Indoor air pollutants

While temperature, relative humidity, and light have long been major concerns in passive conservation, indoor air pollution has become another recognized factor. The term “carbonyl pollution,” as used in this field, refers to indoor air pollutants such as acetic acid, formic acid, and formaldehyde. Many institutes are concerned with carbonyl pollution-induced deterioration and are performing air-sampling and materials-testing experiments. Unfortunately, the results of such studies are rarely published. Without access to the results, it is difficult to determine the current state of carbonyl-pollution research.

A conference entitled “Museum Pollution: Detection and Mitigation of Carbonyls” was held at Strathclyde University in Glasgow in 1998. More than 30 delegates from the United Kingdom, the Netherlands, Denmark, Canada, and the United States attended. The following recommendations were made:

  • Construct a database to collate data from past and future sampling experiments on the relationship between carbonyl pollutant concentration and artifact damage.
  • Construct a database to collate information on materials that have been judged as safe for short- and long-term use in proximity to susceptible artifacts.
  • Develop standard operating protocols for acid and aldehyde vapor testing in museums and other storage areas.
  • Form a working group of conservators and scientists, the Indoor Air Pollution Working Group (IAP), to be coordinated by the NICH.

As a follow-up to the 1998 meeting, a second symposium was held at the NICH in August 1999. The symposium, “Indoor Air Pollution: Detection and Prevention,” was organized by the IAP Working Group that had been initiated at the 1998 meeting. The primary objectives of the meeting were to exchange information and discuss current research on indoor air-pollution-related problems. The following recommendations were made:

  • Air-sampling techniques. Laboratories that perform air sampling and analyses should compare their protocols, identify differences, discuss the rationale behind choices, and develop a common protocol.
  • Understanding pollutionartifact interactions. A consensus must be established with respect to pollution levels and material damage. The Getty Conservation Institute (Los Angeles, California, USA) is willing to fund the construction of a database that could be used to compile sampling data from field and laboratory measurements.
  • Materials testing. Four types of materials tests are commonly used: (1) qualitative total corrosivity; (2) qualitative specific corrosivity; (3) quantitative total corrosivity; and (4) quantitative specific corrosivity. A format for a materials-testing list is proposed; it should be based on the experience of the National Museum of Scotland.
  • Dissemination of information. To raise awareness for indoor air-pollution problems in preservation, the discussions in the working group should be disseminated. Several actions have already been undertaken: the postprints of the 1999 meeting have been published in hard copy (Brokerhof and Gibson 2000), electronic versions of the postprints are available from the NICH Web site (, and Morten Ryhl-Svendsen (School of Conservation, Copenhagen, Denmark) has constructed a Web site that offers additional information on indoor air quality (


Controlled-atmosphere fumigation and thermal treatments

Over the past 10 years, the use of chemical methods for pest control has been replaced to a large extent by the use of nonchemical methods. The emphasis now is on the use of modified atmospheres (MA) and controlled atmospheres (CA).

Tom Strang from the CCI is quantifying the effects of controlled-atmosphere fumigation (carbon dioxide, nitrogen, or argon) and thermal treatments (low-temperature or high-temperature) (Strang 1998).

Disinfection with essential oils

The antimicrobial properties of essential oils have been known since antiquity, but it was not until the nineteenth century that these substances were analyzed.

The study of the antifungal activity of these oils is more recent. Malalanirina Rakotonirainy, Marie-Ange Raisson, and Françoise Flieder from the CRCDG are studying the characteristics of essential oils. They are seeking to develop ways in which to apply them to prevent fungal growth on cultural properties and in storage areas, as well as to treat objects that are already infected.

The fungistatic and fungicidal activity of six essential oils (bay, wormseed, citronella, eucalyptus, super lavender, and sage) was examined on several fungal strains chosen from those most frequently found in libraries, archives, and museums. The effectiveness of the oils was studied in relation to their composition. All six oils revealed antifungal properties, although the results varied. It is unclear, from the preliminary findings, how practical the use of essential oils will be because of the large concentrations required for disinfection (Rakotonirainy et al 1998).

Flexible fumigation enclosures

Fumigation chambers have always been used in conservation practice to treat objects infested with pests; however, these chambers are expensive to construct, and not all institutions can afford them. An English company, Rentokil, has developed a reusable and flexible fumigation enclosure, the Rentokil Bubble. This portable enclosure is designed for use with methyl bromide, phosphine, or carbon dioxide. For the use of nitrogen, the company designed a different line of fumigation enclosures that have a heat-sealable, aluminized barrier film. These bags are not intended for reuse.

