A rigorous treatment of risk
requires an accurate definition
that allows its quantification.
A definition that meets these requirements
and that is used by many professionals
is given by the International Atomic Energy Agency.
Basically, what it says
is that the risk can be defined
based on the probability of an scenario
or succession of events
to occur and also,
the measure of the consequence
or damage of that scenario
or sequence of events.
So we can state that safety
is not an absolute concept,
nothing is completely safe.
So we could think
that by answering the question:
Is it safe?
We'll also be answering the question:
How much safe is it?
And that's not true.
A system
could be safe,
but we cannot know
how much safe it is.
Because it depends on many different concepts.
So when we are speaking,
or when we speak of risk,
we will always take into account
the definition formula.
Based on that, a dangerous event,
one which can cause a higher damage,
may not be very risky
because there is a low probability for it to happen.
This is the case of nuclear power plants in general.
So let's see an example.
We can say that a dangerous event
could be considered a minor risk.
For example,
a meteorite falling over your couch
could be very dangerous,
but it's highly unlikely to happen
So the risk could be very low,
and you can feel safe.