Experimental study on responsiveness of multi-spectrum infrared flame detectors to diffuse flames partially hidden by obstacles installed in oil and gas processing facilities

Multi-spectrum infrared flame detectors are commonly installed in many oil and gas processing facilities for an early fire detection. Since these facilities are filled with equipment and piping, the visibility of flames from infrared flame detector is a critical factor for reliable and early detection. However, conventional methodology of fire mapping study does not consider the three-dimensional spread of flames. Therefore, this paper focuses on the responsiveness of multi-spectrum infrared flame detectors under the condition that flame is partially hidden by such obstructions. A series of full-scale experiments was conducted to examine the responsiveness of infrared flame detectors to flames partially hidden by shielding objects. These experiments simulated various conditions seen in the oil and gas processing facilities. The experiments have confirmed the relationship between the intensity of infrared energy and the obstruction ratio. Specifically, the infrared energy at a wavelength of 4.504 μm emitted from a flame hidden by shielding objects can be quantified using the obstruction ratio, the ratio of visible area of partially hidden flame. By using these indices, it has been clarified that the infrared energy emitted from a partially hidden flame at the location of an infrared flame detector can be estimated. The responsiveness of detectors depends more on the intensity of the infrared energy near 4.5 μm than on flame pulsation. Multi-spectrum flame detectors, commercially available and employed in this study, exhibited performance equal to or even more sensitive than what is stated in their data sheets. Quantitative evaluation of the responsiveness of flame detectors to partially hidden flames revealed in this study can contribute to the improvement of the fire mapping study for the realistic design evaluation in the oil and gas processing facilities. •A series of full-scale experiments was conducted to examine the responsiveness to the flame partially hidden by obstacles.•New index, Obstruction Ratio, is proposed for the evaluation of the effect of the shielding objects.•The responsiveness of detector is much depended on the intensity of the infrared energy rather than the flame pulsation.•The responsiveness of multi-spectrum infrared flame detectors can be judged from commercially available data sheet.