[Note that this article is a transcript of the video embedded above.]

The idea is simple: If there’s a fire in a tall building that blocks the main stairwell, people need an alternative way to evacuate, preferably one that is somewhat protected or at least far away from where the fire is happening. If you’re in a one or two story building, it’s pretty simple: just get out of any window or door. You may get hurt a little, but you’ll still be away from the fire. In the denser cities of the early United States, though, as the buildings grew taller, the options for evacuation became more complicated. High-profile, horrific building fires were a nearly constant plague in factories, tenements, office buildings, and theaters. The external fire escape seemed obvious to many: Bolt a metal staircase to the outside of the building with a landing below a window on each floor.

Fire escapes became an element of American culture in many ways beyond simple safety equipment. They serve as dramatic devices in films and plays, provide a scenic place for urbanites to get some fresh air, and they impart a quintessential character on the skylines of our oldest cities. But it turns out that we’ve pretty much never agreed on how well they actually work (if at all) or whether they were ever the right solution to the problem. And while many older buildings still have the original ones installed and maintained, they’ve slowly started disappearing. The story of their decline is a fascinating case study in how building codes actually work. I’m Grady and this is Practical Engineering.

An important thing to keep in mind about any safety devices in buildings, including elaborate metal contraptions that serve as fire escapes: owners don’t just install this stuff out of the goodness of their hearts. And I don’t mean that as a dig on the owners. It’s just very difficult to weigh the costs and benefits of safety devices that, honestly, might never even be called on to function over the lifetime of the building. The economics of real estate just don’t incentivize going above and beyond, or really much consideration at all of low-probability, dangerous situations. Building safety is rarely a primary factor in purchasing decisions for tenants, so it doesn’t hit the bottom line on a landlord’s balance sheet. It sounds like cold-hearted capitalism, and in many ways it is, but of course, there’s another side to this coin. You could cram so many sprinklers and fire alarms into a building that there’s no actual space to live or work in, and nobody could afford it even if they could squeeze in.

So obviously, there is some reasonable line between no safety at all and overkill. And it doesn’t make sense to put the burden of drawing that line on every individual building owner or even every individual architect and engineer who designs them. This is the entire purpose of building codes: they’re an (ideally) well-informed consensus around what’s quote-unquote “worth it.” It’s society’s way of taking responsibility for the safety of our constructed environment.

That’s exactly how fire escapes came into being in the first place. In major American cities like New York, Boston, and Chicago, we began building tall, multi-occupancy residential buildings around the mid-1800s. And they weren’t like the apartments and flats that are the baseline standard today. Multi-family housing, called tenements, were almost exclusively built for poor immigrants and laborers. They were designed for efficiency, cramming as many units as possible into a single building. And as early as the 1860s, cities started recognizing the issue of fire safety. Smoke and flames seek open vertical shafts where hot air can rise quickly, and the stairways in tenement buildings provided the perfect conduit. With lots of people, combustible materials, and often a single open stairway, these buildings were dangerous fire traps.

In February 1860, a bakery in the basement of a six-story New York City tenement caught fire. Flames quickly spread upward, but the fire department’s ladders could only reach up to the fourth floor. Ten people lost their lives, because there was no way to escape the building. The press coverage that followed catalyzed a public outcry for reform. The fire forced the city into action. Working with the state, they passed “An Act to Provide Against Unsafe Buildings in the City of New York,” which required a fireproof stairway or some means of exterior escape on all tenement buildings. The law was retroactive, meaning even existing buildings were required to comply. And that decision shaped the design of fire escapes perhaps more than anything else in their history.

Reconfiguring a stairway inside an existing building is an enormous endeavor. It’s costly, time consuming, and disruptive, if it’s even feasible at all. For many building owners, that just wasn’t realistic. The alternative was much simpler and cheaper. So that’s what most did. In reality, enforcement of the new law was lax, so many buildings didn’t comply with the new rule at all, but where buildings were upgraded, it was almost exclusively to facilitate egress on the outside.

The rules for alternative egress routes would be extended to other types of buildings over time. But they weren’t very specific about what form those escape structures should take or if a “structure” was even necessary at all. So inventors got pretty creative. All types of rope and chain ladders, chutes, slides, slings, baskets, and tubes were proposed. For a time, New York City building officials accepted just about any type of escape device as compliant with the law. One of my favorites is the parachute hat you could keep stored in a closet by the window, along with rubber overshoes to soften the inevitable hard landing. I doubt anyone took this seriously, even at the time, but you have to wonder if the inventors actually tested some of these wacky ideas.

The other large cities mostly followed New York, requiring some kind of alternative escape route on tall buildings in the event of a fire. And eventually the classic iron or steel ladder-and-balcony system coalesced as the default solution to fire escapes in the early 1900s. It definitely seems like a better system than some of the others being proposed at the time, but not everyone was convinced.

Even before the skeleton-style fire escapes became somewhat standardized, Americans were trying to apply some scientific thinking to the problem. You have to realize that building regulations are, by necessity, kind of onerous. If people were doing these things already, there would be no need for the rules. Practically every aspect of the urban environment looks the way it does because of the codes enshrined by some committee or group of professionals in what’s usually a fairly opaque process. They’re blanket requirements that often affect every single building, they’re expensive to comply with, and they have wide-ranging effects that literally shape the city. So it’s important that we get this stuff right.

