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DEFENCE IN DEPTH
Defence in depth: facilities

THE BASIC RATING

 

If we know the potential size of the accident and we know how many safety layers remain, how do we establish the basic rating?

The answer is shown in the table below. The actual table is on page 111 of the Manual. Look at it now and you will see that the basis for the rating is fairly obvious.

One remaining layer gives the maximum defence in depth rating, which of course depends on the maximum potential consequences.

reveal all ratings for this table.

Number of remaining
safety layers

Maximum potential consequences

(1)
Level
5, 6, 7

(2)
Level
3, 4

(3)
Level
2 or 1

A

More than 3

B

3

C

2

D

1 or 0