3　Classification of Locations against Lightning

3.0.1　Various locations in petrochemical plant shall be classified into industrial building or outdoor unit based on environment conditions where explosive gas mixture may be formed and the dispersing conditions for gas contained in space.

3.0.2　Semi-enclosed industrial building and opened industrial building shall be classified into industrial building or outdoor unit based on their openness degrees.Large-size compressor building that is provided with roof but its walls are opened shall be classified as industrial building，while the structure where a fewer pieces of equipment and pipes are installed shall be classified as outdoor unit.