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Humidity and quality measurement when generating compressed breathing air

Breathing air in the compressed form, such as that used by divers, but also by firefighters in action, has to meet limit values for chemical components such as oxygen, nitrogen, carbon monoxide or carbon dioxide as well as requirements for water and oil content.

The exact limit values are described in DIN EN 12021: 2014-07 and briefly clarified in the table below.

Breathing air Norm DIN EN 12021: 2014-07


Oxygen content (O2)

21 % ± 1 %

Carbon monixide content (CO)

5 ppm

Carbon dioxide content (CO2)

500 ppm

Oil content

0,5 mg/m3

Water content (H2O)

25 mg/m3

If these limit values are not adhered to, considerable damage to life and physical condition can result. For example, too high a moisture content in the press / compressed air bottles can lead to the following:

Corrosion in the breathing air cylinders

The breathing air cylinder can be damaged by creeping rust without noticing it. Unintentional accidents can occur due to malfunctions when using damaged bottles.
Inhaling corrosive components is also harmful to health, so creeping personal injury can occur even without a malfunction.

Breeding ground for mold or other harmful bacteria

Too much moisture promotes the growth of mold or bacteria. Inhaling these can lead to pneumonia and other serious diseases.

Ice formation at low temperatures

During extreme diving in waters with temperatures close to freezing point, ice formation in breathing air cylinders can lead to dangerous situations. If the bottle outlet freezes underwater, it can lead to death in the worst case.

Too high oil content in pressurized / compressed air cylinders

Oil aerosols and particles: In addition to permanent breathing difficulties, inhaling oil mist can, in the worst case, lead to cancer. Aerosols also usually contain the smallest metal particles, which do not favor the situation.

For the proper monitoring of your breathing air in compressed air cylinders, we recommend:

FA 510/515 - Dew point sensor for refrigeration dryers

Dew point measurement from -20 to 50°Ctd. New: with Modbus-RTU interface.


FA 500 - Dew point sensor with integrated display and alarm relay

Ideal instrument for dew point measuring for all kinds of dryers.


Particle counter PC 400 - mobile solution according to ISO 8573

PC 400 particle counter up to 0.1 µm for compressed air and gases in a service case.


Residual oil content measurement OILCHECK according to ISO 8573 - mobile solution

The residual oil content sensor OILCHECK measures the vaporous residual oil content in the compressed air. For a mobile solution we offer you a combination with the particle counter PC 400 and mobile chart recorder DS 500 mobile.