Consensus Best Practice Principles to Achieve and Maintain Healthy Indoor Air

Adopted by the Board of Directors of the

Maine Indoor Air Quality Council

January 17, 2001


The quality of the school indoor environment can have significant impact on health and well being. Many indoor air quality problems are associated with general symptoms of malaise (headaches, fatigue, irritability, nausea, dizziness, diminished ability to concentrate). Also, increased levels of irritants and allergens in the indoor air can contribute to specific problems related to asthma, sinusitis, and other respiratory diseases. Finally, exposure to toxic substances (such as carbon monoxide, asbestos, radon, lead, and mercury) may produce serious health effects if exposures are not controlled adequately.

The purpose of this document is to outline guidance regarding the best practice principles for achieving and maintaining healthy indoor air quality in Maine’s schools. These recommendations are based on the public health principle that prevention of indoor air quality problems is of prime importance to overall lung health.

In reviewing this document, it is important to consider a couple of general matters related to the context. First, perception of air quality may be influenced by other factors within the indoor environment, such as lighting, odor, and temperature. While beyond the scope of this document, they are important factors to incorporate within a more comprehensive approach to managing indoor environments.

Second, the recommendations presented in this document are intended to be helpful for all school environments. They are not limited solely to those facilities within the purview of the Maine Department of Education or the Maine Bureau of General Services (e.g., vocational and technical centers, colleges, and universities). The Task Force on School Air Quality recognizes that there will be different implementation considerations depending on the type of school involved.


School air quality problems often originate and worsen through lack of attention to commonly recognized principles of building maintenance and operations. These principles fall into three general categories: ventilation, moisture control, and pollutant control.

The process of achieving and maintaining healthy indoor air quality in schools is a collective responsibility. The best means for meeting this objective is through proper building commissioning and the establishment of cross-disciplinary teams with a designated indoor air quality manager. At a minimum, these teams should consist of a school administrator, school nurse, facilities manager, and teacher. The EPA Tools for Schools Action Kit provides guidance for the functioning of these teams.

There is insufficient evidence to support the establishment of new environmental standards for schools at the present time. Efforts should be focused on following best practice protocols for building maintenance and operations, on ensuring conformity with the minimum requirements already in statute, and on further clarifying the health significance resulting from exposure to toxic substances present in the school environment. Guidance regarding the best practice protocols is outlined in the recommendations. Existing statutory requirements include:

  • ASHRAE Minimum Ventilation Standard (Title 5 MRSA, Chapter 153, Section 1742, No. 24)
  • School Building Ventilation requirements (Title 20-A MRSA, Chapter 223, Section 6302)
  • Maintenance and Capital Improvement Program (Title 20-A MRSA, Section 4001)

Each school administration should possess adequate knowledge of how the building is designed to operate, and provide assurance that the building is in fact operating within the design parameters.

Application of sound building maintenance and operation principles warrants adequate education and training of school personnel.

The Bureau of Health and the Board of Pesticides Control should be consulted on the need for specific health guidance regarding exposure to toxic substances such as carbon monoxide, asbestos, radon, lead, mercury, and pesticides.


There is currently no set of air standards that can be used as a comprehensive measure of indoor air quality. Rather, the healthfulness of the indoor air depends on the effective coordination of three major pollutant prevention and control strategies:

(1) Sufficient ventilation;

(2) Moisture control; and

(3) Control of dust and chemical pollutant sources.

These strategies can be achieved through proper building commissioning and preventive maintenance.


A. General Ventilation

1. All school ventilation systems should strive to achieve the ASHRAE outdoor air ventilation standard for the design population, as specified in the state building standards code (Title 5 MRSA, Chapter 153, Section 1742, No. 24,, currently a minimum of 15 cubic feet per minute per person (cfm/person), introduced to allow maximum circulation in the occupied space during school activity hours.

2. All school ventilation systems should be maintained and operated to provide at least the quantity of outdoor air required in effect at the time of installation, and operated continuously during school activity hours.

3. While having operable windows is desirable, natural ventilation cannot ensure that the ASHRAE standard will be met. Therefore, natural ventilation should not be considered a substitute for a properly designed and operated mechanical ventilation system, and should be used primarily as supplemental ventilation to reduce overheating during intemperate weather.