Two researchers at the Getty Conservation Institute (Los Angeles, California, USA), Kerstin Elert and Shin Maekawa, tested the enclosures for nitrogen fumigation. The two bubbles, 35 m2 and 6 m2, were investigated for both the oxygen-transmission characteristics of the materials and for the gas-tightness of the enclosure. The tests showed varied results but clearly confirmed the suitability of the bubbles for anoxia treatment. Some practical limitations, especially concerning the size of the units, were, however, detected (Elert and Maekawa 1997).

High-temperature treatment

High-temperature treatment has been proved to be effective in exterminating insects in collection materials. Tom Strang from the CCI designed a bag that will allow solar heating of the contents (slightly in excess of 40C) in such a way that thermal deinfestation of the bag contents will be achieved. A prototype has shown the idea to be feasible, but additional tests need to be carried out.

Oxygen reduction and pest control

It is possible to control insect infestation by reducing oxygen concentration, a form of modified atmosphere. Oxygen reduction is increasingly regarded as a recommendable alternative to insecticides and pesticides, which are harmful to human health, pollute the indoor environment of conservation institutes, and may even produce reactions with the objects in the collection.

In 1998, the European Union financed a project called “SAVE ART.” Its purpose is to control pests by reducing the oxygen concentration of the environment through the use of an electromechanical nitrogen generator (the VELOXY [VEry Low OXYgen] system). The idea is simple but effective: the oxygen in the air surrounding the object is removed (replaced by nitrogen) until a residual concentration of 0.1 percent to 0.2 percent is reached, at which level all insects will be killed.

The following parties are involved in the project:
Italy: Resource Group Integrator S.r.l. (coordinate project and produce equipment), MASTER S.r.l. (produce equipment), Istituto Centrale per la Patologia del Libro (test prototype);
United Kingdom: Central Science Laboratory (test effectiveness);
Spain: Consejo Superior de Investigaciones Biologicas (test effectiveness);
Sweden: Swedish Museum of Natural History, PRE-MAL.

Realscale validations of the VELOXY system were performed atthe National Marciana Library (Venice, Italy), El Prado Museum and Centro de la Restauracion del Mueble (Madrid, Spain), the Swedish Museum of Natural History (Stockholm, Sweden), and the National Museum of Wales (Cardiff, UK). The real-scale tests showed promising results. Since the project’s inception, 12 VELOXY systems have been assembled and are now operative at several museums, libraries, and archives (Conyers, in press; Gialdi 1998).

PRE-MAL is part of the European SAVE ART project. The investigations include testing the effects of pest-control methods on pest insects, artifacts, and humans. The effects of long-term storage in a low-oxygen atmosphere are tested on various materials (Åkerlund 1998; Åkerlund et al 1998; Antonsson and Samuelsson 1996; Bergh et al 1996; Bergh 1998; Björdal 1998; Kolmodin-Hedman and Flato 1998; Petersson 1998).

The following institutions are involved:
Sweden: National Museum of Science and Technology (coordinator), Skokloster Castle (test treatment on pest-infested saddles), Swedish National Testing and Research Institute (test freezing method), Karolinska Institute, Department of Occupational Health (test health personnel), Swedish University of Agricultural Sciences, Department of Environmental Assessment (test health personnel);
Denmark:Technical University of Denmark, Department of Biotechnology (test effectiveness of treatments).

Oxygen-scavenging cell

A modern way to slow the deterioration of organic objects is to minimize the oxygen content of the environment. Mark Gilberg from the National Center for Preservation Technology and Training (Natchitoches, Louisiana, USA) and David W. Grattan from the CCI investigated a prototype of an electrochemical cell and its ability to reduce the oxygen concentration in a small chamber that is similar to a museum display case.

The oxygen-scavenging cell is capable of removing oxygen from enclosed spaces, even in the presence of high leak rates; however, the reduction rate is slow. The most significant drawback is the high relative humidity that develops in the chamber. The system needs to be modified to allow better control (Gilberg and Grattan 1996).


Climate conditions and standards

The control of RH continues to be an expensive and difficult challenge. In many situations, an attractive option is to control the RH within display cases instead of controlling the entire space.

Stefan Michalski, Paul Marcon, and Tom Strang from the Canadian Conservation Institute are working on a centralized module supplying filtered and humidity-controlled air to each case through small tubes (typically 6-mm diameter) without return air, relying on compensating leakage from the case. The possibility of using an Internet application to provide remote control of the module and remote monitoring of the units is being investigated.

