Environmental monitoring standards
Environmental monitoring standards? Which standards?
Environmental monitoring standards for collection environments are a series of targets for factors such as relative humidity, temperature, light, pollutants, and pests. The targets, sometimes referred to as “ideal conditions”, are followed to avoid damage or to slow the rate of deterioration to collections.
The development and agreement of environmental standards, particularly when talking about temperature and relative humidity, has been a process that is still evolving and changing.
For this reason, it’s important to clarify how many standards are available and what the current guidance for collection care is. Let’s begin with some historical context to get a better picture about the most recent debates about this topic.
The Rise and Fall of the 50/70 for environmental monitoring standards in museums
The early 20th century saw the beginning of preservation research in humidification and environmental monitoring and control for the benefit of collections. During the first 20 years of the century, the MFA Boston had determined preservation was enhanced between 50-55% RH (except for metals), and many museums in the U.S. were opting to keep temperatures low (55°F) to decrease organic rates of deterioration (Sturgis, 1905).
By the 1930s, 60°F/60% RH were more widespread, but wartime restrictions in the 1940s relaxed these numbers to wider ranges (50-70°F and 55-65% RH). Note how global events and interests affect and relax our standards for environmental standard targets (Coremans, 1936).
Harold Plenderleith’s research in the UK in the 1960s revealed a common use of 50-60% RH in museums. He set a range of acceptable limits between 50-65% to avoid cracking thin wooden panels below that and risk of mold above it. A temperature range of between 60-75°F is suggested, but mostly for human comfort. The numbers vary back and forth in that general region during the 60s and 70s until The Museum Environment, by Garry Thomson, is published in 1978.
The Museum Environment was one of the first publications dedicated entirely to the management of the environmental conditions for museum collections. Thomson established two types of control, Class 1 and Class 2.
Class 1 applied to major national museums, old or new, and all important new museum buildings. Class 2 was intended to avoid major dangers while keeping costs and building alterations to a minimum, for example, historic houses and churches.
Thomson’s Class 1, is referred to as the “50/70” rule: 50% relative humidity (plus or minus 5 degrees) and 70 degrees Fahrenheit (plus or minus two degrees).
Despite Thomson’s warning to take his numbers as guidelines more than rules, the Class 1 “50/70” target appeared as a magic number that many museum professionals were seeking. For years, many museums and even international committees for standardization used the 50/70 rule to establish parameters for environmental control.
Letting go of standards and “best practices”
The 50/70 standard became widely known in guidelines, conservation literature, and conservation education, but proved to be problematic for historic structures, museums in different climates, and small museums with limited budgets. Trying to maintain 70°F degrees and 50% relative humidity year-round posed challenges and risks for many structures, requiring a high investment to install, run, and maintain HVAC systems.
Additional research in the 1990s proved that the single 50/70 standard was not suitable for all institutions, nor for all types of materials in museum collections.
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) added a chapter for museums, galleries, archives and libraries to their application handbook in 1999. The chapter is mainly directed at engineers or facility staff responsible for HVAC systems working for cultural institutions.
ASHRAE continued to revise their guidelines over time. The approach in their latest version (2019) abandons any single universal standards and emphasizes risk management approaches that take into account the sensitivity of collections, energy costs, and architectural settings. It also “presents best practices and advice on planning, designing and implementing environmental strategies” (ASHRAE, 2019) for the preservation of heritage culture collections safeguarded in buildings.
In 2010, the Boston Roundtable issued another set of recommendations in their report, “Rethinking the Museum Climate.” The report proposed that a setpoint in the range of 45-55% RH with an allowable drift of +/-5%, yielding a total annual range of 40% minimum – 60% maximum, and a temperature range of 59-77˚F was acceptable for the majority of cultural materials.
Jumping into the 21st century, ongoing conversations about the demanding costs of running HVAC systems has led to the publication of documents advocating for sustainable management of collection environments.
Another document published in 2014, was the IIC and ICOM-CC Declaration – Environmental Guidelines. The 50/70 rule was challenged around the globe by the AICCM and the AIC who also published new interim guidelines for loan conditions.
In 2015, a group of leading museums around the world agreed to and published the Bizot Green Protocol – a set of environmental guidelines for loans with a temperature range of 16-25˚C (59-77˚F) and a humidity range of 40-60%RH with fluctuations of no more than ±10% RH per 24 hours.
Environmental requirements for collections today
Global events are having a huge effect on expectations about environmental standards today. The current financial challenges and the climate crisis are calling for a net zero strategy for all industries. This means cutting greenhouse gas emissions to as close as zero as possible. In the collections world, this will affect our use of HVAC systems, transportation for exhibits and loans, and materials chosen for conservation treatments, exhibitions, and storage.
Many institutions are exploring different strategies to cut down energy costs by reducing the use of HVAC systems, using passive strategies, and establishing targets for environmental conditions based on a risk management approach and using environmental guidelines as a looser reference point.
However, in real practice, environmental requirements for loaned artworks continue to be narrow and stringent, requiring the constant use of HVAC systems to reduce any risk of damage from incorrect temperature and incorrect temperature at any cost, ignoring a holistic analysis of risks.
Currently, environmental targets included in loan agreements are causing a snowball effect where institutions of all sizes try to keep a good reputation, holding onto tight parameters to avoid the risk of losing trust and credibility.
What does this mean for preservation professionals today?
It is not uncommon to mention certain targets for temperature and relative humidity, as you will see in some of the chapters in this guide, because there is a good amount of research that shows how certain conditions can be damaging for certain materials. However, any environmental strategy needs to be built within the context of each institution, because a one-size-fits-all approach may not be the best choice for your building or your collection.
Today, the best practice in collection care is to follow a risk management approach considering all the risks of damage for your collection.
Aspects to consider:
- the local climate and environmental conditions of the area where your institution is located
- the type of building that houses your collection
- the environmental control system
- your budget to maintain any type of control
- the types of materials in your collection
- Additional consideration for objects or materials that are more vulnerable than the rest of your general collection.
At the international level, there is a growing recognition that the Global South does not need to conform to standards set elsewhere without taking into account local climates and available resources. See, for example, the themes for the International Institute for Conservation of Historic and Artistic Works 2024 Lima Congress.
The move towards passive environmental controls and less prescriptive standards will allow preservation professionals around the world to determine the most appropriate levels of environmental control and management for their own situations.
American Society of Heating Refrigerating and Air-Conditioning Engineers. “Chapter 24: Museums, Galleries, Archives, and Libraries.” In ASHRAE Handbook: HVAC Applications, 2019.
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Australian Institute for the Conservation of Cultural Material (AICCM). “Environmental guidelines for loans – finding a way forward.” In AICCM National Newsletter No 147 September 2019.
Bizot Green protocol, 2015
Coremans, P. “Air conditioning in museums.” Museums Journal. 36 (November, 1936): 341.
Environmental guidelines (2020) Conservation Wiki – A collaborative knowledge resource. (Accessed: 03 May 2023).
Hatchfield, P. 2011. Crack Warp Shrink Flake. Museum, January/February.
Icon. “Environmental Standards – Embracing Risk.” ICON, 25 Apr. 2023
IIC and ICOM-CC Declaration – Environmental Guidelines
Sturgis, R. Clipston. Report on Plans Presented to the Building Committee. Museum of Fine Arts, Boston, 1905: 51
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10 Ways Museums Can Be More Sustainable
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