AFD in cladding voids

[SeaBass]

I've been shown a fire report, for a building with ACM cladding, where the report author has suggested the installation of automatic fire detection in the cladding void, as a means of reducing the risk, to residents, from external fire spread over the building envelope.   

I foresee a number of problems with this approach, including false alarm due to atmospheric contaminants, solar gain and similar. Access for servicing and testing the detectors, the cost, the efficacy of the detectors with so little air space around them and the potential up-draft through the void, to name but a few. 

Has anyone come across a similar arrangement which has worked or been tested? 

[jayjay]

Does not appear to be a suitable solution if the panels are combustible. Assuming that an early warning of fire could be given due to the problems you identified.  If fire is discovered and warning given what happens then ? the fire could be high up or difficult to immediately access. A dry pipe water drencher system would be more effective as a warning would be given in addition to suppression.

[AnthonyB]

If the cladding is that bad I'd want the alarm raised whilst the fire is still in the building before the cladding is involved! I would assume that there is an audible fire alarm system covering both the flats and common areas for these detectors to activate.

We have sites that have been able to retain cladding that fails, but exterior AFD hasn't been the answer, it was only the presence of a full sprinkler system and a cladding mounting system that had suitable firebreaks and no open unstopped cavity that made the case, plus a comprehensive alarm system with C&E that follows stay put (quiet) initially but can be used to evacuate fully or in phases as required. The sites are also on a complex with very good FS Management and plenty of 24/7 staff to respond to incidents.

Many other sites have had to bite the bullet and remove it as the required combined fire safety package wasn't realistically available to retain it.

[Fishy]

I assume as 'residents' are mentioned we're talking high-rise residential (the answer might be different if we're not)?  It has been mentioned within my hearing as a potential solution - but to be honest was never taken very seriously. 

Apart from the technical challenges re: installation, maintenance, day-to-day management, false alarms etc (some of which could be solved) early warning would only really be of much use where immediate simultaneous evacuation is the strategy.  In my view (and this has been said in several Government documents & all the relevant industry guidance) this is not a suitable permanent evacuation solution in high-rise residential properties.

At the end of the day, chucking additional detection at the problem doesn't help much if the building can't be evacuated quickly and reliably and/or the fire strategy relies upon 'stay put'.  The potential is that you just learn you've got a disaster on your hands a few minutes earlier.