Atlanta Burns a Bridge

For several years—possibly since 2006, according to one report—construction crews working near an elevated section of Interstate 85 near Piedmont Road in northeast Atlanta had stored large quantities of bright-orange high-density-polyethylene (HDPE) pipe.  It's used for a variety of things in public works, such as conduits for streetlight and traffic-signal cables, and comes in large reels two or three feet high each, that were stacked two high under a bridge span.  It's not the kind of thing one could just shove in a backpack and walk off with, so authorities thought that just surrounding the stash of pipe with a chain-link fence was enough security.

Last Thursday, March 30, a fire was reported under the span, and despite desperate attempts by firefighters to combat the fierce heat for over an hour, several emergency responders barely escaped with their lives when the span over the pipes collapsed, damaging both northbound and southbound parts of the interstate to the extent that it will be closed for several months for repairs.  Eyewitnesses reportedly saw Basil Eleby, an apparently homeless man, standing on a chair in a shopping cart near the fence shortly before the blaze, and Eleby is now in jail, unable to post $200,000 bond and awaiting trial for arson.

Fortunately, no one was killed or injured in the fire or collapse, but Atlanta commuters are going to have to deal with serious disruptions, as that part of I-85 is the main transportation corridor between downtown and the northeastern suburbs, normally carrying over 100,000 cars a day.  It was how I would get downtown from the suburb of Chamblee during my two years working as an engineer at Scientific-Atlanta, and I can only imagine the traffic snarls that this will cause.

Clearly, nobody expected this to happen, and for over a decade it didn't happen.  Those pipes have been sitting there at least that long, and as far as accident-prevention policies are concerned, it didn't look much like an accident waiting to happen.  Of course, arson isn't an accident, but it's unlikely that Mr. Eleby had any idea what would happen if he tried to set those pipes on fire.  It's too early to know what his motives might have been, but even if it turns out that he was hoping to cause major damage, I doubt that he really expected to bring down a bridge span single-handed.

One good thing that could result from this fire is that construction organizations everywhere will now view large accumulations of HDPE pipe with a different attitude.  It's not as dangerous as big piles of ammonium nitrate, which is known to be a powerful explosive under the wrong conditions.  But HDPE is a little bit like solid gasoline, in that it's just concentrated carbon and hydrogen with convenient air holes in it to aid combustion, and it's not surprising that a large stack of such pipes burned so hot for so long. 

It's far from criminally negligent to store that much flammable pipe under a vital transportation artery, but it wasn't the smartest thing to do, either, especially in an area where homeless people tend to hang out.  For complex sociological and economic reasons, many highway overpasses in major cities across the U. S. have been informally colonized over the past few decades by people who don't have, or don't wish to have, any other place to stay that will keep the rain and sun off.  Most of the time, the worst things these folks do is deal drugs, harass passersby, and leave messes, but now and then they can turn to more consequential criminal activity, such as the apparent arson that brought down the I-85 span.

I'll leave it to the civil engineers who will no doubt be combing through the wreckage to figure out exactly how hot a bridge has to get before it collapses.  But if steel was a significant component of the bridge—and it had to be, either as the main support or as rebar in concrete—well, steel melts at a certain temperature, and well before that it gets soft enough to lose most of its tensile strength, and there goes your bridge. 

Like many isolated mishaps that don't fit the usual patterns, a number of individually common events and conditions had to come together to cause this fire.  Both homeless people and construction supervisors see otherwise wasted public land under overpasses as a good place to take advantage of, either for living space or for storage.  And in secure warehouses, HDPE pipe is no more hazardous than furniture or wooden forklift pallets, which are notorious for burning fast because of the combination of flammable material and openings where combustion-aiding air can get in.  The chain-link fence around the pipes apparently kept intruders out for the ten or more years the pipes had been stored there, and there was no obvious reason to be concerned that some disgruntled or mentally deranged person would come along and try to damage the pipes.  But he did.

This fire, as bad as it was, could have been much worse.  It lasted long enough for first responders to isolate the area and stop traffic along the highway, keeping commuters out of harm's way.  And while fire-department personnel were unable to put out the fire before the span collapsed, at least no one was injured in the collapse.  Still, it would have been nice if they could have extinguished it before it got so widespread that it endangered the highway bridge overhead. 

Maybe it would be a good idea to install remotely monitored fire alarms in every big pile of HDPE in a public place, especially if it would cause serious damage if it caught fire.  True, there might be an issue with false alarms.  But I bet Atlanta's first responders would have been willing to put up with a few false alarms in order to prevent something that's now going to be a serious inconvenience for millions of drivers, and a multimillion-dollar expense for the taxpayers.  Next time you're in Atlanta, your best bet in getting around may be their MARTA trains, at least until they fix I-85.

Sources:  I consulted a number of news reports on the fire, including one on the Atlanta Journal-Constitution website at http://www.ajc.com/news/traffic/here-are-answers-your-questions-about-the-bridge-collapse/ZF0mtVvi7jedImZYKP7FuN/and Atlanta's Channel 11 News at http://www.11alive.com/news/what-was-burning-under-the-i-85-overpass/427257767, as well as the Wikipedia article on HDPE.