ClassiFire
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Several Aspiration Smoke Detection (ASD) systems are capable of operating at very high levels of sensitivity. However, only the Stratos family of detectors can continuously maintain an appropriate level of sensitivity in the face of normal fluctuations in environmental smoke density. Such fluctuations may be significant, and they may occur due to a number of factors, such as building occupancy, manufacturing processes and detector air filter clogging.
The unique technology used in the Stratos-HSSD® range is known as 'Relative Sensitivity'. This process is given the name ClassiFire, and is able to establish and maintain optimum alarm thresholds, irrespective of normal background smoke fluctuations. Only AirSense Technology's Stratos products employ this patented and award winning 'perceptive Artificial Intelligence' (AI) technology. All other manufacturers of aspirating systems rely on the inferior 'Fixed Sensitivity Systems' method of determination of alarm thresholds, which is discussed below.
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'Fixed Sensitivity' refers to a smoke detector which produces an alarm output when the ambient smoke level rises above a predetermined and fixed threshold. All detectors apart from Stratos-HSSD and its derivatives use this process. Figure 1 shows how smoke density typically progresses throughout the development of a fire before an alarm signal is generated in fixed sensitivity detectors.
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These systems typically incorporate a moving bargraph display that indicates ambient smoke density against predefined alarm thresholds. The major drawback of fixed sensitivity detectors is that the bargraph scale starts at 0% obscuration per foot (obs/ft) - that is, absolutely clean air. Such a clean, stable atmosphere is typically only found within tightly controlled environments such as semiconductor manufacturing clean rooms. In normal working environments there will always be a certain amount of smoke present from production processes, external activities, vehicle exhausts etc. and this ambient smoke level will tend to vary over time. The performance of fixed sensitivity detectors is significantly affected by these fluctuating background smoke levels, which are displayed on the bargraph and which affect the amount of additional smoke required for an alarm, and hence the detector's sensitivity.
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Figure 2 shows that alarm activation occurs when the combined smoke density of background smoke and fire smoke reaches the alarm threshold. At time 'A', ambient smoke density (S1) is low, so a relatively large amount of smoke (S2) is required from the fire to generate an alarm. At time 'B', S1 (ambient smoke density) is much higher, it now takes only the small additional amount of smoke (S2) to generate an alarm. The detector's bargraph conveys little useful information at either time, since all it is registering is the varying background smoke. At time B, it is possible that a random fluctuation in background could be sufficient to generate a nuisance alarm. The detector has no means of distinguishing between a fire and the normal background, and the actual detector sensitivity to fire at any time depends on the background smoke level.
This means that so-called 'Fixed Sensitivity' detectors actually have a VARIABLE sensitivity to fire! In Figure 2, since S1 and S2 are both variable, detector sensitivity to fire is also variable. |
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Stratos-HSSD continuously adapts its sensitivity to the environment in which it is installed, providing alarm thresholds which are 'relative' to the background smoke levels in the protected area, instead of placing the alarm threshold at a fixed level relative to perfectly clean air. At any time, the detector's sensitivity remains constant, regardless of fluctuations in the normal background smoke level, as can be seen in Figure 3 below. Stratos- HSSD's bargraph display only shows smoke levels significantly above the expected background level, such as from a genuine fire situation.
The philosophy of relative sensitivity is to continuously calibrate the detector relative to the fluctuating background smoke level, so that the thresholds only take into account the increase in smoke caused by a fire. This means that as the background level changes, the threshold must change too. |
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