While the mounting height of CO sensors is often times mandated under building codes, nitrogen dioxide (NO2) sensors have no standard, regulated mounting height. When deciding where to mount NO2 sensors, it is dependent on the application and the environment involved.
The density of nitrogen dioxide is greater than that of air, indicating that sensors should be mounted near the floor. However, in instances where large vehicles equipped with top-exiting exhaust stacks, hot exhaust gas will rise to the ceiling, and slowly descend as it cools. For this reason, it is recommended NO2 sensors be mounted higher up, in order to detect any potentially dangerous levels of NO2 as quickly as possible.
In applications in which the majority of vehicles include traditional exhaust pipes under the vehicle, we must consider that the hot gas may not reach the ceiling before cooling and descending, and sensors should therefore be mounted at normal breathing level.
In maintenance garages, the height at which employees will be working should also be taken into consideration.
To ensure the safest air quality in a space occupied by diesel vehicles, we recommend that the particular application, the vehicles which will occupy the space, and where personnel will be working should all be taken into consideration before deciding where the NO2 sensors should be mounted.