Why pump access and low bulkheads failed

By the time flooding reached Boiler Room No. 5, was it already too late to open the doors and run pump hoses?

Yes; the access problem was real, and full-height bulkheads with safer upper passages would have bought more time for pumping and damage control.

By the time water reached Boiler Room No. 5, opening the necessary doors to run pump hoses was already impractical. A compartment boundary should therefore continue high through the hull, with cross-ship access kept above the threatened flooding level. If a lower compartment is sealed, compressed air can oppose incoming water and slow the rate of ingress for a time. That pressure balance is temporary because air eventually escapes, but it may create a margin in which pumps and damage-control teams can work. Pump capacity is useful only when the ship's layout preserves access and contains the water those pumps must handle.