, particularly with cough or wheeze, among occupants of the schools. Visible dampness and mold or mold odor are more clearly associated with increased health symptoms than are higher levels of mold in air or dust. Objective (measured) health measures such as lung function or markers of allergic or inflammatory responses are less consistently associated with dampness and mold in schools. Overall, these findings from studies in schools mirror those available from a larger body of research on dampness and mold in homes. Improvements in building design, construction, operation, and maintenance practices are the key to prevention of dampness and mold in schools. When problems occur, the sources of moisture should be promptly addressed and contaminated materials cleaned or replaced.
Rates of ventilation of schools with outdoor air influence indoor air pollutant concentrations and building energy consumption. Indoor concentrations of carbon dioxide serve as an easily measured proxy for ventilation rates in schools, with higher carbon dioxide concentrations indicating lower ventilation rates. Carbon dioxide data from surveys in schools indicate a widespread failure to provide the minimum amount of ventilation specified in standards for classrooms. Often, ventilation rates fall far short of the recommended minimum ventilation rates. A substantial body of research provides compelling evidence of an association of improved student performance with increased classroom ventilation rate. Other research suggests improvements in measures of respiratory health with increased ventilation rates, but the evidence of improvement in health is not as compelling as the evidence of improvements in student performance. The available research indicates that increased ventilation rates in classrooms are associated with reduced student absence. There are very few published studies of methods to prevent and remediate the widespread problem of low ventilation rates in schools; thus, the following comments rely substantially on judgment. It is clear from the carbon dioxide data in naturally ventilated schools that schools cannot consistently rely on occupants to open windows sufficiently to provide the recommended minimum ventilation rates. Carbon dioxide sensors that provide a visual warning signal when carbon dioxide concentrations are elevated may help to prompt windows use. Mechanical ventilation with outside air is recommended and the ventilation control systems need to assure that sufficient ventilation is provided even when the need for heating and cooling is minimal. Mechanical ventilation systems should not be noisy because noisy systems are often turned off.