Surprises happen anywhere and to anyone. In your operation, you can expect that regardless of your best efforts, some work will arise that must be done right away. Most would call these emergencies.

To me, an emergency is something that is or is about to have a MAJOR impact on: Safety (i.e.: injury or death), Environment (i.e.: a major incident that is likely to get you fined or shut down), or Production/service delivery (i.e.: irreparable impact on the bottom line in the financial reporting period).