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Last Word is Â鶹´«Ã½â€™s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com

There may be millions of tonnes of white hydrogen available for power. Since each reaction needs oxygen, could it deplete our air supply?

Mike Follows
Sutton Coldfield, West Midlands, UK

In 1987, a well in the Malian village of Bourakébougou unexpectedly ignited when a worker lit a cigarette nearby. The incident drew the attention of a local entrepreneur,…