4. A properly designed and operated ventilation system should control carbon dioxide levels to meet ASHRAE guidance, assuming no sources other than human activities are contributing to carbon dioxide levels.

5. If the building is found to have an environmental or health problem that is not related to specific sources that can be removed, and the ventilation system is not delivering 15 cfm/person, the system should be upgraded to deliver this amount of outdoor air.

6. Upgrades to the building envelope (e.g., windows, walls, roofs) may influence the ventilation characteristics of the building. Therefore, upgrades to the building envelope must in their planning and design specifically address the impact on indoor air quality. If warranted, ventilation system upgrades should be incorporated. These ventilation system upgrades may apply to minor as well as major renovations.

7. Ventilation system performance assumes that normal occupancy limits are not exceeded. Occupancy limits of classrooms should be kept on record at the school. Attention should be given to the criterion that class sizes not exceed these occupancy limits.

8. Carbon dioxide demand control strategies may be incorporated to minimize excessive energy while maintaining acceptable indoor air quality. Generally, ventilation systems operating on carbon dioxide sensors are not feasible on a school wide basis, although they can be very cost effective in certain areas (e.g., gyms, cafeterias). When carbon dioxide sensors are incorporated, the ventilation systems should deliver at least 0.05 cubic feet of outside air per square foot when the ventilation systems are on, and the area is not occupied.

B. Local exhaust ventilation

1. Separate Ventilation for Restrooms and Janitorial Cleaning Supply Rooms. Restrooms and janitorial cleaning supply rooms should be ventilated directly outside the building with no recirculation to the rest of the building. Per ASHRAE 62-1989, exhaust standards should be 50 cfm per water closet and per urinal. Exhaust may be through heat recovery equipment if it is part of a school-wide system and meets Maine codes.

2. Separate Ventilation for Office Equipment. Due to the considerable amount of pollutants associated with office equipment (e.g., toners from copiers and fax machines), areas containing this equipment should have ventilation designed to remove generated pollutants and should exhaust outside the building with no recirculation to the rest of the building.

3. Special Considerations for Science Labs, Kitchens, and Art Rooms. Because of the unique pollutants and contaminants associated with these areas, they should be constructed, operated, and maintained in accordance with applicable standards (e.g., OSHA).

4. Special Considerations for Technical Education Areas. Because of the high amount of pollutants generated in these areas, they should receive higher ventilation in accordance with ASHRAE standards, and with systems for positive engine exhaust withdrawal and local exhaust requirements for other activities (e.g., painting and welding) consistent with all Occupational Safety and Health Administration (OSHA), American Council of Governmental Industrial Hygienists (ACGIH), and EPA regulations and standards. Exhaust in such areas should be vented directly to the outside of the building.

5. Local exhaust ventilation systems should be properly designed so as to be compatible with general ventilation criteria, and be provided with designedmake up air. Exhaust shall be designed in accordance with ASHRAE fundamentals to minimize entrainment back into the facility.

C. Combustion Pollutants

1. All combustion pollutants should be properly vented to the outside. Re-entrainment of combustion gasses to the indoor spaces should be minimized through stack design consistent with Good Engineering Practice methods.

2. Carbon monoxide (CO) is a combustion byproduct with life threatening consequences. All schools should have a plan for identifying and responding to CO emergencies.

D. Air Handling Units

1. Ventilation systems should include filters within the design specifications of the manufacturer to protect the equipment, and to minimize the introduction of pollen and mold spores into the facility from the outdoors.

2. Final filter efficiency should be in the range of 45% to 85%, when tested in accordance with ASHRAE Standard 52.1, Atmospheric Dust Spot Method.

3. Drain pans should be sloped with drain outlet at the lowest point, and should drain completely under all operating conditions.

4. System components should be accessible for cleaning.

E. Temperature and Comfort

1. Room temperature should be kept within the comfort zone specified by ASHRAE during school activity hours.

2. High humidity can be directly controlled through the use of air conditioning and dehumidification systems. While this may be desirable, few school buildings currently have these systems in place.

3. Because of Maine’s cold climate, complaints related to low relative humidity may occur during the winter months. Humidification of the air is generally discouraged, due to its potential to create or aggravate microbial contamination inside of buildings. Measures to guard against over-ventilation of the indoor environment may help address problems associated with air that is perceived to be too dry.


