SP has been working in a project focused on assessing the performance of different types of flame detectors. The work was part of a larger project carried out by INERIS (Institut National de l’Environnement industriel et des RISques) which is a large French institute. The objective of the project was to produce advice and recommendations for potential end-users of flame detectors.
SP’s part of the project was to perform outdoor tests of the detectors. These tests were performed in order to evaluate the performance of the detectors in a close-to-reality application. 12 different detectors based on three different technologies were tested using their default sensitivity settings.
IR- and UV-radiation sensor technologies as well as multiple sensors were included in the project.
Two main criteria were used when evaluating the detector response;
• D10, D30: Maximum distance at which detection occurs within a given time (10s=D10, 30s=D30)
• α: Maximum horizontal viewing angle at the D30 distance
These criteria were in turn determined for four different types of fuel; Heptane, Ethanol, Cardboard and Methane. A few tests were also performed using Hydrogen. As part of the evaluation was to determine any effects caused by different weather conditions the weather was closely monitored during the tests.
In order to adjust the distance between the detectors and the fire the detectors were mounted on a portable test rig as shown in figure 1. The horizontal viewing angle was also adjustable for each detector to enable alterations in the line of sight.
The detector response was tested twice, to determine repeatability, for all detectors at up to 22 different distances ranging from 5 m to 80 m away from the fire. Figure 2 displays the longest achieved D30 distance during these two series for each detector and fuel.
It is apparent that the performance can differ substantially between detectors. The influence of fuel can also be seen and it follows roughly the same pattern throughout the whole range of detectors. The large difference in performance seen between the detectors can have several reasons but the most important one found in the tests was the default sensitivity. This conclusion was drawn since there was a wide spread in the performance within both detectors from the same manufacturer and detectors using the same type of technology. This made other derivable differences hard to distinguish in the outdoor tests that were seen in the indoor tests performed by INERIS. Multiple IR-sensor detectors were found to have the overall highest sensitivity in those tests but the differences were small compared to those between different manufacturers and models.
Figure 3 shows the results from the tests of the maximum α-angle. It can be seen that the α-angle is inversely proportional to the D30-distance. As a result the fuels that produced the longest distances for the detectors also got the smallest α-angles. One possible reason is that the sensitivity generally is lower closer to the periphery of the detector. When the fire is closer to the detector it occupies a larger portion of the field of vision which may generate a more consistent alarm signal and compensate for the lower sensitivity when detecting at greater angles. In combination with the effect of overall decreased resolution when moving away from the source this may have caused the relation between D30 and α.
The conclusions from the outdoor tests were:
• The default sensitivity level was the most important parameter
• The type of fuel burning is a substantial factor for detector performance
• Weather conditions such as precipitation and wind speed can affect the performance of the detectors. The amount of data however, was too small to make a certain conclusion about this effect. However, the influence on the results due to weather was small compared to that of for example fuel
• No correlation could be determined between type of detector technology and the detector response time in the outdoor tests. Such a correlation was found in the indoor tests so the reason is most probably the added range of variables in the outdoor tests, such as different weather conditions.
• All detectors except one were fully functional throughout the whole test period despite harsh weather conditions with rain, snow, temperatures ranging between -10°C and +11°C and repeated rebooting.