There is no such thing as a 'safe period' where conception will not occur - only variable times when conception is less likely that at other times. Sexual contact is a biloigical function, and the odds are very very heavily loaded in favour of conception, because that is the intended outcome. If every sperm in the average emission fertalised one egg, it would re-populate the continent of North America - those are the odds with which you are dealing. If you don't want a pregnancy, don't tamper with nature - you will loose!