JEAN TÉTREAULT

The Canadian Conservation Institute

STANDARDS FOR LEVELS OF INDOOR POLLUTANTS IN MUSEUMS

Standards for maximum acceptable levels of outdoor pollutants have been in place for more than 20 years. Gary Thomson, in his first edition of 'The Museum Environment', used these standards (based on typical clean outdoor levels) to establish maximum acceptable levels of the pollutants for museum collections (10 µg m^-3 for SO₂, and NO_x, and 2 µg m^-3 for O₃). The National Research Council (US) and the American National Standards Institute base their standards on the use of HVAC technology. In most cases, values have been established for outdoor pollutants based on this last approach (5 µg m^-3 for SO₂, NO_x, and 25 µg m^-3 for O₃). Heritage institutes and archives are usually aware of these standards, and make serious efforts to ensure they are enforced.

Before the mid-1980's, indoor (generated) pollutants received little attention from museum managers and engineers. The most common method used to establish allowable levels of indoor pollutants such as carbonyl compounds was to use 'the best control technology'. Based on this statement, HVAC systems were sometimes upgraded with activated charcoal or potassium permanganate filters. However, the main source of indoor pollutants is the display and storage materials used in the vicinity of artefacts. These are normally small airtight enclosures. Therefore, the use of HVAC systems is an inappropriate control system in this instance. Since the display and storage materials themselves directly influence the indoor pollution level it is important that standards for maximum allowable levels are established and implemented.

At present, maximum acceptable levels of indoor pollutants can be based on their clean outdoor environment level (about 1 - 10 µg m^-3 for most carbonyls). This approach is simple and avoids controversy on thresholds and usage of best control technologies. As new experimental evidence is compiled, this standard can be revised.

Setting maximum levels for indoor pollutants to outdoor levels should not deter those who prefer 'artificially cleaner' levels for their museums. For those who cannot achieve the acceptable levels for outdoor/indoor pollutants for logistic or financial reasons, information on the known potential damage to specific artefacts can help assess the risk.

CCI is in favour of standardising allowable levels of indoor pollutants. The levels could be set by consensus of a number of different institutes. A harmonisation of both indoor and outdoor pollutant recommendations will be suitable. Setting such standards would 1) stimulate research to extend the knowledge of potential damage to artefacts by pollutants, 2) encourage the development of analytical techniques to find the optimal levels of pollutants and 3) aid in the development of specifications for display, storage and transportation of materials.

Systematic Approach for Indoor (Generated) Pollutants
TO AVOID (better than dealing with the problem):

• Establish standard levels
• Determine the artefact's sensibility and mechanism of deterioration for each pollutant
• Establish a database of 'safe' materials that can be used in museums
• Develop specifications for enclosures (based on standard methods)

TO BLOCK (deal with emission rate, concentration, damage rate, total damage on objects):

• Block emissions with barrier film (either apply to the source material or the artefact)
• Block infiltration (by absorption, adsorption or chemical reaction)
• Use scavengers (competitive)
• Ventilate by dispersion, positive (clean air) pressure
• Reduce the amount of other reactants, catalysts, radiation
• Reduce the temperature
• Reduce the exposure time

ADDITIONAL NOTES