There are times when a player performs actions when it is not their turn, such as fighting in a close assault for example. It may also be convenient to interrupt a player's turn because of some event occurring like a booby trap being triggered. The thing to remember is that after the interruption the turn sequence always continues as normal.
Exceptions
Source: Core Rulebook 3E, p. 41
Covers actions that happen outside a player's own turn, such as close assault fighting or interrupting events, after which the turn sequence continues as normal.