Investigation into the Cross-sensitivity of Domestic Carbon Monoxide Alarms to Hydrogen

Preliminary research suggests domestic carbon monoxide detectors with an electrochemical sensor are approximately 10 -20% sensitive to hydrogen atmospheres in their factory configuration. That is, the display on a carbon monoxide detector would give a carbon monoxide reading of approximately 10-20% of the concentration of hydrogen it is exposed to. Current British standards require detectors to sound an alarm within three minutes when subjected to a continuous concentration of ≥ 300 ppm CO. This would equate to a concentration of 1500-3000 ppm hydrogen in air, or approximately 3.75 – 7% %LEL. The current evacuation criteria for a natural gas leak in a domestic property is 20 %LEL, indicating that standard carbon monoxide detectors could be used as cheap and reliable early warning systems for hydrogen leaks. Given the wide use of carbon monoxide detectors and the affordability of the devices, the use of carbon monoxide detectors for hydrogen detection is of particular interest as the UK drives towards energy decarbonisation. Experiments to determine the exact sensitivity of a range of the most common domestic carbon monoxide detectors have been completed by DNV Spadeadam Research & Testing. Determining the effects of repeated exposure to varying concentrations of hydrogen in air on the sensitivity of electrochemical sensors allows recommendations to be made on their adoption as hydrogen detectors. Changing the catalysts used within the electrochemical cell would improve the sensitivity to hydrogen, however simply calibrating the sensor to report a concentration of hydrogen rather than carbon monoxide would represent no additional costs to manufacturers. Having determined the suitability of such sensors at an early stage; the technology can then be linked with other technological developments required for the change to hydrogen for domestic heating (e.g. change in metering equipment and appliances). This report finds that from five simple, and widely available carbon monoxide detectors, the lowest sensitivity to hydrogen measured at the concentration required to sound an alarm within three minutes was approximately 10%. It was also discovered that as the hydrogen concentration was increased over the range tested, the sensitivity to hydrogen also increased. It is proposed that coupling these devices with other elements of the domestic gas system would allow actions such as remote meter isolation or automatic warning signals sent to response services would provide a reliable and inherently safe system for protecting occupants as gas networks transition to net-zero greenhouse gas emissions. In this respect, it is noted that wireless linking of smoke and heat detectors for domestic application is already widely available in low-cost devices. This could be extended to CO detectors adapted for hydrogen use.