One of the first technical considerations of the modern fire escape was carried out by the Franklin Institute in 1881 after the Randolph Street mill fire in Philadelphia trapped 35 people inside. Their conclusion was that external egress paths, in other words, the bolt-on fire escapes had, quote, “comparatively little value.” They recognized the fact that it was the only practical choice in some situations, but that internal stairways, properly constructed, afforded the best means of escape.

Decades later, their conclusion and recommendations were made clearer in one of the most famous and also worst industrial disasters in American history. In 1911, the Triangle Shirtwaist garment factory caught fire in the top floors of the Asch Building in New York City. The building was out of compliance with the exit laws of the time. The doors in the narrow, winding staircases opened inward, making them hard to open in a crush of panicked people trying to escape, and one of them was reportedly locked. The building had an exterior fire escape, but it buckled under the weight of fleeing garment workers, dropping them to the ground below. Ultimately more than 140 people died in the tragedy, most of them women and girls. Among the many reforms that resulted was showing how a fire escape could do more harm than good.

This debate continued for decades. One side said, essentially, we should not be using these external fire escapes. A report in the National Fire Protection Association’s quarterly journal called them, quote, “a pitiful delusion,” saying that they “contributed to the principal element of tragedy to all fires where panic resulted.” The worry was that the widespread use of these iron escapes was just making it harder to enact regulations that would be more functional. That organization eventually released a model building code that recommended prohibiting outside stairs as fire escapes in 1923, but it wasn’t widely adopted.

The other side said that, since external escapes are already so widely used, we should be focused on making them better. The 1949 National Building Code, which was largely developed by insurance companies, took a more pragmatic approach, allowing exterior escapes but regulating them with minimum sizes. Basically they made them into full outside stairways as robust and large as the ones inside. But by then, the list of disadvantages of the traditional fire escape had just grown too long:

Architects didn’t like them because they cluttered up a building’s facade, sometimes even blocking views. They could make burglaries easier, giving anyone nefarious access to the upper floors of a building. They required a lot of maintenance to prevent rust and maintain stability. No one really practiced using them, so they were rarely the first inclination in an actual emergency. Even if they were used, the bottom stairway, which was often hinged up to avoid intrusions, was sometimes inoperable from lack of regular use. They weren’t suitable for many types of buildings, like hospitals, where getting people through a window or down a steep staircase is a challenge. And, as nice as they sometimes are for tenants to have a little balcony, it is difficult to preserve their function as an actual egress route. It’s unused space, after all, so people naturally take advantage of them, putting furniture or using them for storage, blocking that path if it’s ever needed.

The only real advantage is that they didn’t take away from the expensive interior floorspace, but that just wasn’t enough of a benefit anymore. When New York City updated their building codes in 1968, exterior exits were officially prohibited for new construction. Many other large cities across the country had either already banned them or would follow soon after. What took their place? The exact thing the Franklin Institute proposed in 1881, nearly a century earlier. I have to read this quote because of how prescient it was:

“As a general rule, applicable to all buildings, the main reliance should be placed upon stairways in daily use, for the obvious reason that the occupants of a building instinctively seek such an escape in case of fire, that they are familiar with it, and that, being in daily use, it is reasonably certain to be unobstructed and to have the approaches to it clear.”

Even more than that, they suggested that stairways be enclosed in brick, built of incombustible materials, and have self-closing doors to keep out smoke. And that’s practically a perfect description of the modern tower stairway used in tall buildings today. And you might not even notice it. All the safety features are a lot less conspicuous than a spindly iron assembly bolted to the outside of the building, but we’ve just found that it’s so much safer. And it really took these gradual improvements over decades to reach this consensus: safer consumer products, fire rated building materials, sprinklers, alarms, and even reliable air-conditioning systems that make windowless, interior, smoke-proof stair towers possible.

And that’s kind of the story of lots of building codes. They have this weird momentum. For one, they normally only apply to new construction, so they’re kind of like planting a tree. We don’t see the benefits until years later. But once they are in place and the industry evolves to accommodate those regulations, there’s a lot of resistance to getting rid of them later. So it can be really hard to imagine the repercussions a specific code will have years into the future. Here’s a perfect example:

The Center on Building in North America recently completed a report on elevators, finding that they cost at least three times as much as those in other developed countries around the world. One of the reasons for this is just that they’re much bigger in America. And the reason for that is one fire inspector in Glendale, Arizona submitted a proposal to the International Code Council to require elevators fit a horizontal stretcher, erroneously stating on the form that there would be no cost impact. At face value, this is sensible. If you have a medical emergency high up in a tall building, it would be ideal if the first responders could use the elevator to get you down.

The amendment slipped through without close scrutiny, and now, if you want to put an elevator in your building in the US, it has to be a big one. But the result of that change wasn’t only that our elevators got bigger, but also that more and more building owners now just decide it isn’t worth the cost at all, opting for walkup designs instead. So the change actually led to fewer accessible buildings, and ultimately hurt the very people with mobility issues the rules were originally intended to protect.

In a similar way, New York City’s first fire egress law in 1860 applied to existing buildings as well as new construction, essentially ensuring that the prevailing solutions were going to be bolt-on retrofits to the outside of buildings, and that momentum carried for practically the next century and a half. Writing building regulations is a messy process, and there really is rarely a single “right” answer. There are just tradeoffs that affect every building differently and ripple through space, time, and the economy. There’s something nostalgic and charming about the old iron fire escapes across American skylines, but I think it’s probably best that they’ve finally gone the way of the parachute hat.