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A unique humanitarian, scientific, and technical experiment is currently taking place in a forgotten mountainous region of West Africa. The experiment is on the verge of reaching its operational stage, which consists of the eradication of a “new” natural hazard; one that is potentially devastating, but which has been known for only 20 years. The Lake Nyos catastrophe, which claimed 1800 victims in August 1986, was not unprecedented. Indeed, 2 years previously a lethal gas burst, originating from nearby Lake Monoun in the same remote area of Cameroon, killed 37 people—an odd and tragic episode that went almost unnoticed. One had never before heard of Mother Nature asphyxiating human beings and most higher animals on such a scale in a single and brief non‐volcanic event.

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The sensing behavior of a potentiometric hydrogen sensor based on polybenzimidazole doped with phosphoric acid as the electrolyte and an E-TEK gas diffusion electrode as the sensitive electrode at room temperature is reported. The open-circuit potential (OCP) in N 2 -H 2 mixtures obeys the Nernst equation with an accuracy equal to 0.1% of the hydrogen partial pressure. The 90% response time is equal to 10 s. In the presence of water vapor, an additional junction potential must be taken into account to describe the potentiometric behavior. The OCP in air containing hydrogen shows a sharp transition located at a H 2 /O 2 ratio equal to 0.61. For hydrogen partial pressures lower than 8 ϫ 10 3 Pa, it varies linearly with the logarithm of the hydrogen partial pressure with a slope almost equal to 130-140 mV/dec which exceeds the Nernst's value. The shape of the potentiometric response under opencircuit conditions is explained on the basis of the mixed potential model. The 90% response time in air is equal to a few minutes. The presence of water vapor slightly influences the potentiometric response.