Dust and Particulates in Exhibits
- Monitor pollutants and enclose sensitive objects. Incorporate air filters in ventilated case designs or seal exhibit enclosures sufficiently to prevent particulate entry. (see TechNotes Monitoring Pollutants Inside an Exhibit Case)
- Use high-efficiency filters. HVAC equipment should remove particles down to 1-0.3 microns (60-80%). Change filters regularly.
- Use localized filtration equipment as needed. If improving filtration throughout the museum is not feasible, consider using room-sized units in construction areas or within the exhibit space.
An accumulation of dust can obscure or stain an object's surface, reducing its visual impact or interpretive usefulness. Oily and sooty deposits, in particular, may be impossible to remove from porous or fragile surfaces. Particulate matter ranges in size from visible to microscopic.
Particulate pollution is drawn into a building through natural ventilation and the environmental control systems, and can result from lack of appropriate dust control during renovation and exhibit construction projects, visitor traffic, and lack of appropriate filters in the building management equipment. Particulate matter (dust in the air around us) is a complex mixture of airborne soil, carbon soot, textile fibers, microorganisms, and protein materials. This combination can be abrasive, attract moisture, and encourage insects, fungi, and mold.
The ambient air quality will depend on local pollution sources and wind direction. Data about the amounts of particulate matter in the ambient air of many cities can be obtained from the U.S. Environmental Protection Agency and regional weather and air quality control stations. In addition, dust generated in the museum will add to the ambient particulate matter.
Various methods of reducing particulate pollution in exhibits are available:
- Limit the infiltration of unfiltered air through cracks and gaps in the building by caulking or gasketing doors and windows.
- Keep windows closed.
- Incorporate a vestibule at the exhibit entrance to control airflow.
- Use grates to capture dirt from visitors' shoes.
- Creating a positive room pressure through adjustments of the air handling system will further limit the influx of potentially polluted external air.
- Use appropriately rated filters in HVAC system(s)
Control particulate matter through a combination of macro and micro solutions, including enclosing sensitive objects and providing adequate filtration.
No matter what the ambient level of particulate pollution, any museum collection should be protected from gross amounts of dust. Protection can be provided at a variety of levels, depending on the severity of the pollution problem and the sensitivity of the collections. At a minimum, filter the air entering the museum's heating and cooling systems to remove particulate matter larger than 1 micron; use appropriately rated filters on HVAC system(s).
|Particulate Matter||Particle Size (in microns)||Filter Efficiency|
|Soil dust||100 - 1|
|Coal dust||100 - 1|
|Household dust||5 - .01||Panel filters (10)|
|Insecticide dust||9 - 1|
|Tobacco smoke||5 - .01||Media filters (.5)|
|Carbon particulate||1 - .001||HEPA filters (.01)|
Particulate Pollutants and Filtration
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. Media air filters, which are often pleated to increase surface area and to help limit the subsequent drop in air pressure, are more efficient and can remove up to 35% of particles larger than .5 microns. The most effective HEPA (high-efficiency particulate-arresting) filters provide more than 99% efficiency for particulate matter as small as .01 microns. As long as the equipment can operate under lower air pressures, replacing panel filters with media or HEPA filters provides a dramatic improvement in air quality.
Keep HVAC systems well-maintained, and clean humidifiers, cooling coils, and drains regularly. To prevent salt and mineral deposits from hard water (also called white dust accretions) from settling on museum collections, supply ultrasonic humidifiers with distilled water.
Reducing the amount of air taken in from outdoors can improve the efficiency of the filtration, although the system must be operated within the minimum requirements set by the American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE). Visitor traffic and necessary staff functions, including exhibit construction, create particulate matter; recirculated air must also be filtered.
If cost or practicality prohibit filtration of the entire museum building, room-sized air cleaners are very effective when used 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 particulate down to a size of 0.3 microns; many also incorporate an activated carbon prefilter that removes gaseous pollutants.
When objects on display are particularly susceptible to damage from dust buildup, the optimum level of protection is provided by enclosing them inside a case. A sealed exhibit case restricts airflow so that particulates are not drawn into the exhibit case. Air movement through a ventilated case must be filtered to remove particulate matter.
Guideline: Mitigating Pollutant Hazards
Appropriate measures [design, hardware and policies] must protect objects from exposure to pollutants
OR: The exhibit design must provide exhibit objects the required level of protection from exposure to pollutants
Pollutants come in the form of either particulates or chemical contaminants. These can corrode or abrade museum objects and even harbor insects and mold.
Particulate pollution—the “dust” in the air around us—can be generated by industrial emissions, vehicle exhaust, construction soil, mold, wear and tear of fabrics, etc. It is drawn into a building through natural ventilation and the environmental control systems. It is also generated by the day-to-day activities of the museum, such as visitor traffic and exhibit construction. Particulate matter is therefore a complex mixture, often including airborne soil, carbon soot, textile fibers, microorganisms, and protein materials. This combination can be very damaging to collection objects since it is abrasive, attracts moisture, and encourages insects, fungi, and mold.
Chemical contaminants in a museum also originate from both external and internal sources. Sulfur and nitrogen oxides, hydrogen sulfide, chlorine compounds, and ozone are some of the potentially harmful chemical pollutants commonly found in the exterior environment. Within the museum, construction and design materials may emit chemical vapors such as formaldehyde and other volatile organic compounds. These chemical vapors can react with collection objects, causing corrosion…[Any problems from chemicals used for cleaning or pesticides?]
Strategies to reduce pollutants must prevent pollutants entering the museum from the outside environment and eliminate sources of pollutants within the museum itself. A variety of tools is available: hardware and controls that filter the air; design strategies that prevent the build-up of pollutants and avoid use of polluting materials; and museum policies that reduce pollutants within the museum environment.
Elevated or fluctuating relative humidity and temperature can interact with pollutants to exacerbate their ill effect on object health. Therefore, efforts to control pollutants must include management of relative humidity and temperature. Utilizing the appropriate hardware in the design of the exhibit space is an important strategy for moderating pollutants, RH and temperature.
Best Practice: 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?
|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)|