I've come across this before. Here are some issues:
1. The buildings these system are proposed for are defend in place - but if people become aware of a fire next door, which they are very likely to do if it is a sizeable fire, they are much more likely to try to get out than to shut the door to their flat and carry on watching Coronation Street.
2. With the ADB compliant layout the flats in the dead end are exposed to risk from one other flat, the flats in the two way part of the corridor are exposed to risk from 5 other flats - but, importantly, they have the option to turn away from the fire and smoke source.
3. With the Colt system each flat is exposed to risk from a much greater number of flats - 10 in their illustrative diagram. Few of the occupants may have the option to turn away from the source of the smoke. If the fire flat is near the inlet, occupants near the outlet have all the products of combustion directed to them.
4. Items 2 and 3 above are part of the point of limiting travel distance - they are more significant than the number of metres you have to walk to get to the storey exit.
5. Regarding the CFD videos Colt present, they seem to be simulating two puffs of smoke into the corridor; one, presumably, when the occupants leave and one when the fire service arrive.
6. They have assumed zero wind for their CFD modelling which is extremely unlikely and very unfair on the AOV scenario. This undermines the AOV video and so this should be treated as false.
7. There are many other possible scenarios apart from the two individual puffs of smoke into the corridor (albeit that they are large puffs) that should be considered. What if there is continual seepage of smoke from a flat door, what if the flat door fails to close properly, what if the flat doors fails (it's only half hour fr). CFD should be performed for all likely scenarios. Without this being done, little confidence should be had in the system.
8. Other systems sometimes provide input fans with natural ventilation. This has a different effect to the provision of output fans with natural inlets as proposed here. Colt mention very briefly the depressurisation of the corridor caused by their system. This should be quantified in any specific application. It could have an effect on the movement of fire products from the fire flat into the corridor and on the effort required to open a flat door away from the depressurised space. That said, a system that results in a positive pressure in the corridor could move fire products from the corridor into the adjoining flats. At the end of the day, any manipulation of pressure differentials should be quantified and analysed for effects.
9. The temperature of the smoke from a flat door adjacent to the fans should be assessed to make sure that the fans are appropriately rated.
10. The whole lifetime of the building must be considered and the likely lifetime of the system (bearing in mind testing and maintainance regimes) should be compared with this to ensure that the building will remain safe for its whole lifetime. If the building is likely to still be there in 100 years time, it should be asked of Colt, is your system likely to last 100 years?
All in all, acceptance of the system should only be based on rigorous analysis of it's performance under a variety of scenarios.
I know that AOVs aren't brilliant and that Colt only have to show that their system is at least as good as AOVs, but do ask them to do that properly and don't let them rely on the generalisations given in their sales pitch.
Having said all that, in this case, because it's only 9 m, I'd go along with BCO's comments above.
11.
