Pro Dive Central Coast

Oxygen sensors in analysers and rebreathers are sophisticated devices that  operate through a chemical reaction that generates a small electrical current, which is measured to estimate the oxygen pressure present.

Essentially, an oxygen sensor is an electrochemical generator composed of a lead anode, a gold cathode, and a liquid electrolyte, typically a solution of water and potassium hydroxide. Several environmental factors, such as pressure, temperature, humidity, and the presence of oxygen, influence the chemical reaction. Additionally, manufacturing factors, including the purity and precise quantities of chemicals used, significantly impact sensor performance.

The chemical reaction within the sensor begins upon assembly, continues at a slow rate while the sensor remains in its sealed packaging, and accelerates when exposed to the atmosphere. Over time, this reaction consumes the chemicals, leading to degradation of the sensor and a gradual loss of accuracy and reliability.

Various sensor replacement strategies exist, but most rebreather manufacturers recommend replacing sensors periodically before these performance issues arise due to natural aging and usage. The generally accepted maximum useful lifespan of oxygen sensors in rebreathers is 18 months, with typical lifespans of 12 months or less, depending on usage and environmental conditions.

Manufacturers strongly advise against improper storage techniques such as vacuum packing, freezing, or using inert gases, as these practices can cause irreparable damage to the sensors.

• Scheduled Replacement: Install fresh sensors in the rebreather and replace them after 12 months of use. This aligns with the manufacturer’s recommendations, and annual replacement ensures optimal sensor performance.
• Improper Storage: Some divers remove their sensors after each dive and follow a personal storage routine in an attempt to prolong sensor life. This improper handling may lead to sensors that either malfunction or exhibit unpredictable behaviours.
• At the end of 12 months, sensors are discarded, with the diver assuming the risk of sensor failure due to mishandling.
• Ignoring Manufacturer Guidelines: In some cases, divers disregard the recommended sensor replacement intervals, continuing to use sensors beyond their useful life until they fail. 

The rebreather community has established through extensive experience that the effective lifespan of a "10mV in air" oxygen sensor in rebreather applications is between 12 to 18 months.
While most responsible divers adhere to manufacturer recommendations, some continue to question the rationale behind the frequent sensor replacements, suspecting a “hidden agenda” from manufacturers, and opting to extend sensor life on their own terms.