Survey of the reliability of carbon monoxide alarms deployed in domestic homes and efficacy of use by consumers.

Carbon monoxide (CO) alarms are extensively used in domestic premises in the UK to help protect against CO poisoning. Their expected lifetime has been increasing, and some current models now have a replacement period of more than 6 years under normal operation. However, concerns have been expressed as to the reliability of alarms over an extended period. In this study, 110 households with a CO alarm were surveyed, during which the alarm was uninstalled and replaced and a household survey questionnaire administered. Alarm reliability was assessed under laboratory conditions by testing conformity to the alarm condition gas tests in either the British (European) standard, BS EN 50291 for UK certified models, or the US standard, UL 2034 for US certified models. The questionnaire recorded the alarm make and model, its age, its location, whether it was correctly sited, and how often it was tested. General information on the property was also collected. Results of laboratory testing suggest that the reliability of the most common models of CO alarms used by UK consumers has improved over the last 7 years. However, findings from the household survey suggest that the way alarms are used in many homes may not maximize their ability to detect abnormal levels CO.

Response of electrochemical oxygen sensors to inert gas-air and carbon dioxide-air mixtures: measurements and mathematical modelling.

Electrochemical oxygen gas sensors are widely used for monitoring the state of inertisation of flammable atmospheres and to warn of asphyxiation risks. It is well established but not widely known by users of such oxygen sensors that the response of the sensor is affected by the nature of the diluent gas responsible for the decrease in ambient oxygen concentration. The present work investigates the response of electrochemical sensors, with either acid or alkaline electrolytes, to gas mixtures comprising air with enhanced levels of nitrogen, carbon dioxide, argon or helium. The measurements indicate that both types of sensors over-read the oxygen concentrations when atmospheres contain high levels of helium. Sensors with alkaline electrolytes are also shown to underestimate the severity of the hazard in atmospheres containing high levels of carbon dioxide. This deviation is greater for alkaline electrolyte sensors compared to acid electrolyte sensors. A Computational Fluid Dynamics (CFD) model is developed to predict the response of an alkaline electrolyte, electrochemical gas sensor. Differences between predicted and measured sensor responses are less than 10% in relative terms for nearly all of the gas mixtures tested, and in many cases less than 5%. Extending the model to simulate responses of sensors with acid electrolytes would be straightforward.