The control of temperature and relative humidity is generally accepted as a means to prevent degradation of collections. Several guidelines are being developed, but the rationale behind these standards is not always clear.

Stefan Michalski from the CCI looked more closely at the basis of these standards and the costs of achieving them. In cooperation with the Canadian Council of Archives, the CCI created a document entitled Environmental Guidelines for Canadian Archives. Parts of the work have been summarized in the new chapter for engineers in Museums, Libraries and Archives in the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) Handbook, Applications Volume, 1999 (Michalski 1998, 1999; Michalski, in press).

Determining safe ranges for the storage climate of paper and other artifacts and understanding how temperature and relative humidity conditions within this range affect the rate of changes over time are two objectives of research conducted by David Erhardt and co-workers from the Smithsonian Institution, Smithsonian Center for Materials Research and Education. Changes over time in properties such as stiffness, strength, and elasticity were examined using both naturally aged samples and accelerated-aging tests. Results demonstrated that the rate and nature of chemical degradation processes as a function of environmental conditions are correlated with the changes in physical properties taking place in the constituent materials. On the basis of the findings, several recommendations with regard to environmental conditions were made. The research report also discusses critically some common perceptions, especially with regard to the relative humidity conditions (Erhardt et al 1999).

Lighting technique and guidelines

In the last decade, conservation scientists have given increased attention to lighting issues, particularly the damaging effects of light on artifacts. Two processes are responsible for this damage: photochemical action, which causes fading, chalking, and loss of strength; and radiant heating, which causes surface cracking and embrittlement.

In 1997, the Preservation Technology and Training Project marked significant progress toward a solution to this long-standing problem. Christopher Cuttle from Rensselaer Polytechnic Institute (Troy, New York, USA) examined an innovative lighting technique that promises to reduce rates of light-induced damage without affecting viewing satisfaction. Cuttle recorded individual, subjective evaluations of works of art displayed under different lighting conditions.

The studies suggest that light concentrated in three spectral bands (with center wavelengths of 450, 530, and 610 nm) could provide levels of illumination equal to standard broad-spectrum lighting with substantially reduced levels of damaging incident radiant energy. Three-band lighting could allow the display of artifacts for longer periods than is possible with traditional illumination sources (Cuttle 1998).

Standard light levels have been introduced over the past 30 years. Although the intent of such standards is clear, their application to broad ranges of object types has been somewhat arbitrary. Resolving the issue of visibility versus vulnerability of the object has been difficult for the preservation community.

Stefan Michalski from the CCI has been working with a technical committee of the International Commission on Lighting to develop an improved lighting guide. This guide recommends steps to ensure safe lighting of displays, including the classification of all exhibits according to a four-category scale, determination of the acceptable level of UV radiation, calculation of the annual exposures, and planning for the maximum duration of the display, both for the exhibition and for individual objects (Michalski 1997).

The main objective of a current project of the State Central Archives in Prague (Czech Republic) is the development of guidelines for the protection of all sorts of archival and library materials from the damaging effects of light during exhibitions. The planned studies include investigation into the influence of visible and UV light on the mechanical, chemical, and optical properties of paper and other materials, and into the lifetime and effectiveness of UV filters (Durovic 2000).

Materials testing program

The NARA Document Conservation Laboratory (College Park, Maryland, USA) maintains a testing program to ensure that proposed exhibit and storage materials do not cause damage to permanent records. All the tested products are listed on NARA’s Web site ( Inclusion in the list does not imply that a product is acceptable, only that it has been tested. The conservator, on basis of these results, can decide whether or not it is safe to use the particular material. In general, the laboratory uses the Oddy and photographic activity tests (PATs). However, since 1996, A-D strips, which were developed to test for film deterioration, also have been used as a quick check on whether any acidic volatiles are being emitted by the material in question. The results apply only to the specific samples tested at a given time. Each run of paper, board, plastic, or other material from a given mill or manufacturer can, and probably will, be different. Therefore, the testresults may not apply to products ordered today from the same vendors. Exclusion of the testing program merely implies that the manufacturer did not bid, did not supply samples, or was not asked to supply samples.

Polyethylene foam

Polyethylene foam is used today for storing all kinds of objects. Since the ban on CFC agents, drastic alterations have been made in the production of polyethylene foam. Alarming reports from several institutions indicated the urgent need to investigate the aging behavior of the new foam products.

Scott Williams from the CCI is studying the effect of the changes in the polyethylene foam manufacturing processes and formulations in relation to the deterioration mechanism of the foam products. Degraded samples will be chemically examined, and undegraded samples will be subjected to accelerated aging and subsequent analysis (Williams 1998).