A Historical Marker

by Don Friedman on March 21, 2017


This is a sign on the door of a deli near our office.* (Click to enlarge.) It is a reminder that not only is it illegal for businesses to prop open their front doors while they run air-conditioning inside, but that there is a mechanism for people to complain about businesses that air-condition the street.**

Joel Spolsky has a great blog post – from 17 years ago! – on the topic of historical markers embedded in current contexts. He gives an example that perfectly lines up with that door sign: if you see a sign in a diner that says that knapsacks can’t be put on the counter, it’s there because people used to put their knapsacks on the counter. Those signs are showing up on doors because it used to be common for small retail businesses to leave their doors open in the summer. It wasted electricity, but it made their stores more enticing for sweating passers-by. Joel, being a software designer, then goes on to discuss this phenomenon in terms of software design; I’m a structural engineer, so I’ll discuss it in terms of buildings.

Part of the issue is learning from past mistakes. But there’s more to this topic than that. Past successes can turn into mistakes over time. Look at fire escapes. They were introduced in the nineteenth century as a way to have an egress path that wouldn’t burn: in buildings with entirely flammable wood interiors, the way to achieve that nonflammable egress path was to put it outside the building. They were once considered to be such a good idea that they are one of the few changes in building technology that was not accompanied by grandfathering of the existing conditions: owners of existing buildings were forced to install new fire escapes.

Over time, it has become clear that fire escapes are not so great. They are difficult to walk on safely, particularly if the people walking on one are in a panicked rush. The standard design – written in the New York State Multiple Dwelling Law, and so difficult to get away from – has no redundancy and therefore will become unsafe with only small amounts of damage. Most importantly, the wrought iron of the fire escapes has shown an unsurprising tendency to rust where it passes inside the masonry of the exterior walls. When we perform facade inspections, we see problems with fire escapes all the time. Given the gradual decline in the frequency of major-building fires*** I’m not sure that, in 2017, fire escapes are saving more people than they’re hurting. Obviously they’re not going away any time soon, but our perception of them has changed as the historical circumstances that made them a good idea recede further into the past. But meanwhile, fire escapes remain on most of the streets in Manhattan, as a visible marker of the history of egress.



* To be honest, in the same building as our office. This is not the laziest I’ve ever been, but it’s in the running.

** The complaint option is a bit odd. The average pedestrian loves when businesses break this law in the summer, as it makes walking down the street a lot cooler.

***  Due, at least in part, to improved fire detection technology and to improved inspection of buildings for fire hazards.

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