Victoria University fire safety expert Dr Geoff Thomas asks how relevant the lessons of the Grenfell Tower fire are for New Zealand
In the wake of the Grenfell Tower fire in London, which killed at least 79 people and probably more, much comment has been made in New Zealand about the advantages and shortcomings of our own system of fire compliance in buildings. It is important to draw lessons from this tragedy, but we should do so in a considered way, and some of the suggested lessons for this country are of questionable relevance.
At this stage, the main contributors to the high number of deaths in Grenfell Tower appear to have been the rapid external fire spread via aluminium and polypropylene sandwich panels, the slow evacuation time due to the height of the building and the provision of a single exit stair, but primarily the strategy of “defend in place”, with occupants previously instructed to stay in their apartments until told to evacuate by the fire service.
This strategy can only be used in New Zealand in a building with automatic sprinklers and smoke detection, and staff who have been drilled in evacuation procedures. Occupants are evacuated to areas with barriers (for example, floors, roofs and walls) between them and the fire location that have had prototypes tested and rated for their ability to withstand fire in the highly unlikely event the sprinklers fail to control it. Such buildings include hospitals, rest homes, prisons and a few very tall buildings.
Without automatic sprinklers, as was the case in Grenfell Tower, the strategy depends on the reliability of fire ratings. The authorities responsible for its use in Grenfell Tower appeared to believe the one-hour fire rating between apartments would give one hour of protection. But the rating is based on a standardised test that is typically conducted in a much less severe thermal environment than a fully developed building fire. For a standard domestic room, the one-hour tested rating can be equivalent to 20 minutes or less in a fire like Grenfell Tower’s.
A further factor, in New Zealand as in the United Kingdom, is that fire separations are frequently not properly installed or maintained, with such failures implicated in the Lakanal House fire in London in 2009, where six people died. Vertical shafts for building services, lifts, stairs and floors will have wiring, piping and ventilation ductwork running through them. These penetrations must be sealed with fire-resistant fittings or material to prevent fire spreading. But it would be rare for any building to have all these installed during construction and they are frequently removed and not reinstated when repair or maintenance work is carried out.
If walls to stairs, or between apartments, are not properly fire rated, the safe evacuation of the building before escape routes are compromised by the effects of smoke and fire cannot be expected. Similarly, fire and smoke doors protecting escape routes are often compromised by self-closers on doors being disabled or doors being wedged open.
Another example of a rating that may vary from real-life use is the AS/NZS3837 test for the cores of sandwich panels for external walls. In this test, the sample is orientated horizontally, whereas in a wall panel it is obviously orientated vertically. Ignition is tested using an electric spark, whereas on the exterior of the building flames may impinge directly upon a panel, as well as it being subject to radiant heat.
In service, the panel systems rely to some extent upon their encapsulation by aluminium to limit flames spreading. However, this requires a high degree of attention to be paid to the detailing of joints and junctions with windows and other openings, which may not be achieved on site.
Testing in Italy on external insulation with flexible coatings showed a two-fold difference in the maximum rate of heat energy emitted between samples assembled by different installers, and if a sample was damaged with a 20mm x 15mm hole in the coating the maximum rate of heat energy emitted was more than 25 times higher.
In any case, tests are only comparative. All materials react to the extreme temperatures in fire in one way or another, and the so-called “fire-resistant” and “non-combustible” panels will ignite and spread fire when subjected to sufficient external heat, but will do so more slowly than the untreated product.
If such panels had been installed on Grenfell Tower, the number of people who died is likely to have been substantially fewer, but there is no guarantee it would have prevented all deaths.
New Zealand has had restrictions on cladding for buildings greater than 25m in height with sprinklers and 10m without sprinklers since 1992, and the type of panels used in Grenfell House’s retrofit were not commonly used before then.
A building of Grenfell House’s size and type built in New Zealand since 1963 would be required to have more than one exit stair and an automatic sprinkler system. Although in Grenfell Tower the fire appeared to spread up the outside of the building, it seems to have started inside, and with an automatic sprinkler system controlling or extinguishing the fire it would have been unlikely to spread to the façade. Since 1992, such a building in New Zealand would also have to have an automatic smoke-detection system.
A much greater risk in this country are smaller multi-unit residential dwellings where building-wide automatic alarm systems are not required and the fire separations are inadequate, particularly in older buildings and converted houses.
Buildings are also at high risk when being altered, as fires are more likely to start during construction work, sprinklers and alarm systems are deactivated in the work area, some egress routes may not be available, fire-rated walls and floors may not be intact, and contractors frequently wedge doors open and disable self-closers.
With automatic sprinklers and without a “defend in place” evacuation strategy, a similar disaster to Grenfell Tower is unlikely to occur in New Zealand. It is more important to address the issues we do face in ensuring buildings are built and maintained to comply with building codes and older buildings are upgraded so they stay safe from fire.