Measurement equipment

  • Breathing machine: Respironics CA-3200
  • CO2 sensors: GSS SprintIR-WF-20
  • CO2 flow meter ABB PurgeMaster FP-1/4-41-G-3/37
  • Pressure sensor: Sensirion SDP816-500PA
  • Data aquisition: Arduino Mega
Test setup for measuring CO2 concentration in inhalation through half face mask.

Validation targets

  • CO2 measurement
  • Cycles and volume flow

Validation strategy

Carbon dioxide concentration

  • Volume flow over sensors: Pressure differential over CO2 sensing loops are measured as well as the flow through the sensing loop.
  • Adding dead volume: Dead volume is added to the system in the form of 32mm PVC piping.

Pressure drop over mask

  • Volume flow: Outlet is blocked by mask

Validation test data

Volume flow over sensors

SensorPressure drop inhalePressure drop exhaleFlow inhaleFlow exhale
Exhale sensor~0 Pa1000 Pa~0 L/min5.8 L/min
Inhale sensor2750 Pa~0 Pa11.5 L/min~0 L/min
Pressure drop and flow over inhale and exhale CO2 sensors.

Known dead volumes

CO2 test results of different dead volumes added to test setup.
Dead volumeCO2 ExhaleCO2 InhaleTheoretical
0.045.06%0.12%0.10%
0.205.10%0.48%0.51%
0.335.20%0.86%0.87%
Measured CO2 concentration using different dead volumes with an average inhale volume of 1.97L

Volume flow under pressure drop over mask

CO2 test of Dräger Piccola VRAD-F028

Tested masks

Masker nrNameInhale CO2 concentration [%]Exhale CO2 concentration [%]Inhale volume [L]
163M 83200.915.242.07
25BIZTEX NIOSH N950.665.222.10
27VWR 113-06450.875.402.07
20Dräger Piccola VRAD-F0280.935.392.09
263M Aura 1883+0.905.322.05
30Starchem PADM-10V0.585.252.06
19UQ 509/680.735.242.05
Test results of different half face masks, each certified according to the NEN 149 norm.

Conclusion

  1. Pressure drop and flow over sensors show that the corresponding sensors are only experiencing a volume flow under inhalation and exhalation
  2. The large pressure drop over the sensors ensures a large volume flow and a short response time.
  3. Dead volume test shows direct correlation between the added dead volume and the measured CO2 concentration in the inhaled air
  4. The CO2 concentration in the inhaled air corresponds with the theorized increase by adding dead volume
  5. Inhale volume and exhale CO2 concentration is within +- 5% of the desired value of 2L and 5%.
  6. Inhale CO2 concentration without mask is higher than the ambient CO2 concentration (0.04%), this can be explained by rebreathing of the exhaled air around the dummy head. (This was also verified by elongation of the inhalation CO2 measuring tube beyond the head)
  7. The inhale CO2 concentration is for all masks below 1% as is expected from masks certified according to NEN 149 norm.

Downloads

https://1drv.ms/u/s!AqC74CqqYVbpgeAWwgrmCQX7ErizZw?e=YXJFsX