Smoke Detectors on Common Stairs

[scooby]

I'm not sure which heading this fits under so apologies if it is in the wrong place.

We have a 4 floor block of flats with a "stay put" policy. Each floor is a compartment and has a part 1 detector opening a smoke vent on that floor. The compartment is separated from the stairs by a 60 minute door.

There is a single protected (fire fighting) stair with a manually operated vent above it in the roof.

The Fire Service can use a MCP by the entrance door to open the roof vent if they wish, but there is no smoke detection on the stairwell. ADB Vol1 seems to suggest that if the travel from the fire door to the stairs is under 4.5m, smoke detection is not required on the stairs but am I reading this correctly?

Thanks is advance!

[AnthonyB]

It meets the sprit of 3.9 as there is separation between each landing and the stair which makes a stair OV acceptable - if the stairs were open to the landing they would need an AOV.