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

attack consequence

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

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 NO2 at 10 ppb, rather than 5ppb.

Deposition rate affected by Temp

and RH

Damage to objects from 5ppb NO2 over one year

Presence of pollutant in cases

Presence of NO2 in gallery

Objects in case

Infiltration from outside

Internal generation

Intake filtration

Poor seals in cases

External presence

of NO2

Intake position

HVAC filter

Cellulose nitrate

breakdown

Unflued heating

appliance

Reaction from NO2

No attractive deposition surfaces

Presence of NO2 in building

AND

AND

AND OR

OR

OR

Deposition rate affected by Temp

and RH

Damage to objects from 5ppb NO2 over one year

Presence of pollutant in cases

Presence of NO2 in gallery

Objects in case

Infiltration from outside

Poor seals in cases

External presence

of NO2

Intake position

No attractive deposition surfaces

Presence of NO2 in building

AND

AND

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