If an enclosure has internally, a source and cause for an catastrophic explosive failure, the energy from such will escape from any weakest point. Absent a sufficiently weak point planned into the construction (like a blow off valve in Compressor tank) catastrophic equipment enclosure failure can occur at any point of the enclosure. A normal enclosure is designed only to prevent incidental contact with live parts and to support the internal components not to contain an explosive event. But that being, also the weakest point would be the enclosure's natural openings primary of which would be the equipment door. That is why they make explosion proof enclosure if a sufficient concern of such an event was to be expected and warranted.
This inquiry seems to be related to another inquiry you made similar to the equipment you currently are asking about. If door of enclosure is not aimed toward the egress path you had referenced, and in that the weak point of the enclosure (usuall the equipment door or opening) it would dissipate the majority of the explosive energy away from staircase. A fireball related to an explosive event may however make the person on the staircase within an area susceptible to potential injury from a fireball. But that could be said of any equipment and any egress design and the personnel in the environment from that perspective. Thus approach boundaries in OSHA and NFPA-70E.
