4.1 In this book, the term “interruptions to laytime” is used to cover those periods when laytime does not run because they are outside the definition of lay-time as expressed in the laytime clause. Excepted periods, on the other hand, are those periods that are within the definition of laytime, but nevertheless excluded by an exceptions clause. The principal difference between the two is that with the latter it is necessary to show a causal connection between what is excepted and the failure to work cargo, whereas with the former all that need be shown for causation is that the excluded state of affairs exists at the place where cargo would have been worked.