Across the aviation industry, fire protection remains critical to aircraft design, testing and certification. This applies to OEMs such as Boeing and Airbus, as well as tiered system suppliers. One of the most significant fire-related risks is the potential for fuel tank explosions, which can be triggered by factors such as electrical malfunctions, lightning strikes, or static discharge.
Aircraft manufacturers use several strategies to reduce this risk. One of the most effective is lowering the oxygen concentration inside the fuel tank. This is typically achieved through fuel tank inerting, introducing inert gases like nitrogen to displace oxygen and prevent combustion.
Among the essential components of an effective inerting strategy are oxygen sensors that can continuously monitor oxygen levels and provide feedback to the OBIGGS control system. Zirconium dioxide (zirconia) oxygen sensors have become the industry standard in this domain due to their accuracy, reliability, and resilience in the harsh conditions typical of aviation environments.
This article explains how zirconia oxygen sensors support aviation fire protection and OBIGGS. It is intended for engineers involved in aircraft safety, fuel tank design and sensor integration.
Reducing Fuel Tank Explosion Risk in Aircraft
Fuel tank explosions represent a serious safety hazard and have been the subject of comprehensive research and development efforts within the aerospace sector. One of the foundational principles of fire prevention in aircraft fuel systems is removing one of the fire triangle’s critical components—oxygen.
To achieve this, most modern aircraft utilize On-Board Inert Gas Generation Systems (OBIGGS). These systems use Air Separation Modules (ASMs) to extract nitrogen from compressed air, generating Nitrogen-Enriched Air (NEA) that is pumped into fuel tanks. The NEA reduces oxygen levels to below the flammability threshold, rendering fuel vapors inert and greatly minimizing the risk of ignition.
While commercial aircraft typically rely on OBIGGS, military aircraft employ a broader range of inerting technologies, including reticulated foams, halon systems, and liquid nitrogen. These approaches are tailored for the more extreme operating conditions and combat-related risks faced by military platforms.
Regardless of the method, the performance of inerting systems is highly dependent on precise monitoring of oxygen levels. Inaccuracies in measurement can compromise safety margins, leading to an increased risk of fire or explosion. This is where zirconia-based oxygen sensors play a vital role.
The Engineering Advantage of Zirconia Oxygen Sensors
Zirconium dioxide oxygen sensors, also known as solid electrolyte oxygen sensors, are uniquely suited for aerospace fire protection applications. These sensors offer real-time, high-resolution measurements of oxygen concentration, which is critical for maintaining the effectiveness of fuel tank inerting systems.
Continuous Monitoring of Inerting Performance
In OBIGGS and similar systems, zirconia sensors allow for continuous feedback on oxygen levels within the fuel tank environment. This data can be used to regulate the flow of nitrogen and ensure that the system maintains the required oxygen threshold for fire suppression. By doing so, the sensor enables dynamic control and adaptive safety responses during flight.
Redundancy and Layered Safety Strategy
Fire prevention in aviation benefits from a layered safety architecture. While OBIGGS and inerting methods passively reduce oxygen concentration, zirconia sensors serve as active diagnostic tools. This dual approach provides redundancy. If inert gas delivery is compromised, the sensors detect rising oxygen levels and trigger an alert before hazardous conditions develop.
Detecting System Degradation or Leaks
Zirconia oxygen sensors are also instrumental in diagnosing potential faults within the inerting system. For example, an unexplained increase in oxygen concentration could indicate a leak or malfunction in the ASM or distribution lines. Early detection enables timely corrective action, reducing the risk of safety-critical system failures and minimizing downtime.
SST’s Zirconia Oxygen Sensors for Aerospace Applications
SST develops a portfolio of zirconium dioxide oxygen sensors specifically engineered for aerospace environments. These sensors are used by leading aircraft manufacturers, including Boeing and Airbus, and are integral to many of their OBIGGS installations.
These sensors are designed for durability under harsh conditions—high vibration, temperature extremes, and continuous operation. They employ ceramic-based sensing technology, which offers:
- Fast response time
- High measurement accuracy
- Excellent long-term stability
- Resistance to contamination and degradation
Each sensor measures the oxygen partial pressure difference between a reference air source and the sample gas from the fuel tank. This measurement is then fed into the OBIGGS controller, which adjusts nitrogen generation and distribution accordingly.
In addition to their robust sensing performance, SST oxygen sensors integrate with a range of system architectures and fuel tank geometries. Streamlined installation and maintenance can help aircraft operators reduce service costs and maximise system uptime.
Frequently Asked Questions
What role do oxygen sensors play in aircraft fuel tank inerting systems?
Oxygen sensors continuously measure oxygen concentration within the fuel tank environment. This measurement provides feedback to the On-Board Inert Gas Generation System (OBIGGS), helping it maintain the nitrogen-enriched atmosphere required to reduce fuel vapour flammability and ignition risk.
Why are zirconia oxygen sensors suitable for OBIGGS applications?
Zirconia oxygen sensors provide fast, accurate, and continuous oxygen measurements. Their durability, long-term stability, and ability to operate under demanding conditions make them suitable for aircraft systems exposed to vibration, temperature changes, and continuous operation.
Can zirconia oxygen sensors help detect OBIGGS faults or leaks?
Yes. An unexpected increase in measured oxygen concentration may indicate an air leak, a distribution-line problem, or degradation within an Air Separation Module. Early detection allows the aircraft control or maintenance system to flag a potential fault before safety margins are compromised.
How can SST support an aircraft oxygen-monitoring application?
SST provides zirconia oxygen sensors in different configurations for integration into OEM oxygen-monitoring systems. SST’s engineering team can help assess the measurement requirements, operating conditions, and integration needs of a specific aircraft fuel tank inerting application.
Conclusion
Fire protection in aviation is a complex and multifaceted challenge. Effective fuel tank inerting is a proven way to reduce explosion risk. Accurate zirconia oxygen sensors are essential to its operation.
By providing accurate, reliable, and continuous measurement of oxygen levels, SST’s zirconium dioxide oxygen sensors play a critical role in modern aircraft safety systems. These sensors enable OBIGGS and other inerting methods to function optimally, ensuring that both commercial and military aircraft maintain the highest safety standards.
If you are developing, upgrading or maintaining an aerospace fire protection system, our engineering team can help. Contact us to discuss your oxygen-sensing requirements and how SST technology could support your platform.
