The Grenfell Report

Trigger warning: there is a lot of discussion of people dying at the links and some below.

The “phase 2” report on the Grenfell has recently been published by the official inquiry panel: here. The New Civil Engineer has a good short summary here: “Grenfell disaster: ‘culmination of decades of failure by government and construction industry’” In one sense there are few surprises in the thousands of pages of the report: the fire was seven years ago, and the cause was apparent almost immediately. If you wrap a high-rise building in flammable cladding, a fire will go from contained within one apartment to covering the entire structure with terrifying speed. If you have inadequate compartmentalization and egress in a tall building, a fire will lead to a lot of deaths.

I cannot emphasize enough that I am not pointing a finger at the UK or its regulation of building, because similar problems exist everywhere. As a matter of fact, I’m going to switch most of my discussion below to NYC history because I’m more familiar with the specifics. I spent a lot of time on the research for The Structure of Skyscrapers reading about long-ago disasters.

We don’t necessarily think of construction history as a series of technological regimes, but that viewpoint is useful for understanding what happens when we change how we build. Up to the end of the nineteenth century, the vast majority of buildings were constructed in a technological system composed of wood beams with cut-and-pinned joints, solid brick walls, plank floors, brick vaults, and so on. It was not designed in the modern sense, it was developed mostly by trial and error over a long period of time, and had regional variations based on the climate and availability of materials. New technology began to show up in the US in the middle third of the 1800s: cast iron on the scale of a building column or beam, wrought iron on the scale of flitch plates or channels.

By the late 1880s, enough new technology had been developed – steel beams, relatively lightweight fire-resistant terra cotta floors – that buildings started to act in different ways. Having some iron beams doesn’t change the fundamental nature of a building, but having “fireproof” floors does. Because of misunderstanding about the way cast-iron columns work, there were a series of horrific building collapses before iron was abandoned in favor of steel. The fireproofing of structures gradually improved, with, again, a series of horrific fires showing ways in which the newly-developed technology was inadequate. The Triangle fire in 1911 marks the end of the first era of modern fireproofing: the fireproofing there worked just fine to protect the building from structural damage. It did not protect the workers in the Triangle factory, who died because of inadequate egress. The focus then switched to egress, and by 1920 we had egress code provisions something like what are used today.

At every step in the development, new technology moved ahead after the old “new technology” failed, usually killing a bunch of people in the process. And then, starting in the 1950s, there was economic pressure to change the technology again. To be clear, the way that buildings were constructed and fireproofed in the 1920s still works today (some small details would be different), but it was heavy and relied on significant amounts of labor (like masons for terra cotta fireproofing). We switched from concrete slabs in steel buildings to concrete on metal deck with spray-on fireproofing to save money (no more carpenters to build formwork) and weight; we switched from masonry walls to glass and metal panels for architectural style, and to save money and weight.

There are always tradeoffs. For example, spray-on fireproofing is as good at providing heat insulation as masonry, but it is not as physically tough. I think an instructive comparison is the progress of fire in 7 World Trade Center and 90 West Street on September 11, 2001: the first was a 1980s steel-frame building and the second is a steel-frame building from 1907. Both were set on fire at multiple locations by flaming debris from the collapse of 1 and 2 World Trade center; 90 West had little structural damage (its north facade and interiors were pretty well destroyed) because the fires were limited by the intact terra cotta fireproofing, while 7 WTC collapsed from the effects of its fire.

Economic pressure pushes designers and builders towards lighter and newer materials. They are tested before use, but testing never gives an exact view of what will happen in a real fire. (It appears that the flammable cladding at Grenfell may not have been properly tested for the configuration in which it was used.) But to some extent using new materials resets the clock: the past disasters which our codes are based on used different materials and systems. An unpleasant way to think of it is that we have to have new disasters to point out the problems with the new technology. If we try to avoid that, we can never try new technology, which is also a bad outcome.

There’s no grand conclusion here. Fire-spread at building exteriors, particularly tall buildings, is well established. So any material or system proposed for use there needs close examination. Ditto for the partitions around interior shafts. You can put two fire-separated stairs in the space of a single stair by using a scissors configuration, so building a tall building with a single stair seems to be unlearning some old lessons. Depending on the size of the building footprint, more than two stairs may be needed. But beyond these simple ideas: there is no miracle product, no magic system that makes buildings safe, so pay attention to how materials and systems fail.