TSA Insight Magazine Issue 7 - Magazine - Page 12
RISK AND
TOLERABILITY
CRITERIA: ARE WE
C O M PA R I N G A P P L E S
AND PEARS?
total risk based on the number
of people affected and the
frequency of the relevant events
isk is a somewhat
and is often used as a synonym for
nebular concept,
societal or group risk. That might
particularly
in
be risk of a single scenario or
the context of
multiple hazards. Individual risk,
major accidents.
on the other hand, considers the
Although we are often driven
total risk to a single person from
to try to make it as precise as
all hazards on an establishment.
possible, there are inevitably
Risk assessments can calculate
a
assumptions
various forms of risk, so we need
required to narrow down the
to be clear what the number
inputs to a single number. A lot
generated really is.
of things are dependent on the
HSE guidance such as ‘Reducing
outcome of risk assessment;
Risks, Protecting People - HSE’s
without it we run the risk of
decision-making process’ (R2P2)
neglecting to manage our more
is helpful in providing tolerability
significant hazards, and so it is
criteria for individual risk, often
important to appreciate where
referred to as the ALARP triangle,
the assessment comes from
however there is less clarity for
and to understand the results.
societal risk.
How risk is presented plays a
An F-N graph can be developed
vital role in how it is perceived
to illustrate criteria for societal
and managed, but how can
risk using HSE’s guidance in their
we make such an intangible
‘Guidance on ALARP Decisions
concept into something more
in COMAH’ document. The F-N
material?
graph allows the cumulative
R
How risk is
presented plays a
vital role in how it
is perceived and
managed, but
how can we make
such an intangible
concept into
something more
material?
Aggregated risk determines the
number
of
frequency
events
at
an
Tolerability as a driver
establishment per year (F) to
One driver for presenting risk as
be plotted against the number
a single number is to compare
of fatalities from all events
that
tolerability
assessed (N), allowing for the
The first factor that
position of the assessed risk
should be considered when
against the societal risk criteria
presenting the outcomes of a
to be presented.
risk assessment in this way is a
It is important to consider that
clear understanding of what is
the risk criteria provided by
being assessed or calculated.
the UK regulator are intended
number
criteria.
12
of
I N S I G H T
to
M AG AZ I N E
