As of this writing, London's Grenfell Tower fire death toll now stands at 30, with 70 more either unaccounted for or not expected to survive. The total death toll may exceed 100.
Information is still coming in regarding the fire, but at least one thing is certain at this point: The facade of the building was retrofit last year with insulating panels that were not designed to resist fire. The system is a composite metal and plastic system called Reynobond
Systems such as this sandwich a thermoplastic material between thin metal sheets. It might seem like this is a fireproof way to build – after all, metal doesn't burn, right? The problem is, the plastic between the sheets does – very easily. It is hydrocarbon (petroleum) based - think of plastics as solidified gasoline in terms of energy density. Once ignited, they are nearly impossible to extinguish – unless it is manufactured with a fire retardant embedded inside of it. If the metal cladding on these sheets gets hot enough, the plastic inside melts and burns. Aluminum melts at 1,221 degrees Fahrenheit. Unfortunately, thermoplastic materials ignite at between 400 and 600 degrees, and burn as hot as 1,700 degrees – well above the melting point of aluminum. There are versions of Reynobond that are fire resistant. Unfortunately, they were not used at Grenfell:
The fire appears to have started on a lower floor. It quickly spread outside to the building facade. Burning plastic gives off extremely toxic smoke which can incapacitate and kill a person in a matter of seconds. Fire rises vertically and spreads horizontally. Once the panels on the lower level started burning, the fire quickly spread, engulfing the entire building, hopscotching its way from floor to floor, and igniting the interior spaces as it went. People rarely burn to death. It's the smoke that kills. The people who were injured or who died were most probably incapacitated by it before they could exit the structure.
American Building codes are very explicit about the testing and use of systems like Reynobond:
Yes, reading these sorts of documents is a snooze. Interpreting them is even more difficult. Owners and architects often find their requirements limiting and costly. Ignoring or trying to circumvent them however is a big mistake - sometimes deadly consequences. Note that building codes are minimum requirements. Good architects work to exceed them. Responsible owners respect this and try to make their buildings safer than codes dictate.
As a sidelight, exterior insulating and finishing (EFIS) systems similar to Reynobond have a long and troubled history in the building industry. Marketed as a cheap and environmentally beneficial building product due to their relatively high insulating values, they have spread throughout the world in newer construction. Prior to the year 2000, these systems were generally designed as sealed enclosures much like traditional systems. The problem with this is that once moisture entered or condensed inside of these systems, mold and rot often spread to other building components, and even to the building interior, causing cosmetic, structural and even health problems. This triggered many construction lawsuits.
The solution to this problem was to create “ventilated facade” systems (rain-screens) that resisted moisture infiltration, but didn't necessarily prevent it. The small amounts that did penetrate were allowed to drain and were dried by air circulation. However, the same construction detailing that allows moisture to escape also must allow air to circulate behind the facade – and of course fire loves air.
I have not seen the construction details of the Grenwell Tower facade retrofit, but it is highly likely that the rain-screen principal was used here. London has a wet, cold climate. If designed as a rain-screen, once fire got behind the panels it would be impossible to extinguish with fire hoses. Remember: such systems are designed to resist the penetration of water.
This in an example of the sort difficult trade-offs architects must make when designing even simple structures. Codes serve as a guide, but its important to look at the big picture – the intent of the code – when designing buildings. Architects are trained to do exactly that. This is why architects are in charge of coordinating and overseeing all aspects of building design and construction rather than a narrow specialized aspect of it. In the end, we are held responsible for everything from the building's structural integrity to its fire and life safety. Buildings also have to be aesthetically pleasing and functional, but that's a topic for another post.
My heart goes out to the people touched by this disaster, and it is my hope that we all learn from it. Building codes in Great Britain will be revised – you can bet on that.
...and as much as so many Americans love to hate the government, its important to remember that our government exists for very good reasons, as do most of the laws and regulations they enforce. Building codes and their enforcement are an excellent example of this - even if they are difficult to deal with sometimes.