for Carbon Monoxide (CO) gas detectors and Nitrogen Dioxide (NO2) gas detectors in underground garages, parking houses and tunnels.

What engined vehicles fumes does the CO gas detectors and NO2 gas detectors detects?

Carbon Monoxide (CO) gas detectors are used to detect Carbon Monoxide (CO) gas from gasoline / petrol engined vehicles.

Nitrogen Dioxide (NO2) gas detectors are used to detect Nitrogen Dioxide (NO2) gas from diesel engined vehicles.

What are the mounting heights for CO gas detectors and NO2 gas detectors?

Carbon Monoxide (CO) gas has a slightly lower density than air.
Recommended mounting height for Carbon Monoxide (CO) gas detector
is 1.5 m above floor.

Nitrogen Dioxide (NO2) gas is heavier than air and sinks in the air.
Recommended mounting height for Nitrogen Dioxide (NO2) gas detector
is 0.2 meter above the floor.

According in garages are concentrations expected less 1%VOL and because of thermal an convection of gas the spreading is at whole area.

How many CO gas detectors and NO2 gas detectors are needed in a stationary installation?

There may exist some consultants, some local regulations or some country regulations, however, there are no absolute rules in determining the number of gas detectors and gas detectors location.
(EN50545 CO&NO2 400m²).
The number of gas detectors are to be decided from case to case depending on the situation of the location you want to detect and monitor.

There are recommendations-guidelines (rule of thumbs).
One gas detector per 400 m2 (i.e. one CO gas detector per 400 m2 and one NO2 gas detector per 400 m2), plus additional gas detectors at the locations where gas leakage is likely to occur, preferably no farther than 1.5 meter where gas leakage is likely to occur.

What are the measuring ppm ranges for pre-alarm and warning alarm for
CO gas detectors and NO2 gas detectors?

CO detectors alarm levels:
Pre-alarm: 25 ppm.
Warning alarm: 35 ppm.

EN50545:
1 = 30 ppm 15 Min. Average Fanspeed1.
2 = 60 ppm 15 Min. Average Fanspeed2.
3 = 150 ppm Current Value = Optical/Acoustic alarm.
Measuring Range:0-300 ppm

NO2 detectors alarm levels:
Pre-alarm: 2 ppm.
Warning alarm: 5 ppm.

EN50545:
1 = 3 ppm Current Value Fanspeed1.
2 = 6 ppm Current Value Fanspeed2.
3 = 15 ppm Current Value = Optical/Acoustic alarm.
Measuring Range:0-30ppm

What is the gas sensor (cell) life time for CO gas detectors and NO2 gas detectors?

CO gas sensor (cell) life expectancy is 5 years, normal operation environment.

NO2 gas sensor (cell) life expectancy is 2 years, normal operation environment.

If gas sensor (cell) is intensively exposed for fumes (gas) the life time is shorter.

If gas sensor (cell) is less exposed for fumes (gas) the life time can be longer.

Are the gas detectors needed to be re-calibrated?

The CO gas detectors and NO2 gas detectors are pre-calibrated before delivery.

The CO gas detectors and NO2 gas detectors are recommended to be re-calibrated on site once a year.

What to do when life time of gas sensor (cell) exceeded the expected life time ?

There are some different alternative choices, for examples:

New gas sensor (cell) can be ordered with re-calibration of the new gas sensor (cell) on existing pcb on site. For this alternative, the re-calibration instructions are needed to be followed very carefully. Recommended to be done of trained technicians.

Existing pcb can be returned to VCP and new sensor (cell) can be ordered.
The existing pcb can be factory pre-calibrated with the new sensor (cell).

New factory pre-calibrated gas sensor (cell) and pcb can be ordered.
Then the installer easily replace the existing gas sensor (cell) and pcb with the new factory pre-calibrated gas sensor (cell) and pcb. This is the easiest way of all above examples.