RISCAuthority insight - September 2018
Dr Jim Glockling assesses whether lessons have been learned about the use of glazed curtain walling in the residential environment
IT MIGHT be said that one of the Grenfell ‘issues’ is that a building method was taken from the commercial environment and applied with little thought to the residential environment, where controls, risks and interest levels in problems relating to fire are very different. Fire is obviously of great interest to the insurance community, because a single event can cause total property loss and such business interruption that the company becomes unviable and never recovers – seldom is this true of other perils, such as security.
Over countless years we have lobbied hard for fire loss in the commercial sector to be recognised more in building regulations, but without life loss we experience little interest. It could be argued that this flippancy leads to one great failing – noone in authority is considering what happens when building methods cross over from commercial (which, let’s not forget, is very heavily regulated for safety and most likely to have other protection systems in place – yet even then has fire issues), to residential, where:
- very different risks exist (ie sleeping risks)
- occupancies can be less fit to cope in fire
- there is little or no control over contents and activities
- investment in protection systems over and above the minimum is scarce
- there is less regulation and system testing than the workplace
In the same way that rainscreen cladding systems have made their way into the residential sector, so too has glazed curtain walling (GCW). Has anyone considered whether this is okay? Clearly GCW is entirely appropriate for the commercial environment, but consideration must be given to whether it is appropriate in its own right (on a standalone material basis), or only in association with the other controls, which may or may not be present in the residential environment.
We can ask this question with some authority. In 1999, when the FPA was the Loss Prevention Council, we conducted – on behalf of UK insurers – one of the largest studies of fire spread in GCW ever undertaken. Our remit was to establish whether the estimated maximum loss (EML) calculations used by insurers had merit.
Competitive insuring seldom assumes that every multi storey building fire will result in a total loss. Instead, assumptions are made on the building’s ability to resist fire spread: a typically crude assumption of a well designed and built building might be that you lose the fire floor to fire, the two floors above to smoke damage and the floor below to water damage – ie insurance is for the loss of four floors, not every floor.
Across 24 full scale tests, we isolated the failure times of each key component: the brackets, the aluminium grid, and the glazing. These times were startlingly short, with glazing failing in 13 minutes and considerably quicker when combustible material was placed on window sills, and even the major components (transoms and mullions) were ‘consumed’ in 24 minutes.
However, the work also demonstrated quite clearly the effectiveness of sprinkler systems in maintaining fire conditions to a level that meant the GCW system was not threatened (and how good fire resisting systems can be). The results were presented to the NFPA in 1999 and the South African FPA in 2008 and at the Tall Buildings Seminar in 2014. A paper can be found at https://bit.ly/2mWcN8t
The overarching conclusions at the time were that, without provision of sprinklers, it was difficult to envisage how uncontrolled vertical fire spread could be avoided. But, at this same time, through the fact that we were talking about a commercial building system, and we had those splendid things called Local Acts in place (now repealed by the former DCLG), GCW probably would have been accompanied by a sprinkler system.
So, what about now? This is not a question on the combustibility of facades. GCW does not burn, but is incredibly structurally weak to fire – from what we understand as a result of our research, its application in the residential environment without a sprinkler system might be foolhardy at best and life threatening at worst. There seems to be no impact analysis made on this – do we have to wait for the problem to manifest again before action is taken?
Dr Jim Glockling is technical director of the FPA and director of RISCAuthority