Filters for Ventilated Cases
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The air drawn into a deliberately ventilated case should be filtered to remove particulate matter and chemical pollutants.
Why is it necessary to filter the air entering an exhibit case?
Ambient air entering a case can bring dust and pollutants with it. The rate of air passing through an exhibit case is often surprisingly high due to the forces of convection. A relatively large quantity of contaminates can be drawn into the case as interior air is heated, rises and exits through holes and gaps. Control of dust and pollution entry by filtration at case vent holes is particularly important when HVAC filtration is ineffective or non-existent in the room.
How are the vents filtered?
Three filtration methods are commonly used to filter the vent (port) holes. To be successful, it is necessary to filter each port hole in the case.
- Fit a vent with a commercial respirator cartridge and filter: Commercial respirators hold disposable cartridge filters which are screwed onto the respirator. Filters are available for dust and for a wide range of chemicals, including organic solvents, formaldehyde, sulfur pollutants, ozone and acids. Some cartridges allow several filters to be combined. The case must be designed with a fitting to receive the respirator filter (this usually means that a screw-like adapter is installed in the vent hole). The joints between the case wall and the coupler must be well-sealed with caulk sealant or gasketry.
- Cover the vent with a custom fabric or paper filter: Fabrics used to cover a vent must be tightly woven, yet breathable to allow unrestricted air flow. While cotton, linen or a synthetic material may be used, Pacific SilverCloth or Charcoal Cloth are better choices because they have the added benefit of some chemical pollutant filtration. Paper can also be used such as 3M Anti-Tarnish Strips. The fabric or paper can be glued in place with hot-melt adhesive or can be secured through mechanical means such as a screw coupling. The fabric can either be stretched tautly over the port, or a pouch can be created. Such a pouch can contain a reservoir of a pollution absorber, moisture absorber and/or insect repellent.
- Fasten a pre-fabricated air duct filter to the inside of the vent: Cut commercial filters for HVAC systems down to an appropriate size. Use fiberglass or paper filters; pleated filters are usually too difficult to cut and too bulky for use. Choose a high efficiency dust filter, preferably one containing pollution-absorbent products such as activated charcoal or potassium permanganate. The filter is attached in the same manner as the fabric or paper.
Products, Manufacturers, and Suppliers
Mention of a product, manufacturer, or supplier by name here is for information only and does not constitute an endorsement of that product or supplier. Listed materials have been used successfully in past applications. It is suggested that readers also seek alternate product and vendor information to assess the full range of available supplies and equipment.
Respirator Cartridges and Filters
- Available at laboratory supply and safety supply companies; brands such as 3M, North, Survivair, and Willson
Particulate Filters for Air Ducts
- Available at local hardware stores