How does pressure affect the ignition of a hydrogen and oxygen mixture?

The relationship between pressure and the ignition of a hydrogen and oxygen mixture is defined by specific explosion limits. While a single temperature typically corresponds to a given pressure, a single temperature may correspond to one or three distinct pressures at which the mixture can ignite.1

The mechanism of the reaction dictates these limits: combustion can only be initiated when the steps in the reaction sequence occur faster than the terminal steps, such as the recombination of atoms or the adsorption of active particles on surfaces. Because the reaction mechanism is complex and involves rapidly varying temperatures and concentrations, empirical expressions are used to predict these phenomena rather than a single universal equation. Consequently, for ignition to occur via an external source like a spark, the energy provided must exceed certain minimal values determined by these specific conditions.21