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Portable Classrooms

Indoor Air Quality Design Tools for Schools

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Portable, or "relocatable", classrooms have been a feature of many school districts for years. From a district's perspective, the two advantages of portable classrooms are low initial cost and short time between specification and occupancy. They are intended to provide flexibility to school districts, enabling quick response to demographic changes and providing the ability to be moved from one school to another as demographics change. In reality, portable classrooms are seldom moved and become permanent fixtures of the school.

Recent surges in student population fueled an explosion in the use of portable classrooms in many parts of the country, raising concerns about the healthfulness of portable classrooms.

The most common problems with portable classrooms include:

The effects of poor indoor air quality in portable classrooms are no different than those in permanent classrooms. All school buildings use similar construction and furnishing materials, so the types of chemicals present in indoor air are not likely to be different for portable versus permanent classrooms. However, pressed-wood products which may contain higher concentrations of formaldehyde are used more in the factory-built portable units than in buildings constructed on-site. As result, levels of airborne chemicals may be higher in new portable classrooms, especially if ventilation is reduced.

Although portables are often the lowest cost option for housing students, they range in quality. Care should be taken during specification and selection to ensure that the students' health is not compromised for inexpensive, low quality designs. When districts specify a portable design, they typically create a term contract that other districts can use to purchase the same (or slightly different) design. This practice (often called "piggy-backing") can save a district valuable time and money on specifications and approvals, but it can also compound poor decisions made in the original procurement.

Like all school facilities, portable classrooms should contain appropriate building and indoor surface materials and properly designed ventilation systems to minimize the presence of indoor pollutants. Commissioning and regular maintenance are also important to maintain the quality of the indoor environment.  The recommendations applicable to school facilities also apply to portable classrooms.  Following are some of the most important considerations of specific relevance to portable classroom design, commissioning, and maintenance.

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Specifying New Portable Classrooms

  Specify the appropriate vapor barrier location for exterior wall construction, consistent with the climate where the classroom will be used.
  When specifying a new portable classroom, ensure that the HVAC system can: (a) provide a minimum of 450 cfm (based on 30 occupants at 15 cfm/occupant) of outside air; and (b) heat and cool this volume of outdoor air at design outdoor temperatures for the specific geographic location where each classroom is installed.
  Some manufacturers of portable units do not include outdoor air intakes in their standard classroom models. It is important that an additional "outdoor air kit" be ordered for this purpose. Further, installation of an outdoor air intake must be specified as part of the exhaust system.  Outdoor air intakes should not be located under portable units; these areas are typically not well ventilated and are prone to moisture, biological contaminants and other pollutants. Lack of an exhaust in the HVAC system with an outdoor air intake will result in inadequate removal of pollutants from the room.
  Outdoor air should be supplied continuously when a classroom is occupied. Demand-controlled HVAC package systems often used in portable classrooms typically operate only when the temperature of a space is different from the thermostat’s set point. In order to provide a continuous outdoor air supply, it is important to ensure that the HVAC thermostat fan switch is set in the "on" or continuous mode when occupied.
  Air filters are needed for protection of HVAC components and reduction of airborne dust, pollens and microorganism from re-circulated and outdoor air streams. Air filters should have a dust-spot rating between 35% and 80% or a Minimum Efficiency Rating Value (MERV) of between 8 and 13.
  If carpet is specified, use carpet that has been tested under the Carpet and Rug Institute’s Indoor Air Quality Carpet Testing Program.
  Do not use carpet in entryways to classrooms with direct outdoor access. Supply waterproof mats over carpeted entryways and other areas used for drying clothing and umbrellas.
  Locate classroom away from locations where: (a) vehicles idle, (b) water accumulates after rains, or (c) there are other major sources of air pollution.
  Ensure that at least one supply air outlet and return air inlet are located in each enclosed area.
  Ensure that building air intakes are located away from any exhaust outlet(s) or other contaminant sources.
  Specify operable windows to provide user-controlled ventilation when needed.
  Consider covered entries with an exterior entry mat.
  Check that special-use classrooms (e.g., for chemistry, biology, fine arts, etc.) have local exhaust ventilation (e.g., hoods or window fans) and appropriate ventilation rates.
  Locate HVAC and air handler units as far away as possible from teaching areas to reduce noise.
  If specifying duct board or internal duct lining for thermal and/or acoustical control, be sure to consider the potential for uncontrolled moisture to enter the duct over the life of the system.
  Ensure that HVAC ducts and plenums have easy access for inspection and cleaning.
  Specify that low VOC emitting building materials be used in construction.
  Specify complete documentation of operation and maintenance requirements.

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Commissioning

See also www.epa.gov/iaq/schooldesign/commissioning.html

  Prior to use of any new portable units by staff or students, operate HVAC systems at their maximum outdoor air intake rate continuously for several days. Start the "flush out" as soon as the HVAC system is operational, and continue after furniture installation.  During this period, do not re-circulate return air.  Outdoor air should be thermally conditioned (i.e., heated or cooled), as needed, to typical indoor temperatures.
  Measure the amount of outdoor air entering the outdoor air intake of the HVAC unit to ensure it meets or exceeds the amount specified or 15 cfm per person, whichever is greater.
  Do not "bake-out" the unit. "Bake-out" is defined as increasing temperatures up to 100F in order to "artificially age" building materials. It's effectiveness has not been proven and it may in fact damage parts of the HVAC system or building components.
  Continue "flush-out" ventilation during periods of first use. Efforts to minimize exposures of school children and staff to building material emissions should continue in the weeks following construction. Emissions of VOCs are highest during this period. Flush-out periods of 1-2 weeks are recommended, although longer periods may be required. For the first days to weeks of occupant use, continue to operate HVAC systems at the maximum outdoor air setting. Finally, monitor occupants’ comfort, and follow-up complaints to identify problems early.
  Establish and implement an Integrated Pest Management plan.

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Operations and Maintenance

  Provide training on operation and maintenance of new HVAC equipment to appropriate staff. Be certain that operation and maintenance documentation is kept readily accessible to staff servicing the system.
  Allocate sufficient staff time and funds for maintenance.
  Instruct teachers and staff on proper use and settings of thermostat and ventilation controls – provide each classroom with hardcopy (plastic-covered) instruction sheets.
  Establish a regular and timely plan for testing, inspecting, and performing specific maintenance tasks. Inspect roofs, ceilings, walls, floor, and carpet for evidence of water leakage or stains, and for mold growth or odor. Replace water damaged materials promptly and fix leaks as soon as possible.

  • Inspect air supply outlets and return air inlets, to ensure that they are open, operable and unobstructed.
  • Check airflow rates at the outlets and inlets periodically.
  • Inspect air plenums for mold growth, excess dirt, or obstructions.
  • Establish a periodic air filter replacement schedule.
  • Clean condensate pans (monthly) and do not allow free standing water to accumulate.
  • When carpets are cleaned, ensure that proper procedures are followed for moisture extraction and provide adequate ventilation for them to dry within 24 hours.
  • Provide for the proper storage of cleaning/janitorial supplies (preferably in a separate building or separately exhausted closet).
  • Maintain documentation of completed tasks.

References and Resources

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