Dependency modelling for cultural heritage

CENTRE FOR SUSTAINABLE HERITAGE
Dependency Modelling
for Cultural Heritage
Joel Taylor, Nigel Blades
and May Cassar
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
assessment
Risk Chain
Environmental
monitoring
Dosimetry
release
Condition
assessment
exposure
attack
consequence
There are various ways of assessing and mitigating
damage which relate to different stages of the process
Part of this is determining which points are critical
for hazards to have an effect on a collection
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?
Dependency Modelling
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.
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
An example
Interaction of
pollutant with
collection
No attractive
deposition
surfaces
AND
AND
Exposed
surfaces for
deposition
Presence of
pollutant in
building
OR
Generation of
pollutant
internally
Infiltration
through
natural
ventilation
Infiltration
through
HVAC
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.
Damage to objects from 5ppb NO2 over one year
Deposition rate
affected by Temp
and RH
Presence of
pollutant in cases
AND
Poor seals
in cases
Presence of
NO2 in building
Objects
in case
Presence of
NO2 in gallery
No attractive
deposition
surfaces
AND
OR
Infiltration
from outside
Internal
generation
AND
OR
External
presence
of NO2
Intake
filtration
Intake
position
OR
HVAC
filter
Reaction
from NO2
Unflued
heating
appliance
Cellulose
nitrate
breakdown
Damage to objects from 5ppb NO2 over one year
Deposition rate
affected by Temp
and RH
Presence of
pollutant in cases
Poor seals
in cases
AND
Presence of
NO2 in building
AND
Infiltration
from outside
AND
External
presence
of NO2
Intake
position
Objects
in case
Presence of
NO2 in gallery
AND
Building
displaying
objects
No attractive
deposition
surfaces
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