Objective is to limit the number of possible primary failures occurring in the optical fibre cable in a specified installation to within values which are lower than or equal to the limit value, defined as the tolerable frequency of primary failures.

Gives the method for calculating the possible number of primary failures, choosing the feasible protective measures and indicating the tolerable frequency of primary failures.

Secondary failures are not considered. The tests described in annex G are convenient only for the risk evaluation associated with lightning in fibre optic installations. Tests for the qualification of a cable design are outside the scope of this standard.