Just back from traveling so now I can answer this… Please excuse and delete if this topic is o no value to you…
There are several mechanisms by which Hydrogen (H2) can react and the mere reaction by one mechanism can avalanche into others at a rapid pace. H2 is at the top of the list of what is called Brostead Lowry acidic proton donors… so if there any trace of moisture nearby, H2 + 2H2O forms 2H3O+, called Hydronium, which is an extremely reactive acid. It’s formation is catalyzed (meaning the activation energy for formation of the specie is drastically lowered by) metals; noble metals give the lowest activation energy…(this is all equationally captured by Arrhenius rate chemistry that I will not go into here)… but aluminum and steel are still fine catalysts that can lower the temperature of formation from about 500C as required to happen spontaneously, to about 3C with a suitable catalyst. Once formed the Hydronium will attack anything neutral or negatively charged with enormous energy release… including oxygen in the air… which is electron rich. (nb. Refineries use metals like platinum, nickel, and rhodium on supports like diatoms as a catalysts in their unit ops, but control the reaction rate with temperature, pressure, and reacting reagent concentration). Pure hydrogen burning in air emit ONLY ultraviolet waves (non-visible to the human eye), and thus ultraviolet glasses or some sort of ultra violet detectors are used to tell if there is danger in commercial plants. You could literally walk into an area with leaking H2 and only feel heat, and because H2 is generally under pressure, it can act like an invisible blow-torch that an unsuspecting victim may find too late.
So how does this self-ignite with hydrocarbons? A hydronium ion is constantly seeking sources of electrons to neutralize. Carbon rich hydrocarbon chains like grease will make an ideal source of fuel for such molecules which react could violently, but most often is controlled by diffusion of Hydronium in air. In this case, flames from the burning hydrocarbons are blue (smaller molecules like butane) to yellow in color (pentane and to decane) or even black (C10+). The reaction needs no catalyst because the activation energy is negative signed at ambient temperatures and pressures. H3O+ and HxCy… form H2O plus a number of fractional hydrocarbons from the burning process.
An additional note (from other sources); H2 can dissolve in many metals, leak out, and have adverse effects on them, like hydrogen embrittlement that leads to cracks and explosions. Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns
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