AIC's 42nd Annual Meeting

Three decades of experience striving to set sensible environmental specifications, and responding usefully to out of specification incidents, was accompanied by confusion and frustration. Through that time learning to see HVAC specifications and deviations through a risk analysis lens led to recognizing three kinds of issues. Understanding the differing natures of decision processes related to those three kinds of issue reduced both confusion and frustration. Two issues, set points and fluctuations, are recognized in relevant standards such as ASHRAE 2012 and PAS198:2012. However, a third kind of issue, excursions to extremes, has neither been incorporated into existing standards, nor brought into our general way of thinking about environmental risk to collections.

The January 1998 ice storm affecting Ontario, Québec and New England resulted in a three-day interruption of electrical power at the Canadian Museum of Nature collection holding facility now known as the Natural Heritage Center (NHC). This resulted in a large upward excursion in temperature in a cool storage facility holding large pelts. In the early summer of 2002, the NHC experienced a single 12-hour excursion to 100% RH.

The latter event was an exceedingly rare, hopefully unique events, brought on by an extraordinary alignment of conditions and operational failures. Nevertheless, recognizing the reality of these sorts of HVAC failures leading to what are termed here as “excursions to extremes” not only makes our understanding of environmental risks to collections more complete, but also sheds light on how we should best think about assessing and managing the other two issues: set points and fluctuations.
Excursions to extremes are easily seen as risk events for which combinations of likelihood and severity of expected events can be calculated through established risk analysis methods. In contrast, set point or annual average T and RH, or more precisely Time Weighed Preservation Index (TWPI), can equally be seen as a an opportunity for increasing a “good” (preservation) or decreasing a “harm” (deterioration). Which reference frame is adopted may depend on the decision context. Fluctuations, or repeated deviations within or beyond specifications, are intermediate in frequency between the continual (or seasonal) issue of set point and the issues of rare excursions to extremes.

Fluctuations can be managed as a “good”, in which case avoidance of fluctuations is the good and more avoidance is better. Adopting this choice is equivalent to adopting the precautionary principle whereby anything that conceivably could cause damage should be managed as if it will cause the perceived damage, until such time as there is clear proof that there is no danger of damage. Alternatively, fluctuations can be managed as a “harm” to be avoided. In this case, an understanding of the vulnerability of a collection to a given T or RH deviation, or pattern of deviations, is required to assess and manage the risk they pose.