The Importance of Dewpoint Measurement
in Breathing Gases
Application Note
Breathing gases are essential in a wide range of applications, from medical life support to industrial safety and diving operations. Ensuring the purity and safety of these gases is critical, with trace moisture measurement playing a vital role in maintaining gas quality and protecting users.
What are Breathing Gases?
Breathing gases refer to any gas mixture intended for human inhalation. Breathing gases include medical air, oxygen (O₂), nitrous oxide (N₂O), and mixtures like heliox, delivered via pipelines or cylinders for applications such as:
ambulances and aviation.
support via ventilators.
These gases are supplied via cylinders, pipelines or centralised systems and their composition must meet strict safety and purity standards.
These gases are delivered under strict control, following standards such as ISO 7396 (medical gas pipeline systems), ISO 18562 (biocompatibility of gas paths), European Pharmacopoeia, CGA/ANSI G‑7.1 and OSHA 1910.134.
Moisture Problems in Breathing Gases
Trace moisture, even at very low levels, can cause significant issues in breathing gas supply systems:
Solutions – Dewpoint Measurement
Dewpoint measurement for breathing gases is critical to ensure dryness and prevent microbial growth or corrosion in pipelines.
Here are two common solutions:
- Online Dewpoint Sensors
Continuous measurement using dewpoint transmitters installed directly in the medical air pipeline or sampling line, often used with real-time alarms. Typical measurement range: -40 °C to -70 °C dew point for medical air compliance. - Portable Dewpoint Meters
Handheld or portable dewpoint meters are used for spot check measurements at various sample points and to verify pipeline dryness during commissioning or audits. Key features are fast response, battery-powered and data logging functionality.
Applicable Standards
The 2002 European Pharmacopoeia, published by the European Department for the Quality of Medicines in Strasbourg, describes the method recommended for the determination of the moisture content of medical gases. The recommended maximum allowable moisture concentration is 67 parts per million by volume. (-46 °C dew point).
The Health Technical Memorandum regulates correct use and control of medical gases in the UK. This document has recently been updated to HTM02 and includes the recommendation that “…all medical gas supplies should be continuously monitored for dew point or moisture content”.
EU Pharmacopoeia: Medical oxygen ≤ 67 ppm H₂O (≈ –46 °C dew point).
ISO 7396-1/BS EN 7396-1: governs pipelines for compressed medical gases, requiring safe, moisture-free installation.
UK HTM02: Continuous monitoring, max 67 ppm/–46 °C dew point; typical cylinder content ~5 ppm.
OSHA & CGA G-7.1: Grade D breathing air max dew point –50 °F (~–45 °C).
NFPA 99: Health care facilities
Accurate trace moisture measurement in breathing gases is vital to ensure patient safety by reducing the corrosion and moisture induced damage that leads to equipment malfunctions, infections and compromised therapy, maintaining regulatory compliance under ISO, CGA, HTM and Pharmacopoeia standards. Together, these measures ensure the safe and consistent performance of breathing gas delivery systems.
