Hi Messy,
It's right that this scenario is inadequately addressed in the standard guides. I think that it is because very few buildings have significant means of escape going up stairs; usually, at most, people might ascend one level.
I think you're absolutely right to seek more appropriate guidance and I appreciate that this is hard to come by. Guidance figures for staircase capacities are based on a combination of flow rates and holding capacity so the significance of a slower flow rate is reduced but it is not negligible.
PD 7974-6 gives some information that could assist:
"Fruin presented a range of values for travel speed on stairs, according to age and sex. For travel downwards, these ranged from 1.01 m/s for males under 30 years, to 0.595 m/s for females aged over 50. For travel upwards, they ranged from 0.67 m/s for males under 30, to 0.485 m/s for females over 50. Fruin?s figures are calculated from observations made on two staircases, one with 7 inch risers and 11.25 inch treads, and one with 6 inch risers and 12 inch treads. Travel speeds up and down were faster for the stairs with the smaller rise height.
"Nelson and Mowrer present travel speeds for four different stair designs (of rise height between Metrificate 6.5 and 7.5 inches, and tread between 10 and 13 inches). They give travel speeds ranging from 0.85 m/s to 1.05 m/s, with speed increasing as rise height decreases. There was no differentiation between upwards and downwards travel, nor were the data broken down by sex and age."
God knows what "Metrificate" means. I think it's an editor's note telling the drafter to convert the measurements to metric. Anyway....
The Nelson and Mower stuff is not very useful but Fruin has downward speeds of 0.595m/s to 1.01m/s and upward speeds of 0.485m/s to 0.67m/s. That's a reduction in speed of around 20% to 33%. As stated, the capacity is based on holding capacities as well as flow rate. Without undertaking tests involving hundreds of people we have no firm method of converting these speed reductions to adjusted capacity figures.
However, applying the 33% reduction to the capacities given in ADB or BS 9999 would certainly err on the side of safety. This might be too onerous and it might be reasonable to halve this reduction to 16% as flow rate is only one half of the two governing factors.
As for Lyle's two gentlement puffing and panting up the stairs, I would say that there should be a well thought through, implemented and practised protocol for assisting people with reduced mobility.
