Dependency Modelling for Cultural Heritage Joel Taylor, Nigel Blades and May Cassar CENTRE FOR SUSTAINABLE HERITAGE

Undesirable Events: Gare de Montparnasse, Paris, 1895 Late train travelled fast to make up time, so air brakes were required to stop before the terminal. The locomotive brakes were insufficient and the air brakes failed. The conductor was pre-occupied with paperwork and didn’t apply the handbrake. Terminal barrier and 30m of station were insufficient to stop the train.

Risk Chain release exposure attackconsequence Risk assessment Dosimetry Condition assessment Environmental monitoring Part of this is determining which points are critical for hazards to have an effect on a collection There are various ways of assessing and mitigating damage which relate to different stages of the process

Dependencies in Risk Outcomes are dependent on a series of prior events, which can be generalised. What needs to take place for damage to happen? What are the critical points and pathways in this chain of events?

These are deductive, top-down methods of analysing risks in system design. It involves specifying a ‘top event’ to analyse (damage). Then identifying all of the elements in the system that could cause the ‘top event’ to occur. Dependency Modelling

Its Application Concept was developed by Bell Telephones in 1962, as a way of detecting weak points in systems, then adopted and then improved by Boeing. Although originally used to assess system reliability, it is now applied to many things. Requires an understanding of the relationships in the system (boundary conditions).

Damage to object from pollution Exposed surfaces for deposition Interaction of pollutant with collection Presence of pollutant in building No attractive deposition surfaces Generation of pollutant internally Infiltration through natural ventilation AND OR Infiltration through HVAC An example

Relationships in the Model In a positively phrased dependency model, AND dependencies are points of weakness because all events need to occur for the higher event to take place. OR dependencies represent points of strength, because of alternatives options. Can turn these into ANDs through investigation. Probabilities can be applied to each event, so cost effectiveness and efficiency can be determined for any action.

Modelling Deterministic Risk Events often about extent of impact, not presence or absence of impact. Deterministic risks do not rely on specific events, so cannot be modelled this way. The threshold levels can be used to create ‘steps’ for each event, so pathway has defined levels, e.g. presence is NO 2 at 10 ppb, rather than 5ppb.

Deposition rate affected by Temp and RH Damage to objects from 5ppb NO 2 over one year Presence of pollutant in cases Presence of NO 2 in gallery Objects in case Infiltration from outside Internal generation Intake filtration Poor seals in cases External presence of NO 2 Intake position HVAC filter Cellulose nitrate breakdown Unflued heating appliance Reaction from NO 2 No attractive deposition surfaces Presence of NO 2 in building AND OR

Deposition rate affected by Temp and RH Damage to objects from 5ppb NO 2 over one year Presence of pollutant in cases Presence of NO 2 in gallery Objects in case Infiltration from outside Poor seals in cases External presence of NO 2 Intake position No attractive deposition surfaces Presence of NO 2 in building AND Building displaying objects AND

Cultural Heritage Applications The most cost effective approach to mitigating a hazard can be determined. Can be reversed to assess reliability of proposed mitigation method. Can be applied to moveable and immoveable heritage.

Developing the Models Events can be classified ‘top’, ‘intermediate’, ‘undeveloped’ and ‘initiating’. Can develop templates for different risks. Can apply the synergistic effect of risks to dependency model. Can vary top events, and therefore relate to tangible or intangible issues.

Thank You MASTER Project Partners Peter McLennan, UCL Barry Holt, National Safety Council (Europe) European Commission You