A. Schools should be designed and maintained to prevent intrusion of water from outside the building. Water should be directed away from the building. Snow should be prevented from entering air intakes. Water vapor transmission through concrete should be prevented as much as possible.

B. Priority should be given to prevent growth of mold and other micro-organisms due to high relative humidity within the building.

1. The building should be sufficiently insulated to prevent contact of warm indoor air with cold surfaces (such as floors, walls, and pipes).

2. Internal moisture sources (e.g. showers, cooking) should be vented directly to the outside.

C. A plan should be in place to prevent microbiological contamination from water leaks. This plan should include:

1. Mechanisms to stop leaks or to direct water away from porous building materials;

2. A procedure to dry contaminated materials within 24 hours;

3. A procedure to remove and replace water damaged materials safely.

D. When water contamination does occur, priority should be given to identifying the contaminated areas, preventing further contamination, and removing the contaminated materials in accordance with acceptable industrial hygiene practices.

E. Testing for biological contaminants should not be conducted as a routine part of building assessment, as there are no standardized test methods and no standards to evaluate the test results.

F. Renovations involving the removal and replacement of water contaminated materials should be conducted in a manner that prevents worker exposure and recontamination of the surrounding areas.

G. Carpet cleaning should be conducted during dry weather and with appropriate ventilation to avoid humidity related problems.


A. Dust control

1. Floors need to be cleaned on a regular basis to prevent the build up of dust and other pollutants. Equipment and staffing should be adequate to meet this need.

2. Chalkboards, desks, and other classroom items should be cleaned on a regular basis. Equipment and staffing should be adequate to meet this need.

3. Dirt collection devices at the entranceways of schools are recommended as a source control measure for dust within the building.

B. Cleaning solvents

1. Cleaning solvents should be used in accordance with the manufacturer’s instructions.

2. Individuals using cleaning solvents should be properly trained on the appropriate hazard communication procedures.

C. Measures should be taken that protect the health of workers and the school population at large from the harmful effects of pollutants generated during renovations (VOCs, dust, mold, etc). Recommendations from accepted guidance documents (e.g., the Sheet Metal and Air Conditioning Contractors National Association’s (SMACCNA) IAQ Guidelines for Occupied Buildings Under Construction) should be followed.

D. Schools should follow integrated pest management procedures, as outlined by the Maine Department of Agriculture. The Board of Pesticides Control should be consulted regarding the use of pesticides in schools. Usage should be in accordance with state and federal laws.

E. The presence of furry or feathered animals in the school may present risks to individuals with asthma and related conditions. Policies should be established within the school or school district to ensure protection of these sensitive population subgroups.

F. Carbon monoxide and other specific substances potentially present in the school environment may present serious health risks if not properly controlled. These substances include asbestos, radon, lead, and mercury. The Bureau of Health should be consulted regarding exposures to toxic substances in schools.

G. Environmental tobacco smoke is a recognized human carcinogen and a trigger of asthma attacks. Exposure to ETS should be eliminated on school grounds wherever possible.


A. Every school building should be commissioned and maintained to ensure that fully functional systems are properly operated throughout the useful life of the building. All efforts related to commissioning should be specified in the contract documents.

B. The process of maintaining healthy indoor air quality in schools is a collective responsibility. The best means for meeting this objective is through the establishment of cross-disciplinary teams with a designated indoor air quality manager. At a minimum, these teams should consist of a school administrator, school nurse, facilities manager, and teacher. The EPA Tools for Schools Action Kit provides guidance for the functioning of these teams.

C. Ventilation Systems

1. Before a newly constructed building (or addition or significant renovation) is occupied by students and staff, the HVAC system must be tested and balanced. An air balance report should be completed by a certified technician and a licensed engineer should certify that the HVAC system performs in all modes consistent with all aspects of its design. It is recommended that the certifying engineer be present when the balancing test is performed. It is further recommended that an additional air balance test be performed after one year of operation. The purchasers of the system should seek a system with the longest warranty.

2. Schools should be inspected periodically to ensure that the ventilation equipment is functioning properly, including operation of controls and outside air introduction.

3. School buildings should be constructed with the understanding that ventilation systems are active components in the operation of the building. They should be accessible to maintenance staff without the use of temporary ladders or the need to move occupants.

4. The school should always have access to expertise knowledgeable of the ventilation system. There should be a basic level of knowledge within the school staff. The roles and responsibilities of outside assistance should be clearly defined.