Wikipedia's use of the word "highly" is more embellishment than fact. If you read the technical papers it is described as "flammable". In the context of our conversations here, where we are dealing with gasoline and diesel fuel, the concerns of hydrogen as a dangerous "combustible" take a back seat. Only under pressure and with proper Oxygen availability is it a highly combustible. Remembering burning hydrogen gas in HS chemistry?
If it were truly "highly" combustible, as gas from a Bunson burner, for instance, the experiment would be outlawed.
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