Both Plan B pills can be taken at the same time with no decrease in effectiveness or increase in side effects. Plan B should be taken within 5 days (120 hours) of unprotected sex and can reduce the risk of pregnancy up to 89%. But it is more effective the sooner you take it.
A hazard and operability study (or HAZOP) is a systematic, critical examination by a team of the engineering and operating intentions of a process to assess the hazard potential of mal-operation or mal-function of individual items of equipment and the consequential effects on the facility as a whole.
Once the causes and effects of any potential hazards have been established, the system being studied can then be modified to improve its safety. The modified design should then be subject to another HAZOP, to ensure that no new problems have been added. A HAZOP study is a team effort.