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.

Control particulate matter through a combination of macro and micro solutions, including enclosing sensitive objects and providing adequate air filtration. When infiltration of particulate matter is appropriately controlled, the aestheic of the display is enhanced and the need for cleaning/exhibit maintenance is reduced.

General Guidelines

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.

Macro Solutions

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.

Micro Solutions

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

[Placeholder introduction]
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.

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.

What design strategies help decrease object damage from particulates and chemical pollutants?

Using exhibit cases:

A case provides the optimum level of protection for objects that are susceptible to damage from dust and pollutants.

• Air filters should be incorporated in ventilated case designs or the exhibit case should be sealed sufficiently to restrict airflow and prevent particulates being drawn inside.
• Pollutant absorbent materials, such as charcoal or potassium permanganate, can protect sensitive objects from chemical contaminants.

Using object-safe materials in the exhibit:

• Use materials that are chemically stable and do not offgas in the exhibit area and especially in close proximity to exhibit objects. There are many construction materials and furnishings—for example, plywood, particle board, synthetic carpeting, adhesives and paints—that can bring contaminants and pollutants directly into the exhibit area. Such materials can off-gas corrosive vapors or react with nearby materials. [For more information on object-safe materials see Standard *.]
• As an extra precaution, isolate objects from direct contact with exhibit construction material, painted or varnished surfaces:
• Use a chemically neutral layer of film, fabric, or cushioning foam, to separate objects from potentially damaging surfaces, such as paint or varnish. Inert paper, polyethylene, polyester sheeting and foil are acceptable barriers.
• Elevate objects with mounts.
• Avoid organic materials or use with extreme caution. Animal products, wool, feathers, fur, vegetal matter, wood, and preserved foods may introduce molds (as well as pests) into the museum.
• Avoid using dried and friable materials for props and settings. Materials such as thatch, shingles and moss may become brittle, creating dust and debris.
• Use materials that are clean and sterile for props and settings. Dirty materials can introduce dust and debris that will deposit on objects and recirculate through the HVAC system:

Screen and/or wash materials. For example, wash pebbles and sand to remove fine particles, dirt, and insects.

Use materials free of corrosion.

Do not use old materials in poor condition

[For more information on object-safe props see Guideline *]

Creating an exhibit layout that encourages air circulation:

• Provide unrestricted airflow for the heating and air-conditioning systems.
• Provide air space between collections and known pollutant sources since concentrations of pollutants are highest near a contaminant (such as large wooden exhibit panels and platforms).
• Avoid creating pockets of still air in which pollutant levels can concentrate (for example, long runs of cases that extend from floor to ceiling).

Using structural modifications to help seal the exhibit space and exclude contaminants:

• Incorporate a vestibule at the exhibit entrance to control airflow. Install grates to capture dirt from visitor’s shoes.
• Enclose the exhibit area with well-fitting doors.
• Block unnecessary windows and doors with insulating material.
• Limit the infiltration of unfiltered air through cracks and gaps in the building by caulking or gasketing doors and windows to reduce particulate pollution.

Best Practice: Museum policies are instituted to protect objects from particulates and chemical pollutants

What museum practices can assist in protecting objects from particulates and chemical pollutants?

[Placeholder ideas; needs amplification & revision]

• Smoking is prohibited inside the building
• Smoking is prohibited outside the building near air-intake vents
• Windows are kept shut
• Timely repairs are performed on broken windows and on dried putty and caulking around windows and doors to eliminate cracks, which admit dirt
• Housekeeping keeps dust and particulates to a minimum
• Policy of using object-safe materials, whenever possible, throughout museum
• Caution in the use of chemical sprays for cleaning
• Caution in use of chemicals for pest control (For more information on recommended methods of pest control, see STANDARD 20: Preventing Pest Damage).
• Dedicated space is provided for exhibit construction to reduce particulates and pollutants in the exhibit location
• Appropriate training provided to staff to ensure HVAC is functioning correctly, and there is timely renewal of filters and pollutant absorbers.
• Ongoing costs for housekeeping, and for maintenance and renewal of pollution controls and equipment is included in museum’s operating budget.

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)