Sensors continuously monitor the microclimate for air pressure, temperature, humidity and presence of VOCs and carbon dioxide.
After the sensor runs the calibration process, the BME688 gas sensor within the sensor continuously monitors the microclimate of the forest air to measure air pressure, temperature and humidity. Along with these measurements, It also "smells" the air around the sensor for the presence of Volatile Organic Compounds (VOCs)(1) and carbon monoxide.
- VOCs are compounds that have a high vapor pressure and low water solubility.
Normal Air - Index of Air Quality (IAQ)
By continuously monitoring the microclimate, the gas sensor tracks historic readings of VOCs to produce a stable baseline called Normal Air. This baseline means the air quality does not have VOCs associated with a smoldering fire. This stable baseline is indicated by an Index of Air Quality (IAQ)(1).
- The change in Air Quality (increase in IAQ) can be triggered by several events. Other environmental factors other than fires can cause a deterioration in air quality such as diesel engine fumes in the vicinity of the sensor, moving the sensor or even the breath of someone coming close to the sensor.
Continuous monitoring results in the sensor learning to distinguish between Normal Air Quality and Declining Air Quality:
Normal Air Quality is the result of the 14 day calibration period of the sensor. It is the baseline reading of the air quality.
Declining Air Quality could be the result of fumes from a smoldering fire but it could also be the result of gasses which it has detected such as diesel fumes from a passing truck or other factors that caused a negative change in air quality.
Decline in air quality - increase in IAQ value
Once per minute, the sensor checks the air quality of the microclimate near the sensor. If the air quality has significantly deteriorated within this short period of time (using a default sliding time window of 5 minutes), then this is considered a deviation from normal air quality. This deviation is reflected as an increase in the IAQ (Index of Air Quality).
If the IAQ value has significantly increased from the baseline by a value of 50, then the sensor triggers a Phase 1 detection process. This process is used to determine if the deviation is the result of gasses produced by the smoldering phase of a fire or some other cause.
The sensor may not have detected a fire even though a Phase 1 alert was triggered.
The change in Air Quality (increase in IAQ) can be triggered by several events. Other environmental factors can cause a deterioration in air quality such as diesel engine fumes in the vicinity of the sensor, moving the sensor, or even the breath of someone coming close to the sensor