The present invention relates to a detector arrangement (10) included in a preventative, protective system. The sensor lobes of at least two sensor units or sensor sections (10a-10g) are arranged to cover the cross-sectional area of a tubular transport device (8). The arrangement includes a unit (16) for evaluating the output signals of the sensor units (10a-10g), and an activation unit (12) which is adapted to evaluate sensed sub-intensities (10a'-10g') relating to wavelength ranges and each deriving from said sensor units (10a-10g), and to thus co-ordinate received wavelength-related and sub-intensity-dependent signals for calculating and establishing therefrom the relevant disposition of the particle to initiate fire and/or explosion or some other danger.