Industrial hygiene engineering can be utilized most effectively when it is employed in the design or construction phases of new or modified chemical manufacturing processes. Minimization of leaks, spills, fugitive emissions and other releases is the goal. Some chemical and physical agents can still be released during normal or non-normal operations and during plant turnaround procedures and these require continuous industrial hygiene surveillance. It follows that industrial hygiene principles must continue to be applied in all phases of the petrochemical industry from the beginning of the design and throughout the life of the unit.