Guideline 18.1

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Guideline 18.1: Hardware and controls that reduce particulates and chemical pollutants are utilized

How can the air handling system be used to reduce particulates and chemical pollutants?

The following strategies work most effectively if the exhibit space is properly sealed:

• Filter the air. Air filtration can provide protection from particulates at a variety of levels, depending on the severity of the pollution problem and the sensitivity of the collections. At a minimum, the air entering the museum’s heating and cooling systems should be filtered to remove particulate matter larger than 1 micron. Recirculated air should also be filtered.
• Upgrade the HVAC System. Dust attracts and holds pollutants. Therefore, particulate filtration will also capture a certain amount of chemical pollution.
• Incorporate activated carbon or potassium permanganate filters into the system in areas that are highly polluted or to protect sensitive collections. Such filters should reduce sulfur and nitrogen dioxides to a level below 10 micrograms per cubic meter of air.
• Prefilter or exhaust polluted air directly from the building. Air from areas within the museum known to generate pollutants—including exhibition preparation areas such as spray booths and printing facilities—should be prefiltered or exhausted directly out of the building.
• Provide good air circulation. [How is good air circulation provided?] This helps prevent the concentration of pollutants. However, avoid a high rate of unfiltered airflow across the surface of an object because it increases the total exposure to potential pollutants.
• Adjust the air handling system to create a positive room pressure to further limit the influx of potentially polluted external air.
• Reduce the amount of air taken in from outdoors to improve the efficiency of the filtration. The system must be operated within the minimum requirements set by the American Society of heating, refrigeration, and Air-conditioning Engineers (ASHRAE).
• Maintain a moderate climate. Elevated temperature and relative humidity accelerate the evolution of chemical pollutants; therefore maintaining a moderate climate helps with pollutants control. Additionally, wide fluctuations in temperature and RH can cause localized condensation that results in elevated pollution levels and reaction with object surfaces. (See Standard 19 for regulating temperature and RH).
• Use localized filtration equipment as needed. If improving filtration throughout the museum is not feasible, consider using room-sized units in a confined space such as an exhibit preparation area, an exhibit space during construction, or a finished exhibit. Some commercial units remove more than 99% of particulates down to a size of 0.3 microns; many also incorporate an activated carbon prefilter that removes chemical pollutants.

What air filters are appropriate for use in exhibits?

• The most effective High-Efficiency Particulate-Arresting (HEPA) filters provide more that 99% efficiency for particulate matter as small as 0.01 microns. Providing that the equipment can operate under lower air pressures, replacing panel filters with media or HEPA filters provides a dramatic improvement in air quality.
• Media air filters, which are often pleated to increase surface area and to help limit the subsequent drop in air pressure, are more efficient than residential-use filters and can remove up to 35% of particles larger than 0.5 microns.
• Dust and lint filters used in residential systems, also called panel filters, are generally not effective enough for museum applications because, at best, they only remove particulate matter larger than about 10 microns.

Pollutant	Particle size (in microns)	Filter Efficiency
Soil dust	100 - 1	N/A
Coal dust	100 - 1	N/A
Household dust	5 - 0.01	Panel filters (10)
Insecticide dust	9 - 1	N/A
Tobacco smoke	5 - 0.01	Media filters (0.5)
Carbon particulate	1 - 0.001	HEPA filters (0.01)