Human Error Part 1: De la Concorde Overpass

In September 2006, a bridge collapsed in Laval (a Montreal suburb), resulting in 5 deaths. An inquiry, the Johnson commission, is trying to understand this event and prior incidents.

As always, multiple factors are involved in this accident: bad design, shoddy construction, poor repairs and substandard construction materials. These factors are always boiled down to human errors: a design, planning, executions or maintenance errors.

The first most frightening errors are associated with the substandard preparation of the concrete.

The Canadian Standard stated in 1966 that for concrete, the ratio of water-cement should have been 0.47 or 0.54 depending on the type of usage. A higher ratio means a more fragile structure. It results in more porosity in the structure that may have more damaging consequence when submitted to rough weather over the years.

1) Engineers from Desjardins Sauriol either ignored those standards or were over confident with the security factors. They used 0.56 ratios, which is just over the superior limit.

2) Even more, the 1967 Canadian standards are seriously questioned by Jacques Marchand from the University of Laval, in a report requested by the Johnson Commission.


Human errors

Everybody knows humans make errors. But humans rarely make errors on purpose or with bad intent. Humans make errors because of subtle and invisible psychological mechanisms that are either at the:

  • Skill level: for example a typo
  • Rule level: application of the wrong rule
  • Knowledge level: not having the right information or the right knowledge stored in long-term memory
  • Meta cognition level: Humans develop strategies (wisdom) to circumvent their cognitive limitations in judgment, attention, and memory. For example a good inspector will wait to have all information on hand before making a judgment. He knows if he doesn’t, he might be anchored by his first impressions. Banks know that bankers are biased and could be influenced by the client. So decisions to accord loans are performed by a separate group of risk managers.

Not knowing the standard is a rule based on error. It can be explained by a lack of knowledge or information about the existing standards. By cognitive task analysis (analysis of the thought process), root cause can be identified and strategies can be devised to prevent those errors.

Being overconfident with the standard is a lack of wisdom or more formally a meta-cognition error. It is much more frightening error because if wrong, hundreds of bridges and structures could be affected.

History teaches us that regulatory agencies make errors and standards are updated with new knowledge. Even physics’ laws are updated over time with new discoveries. A bridge is an open system. Many things can go wrong during construction: poor soil analysis, poor material preparation and selection, construction workers not following the plan. Things can change during years of usage: weather, salt and abrasiveness, load on the bridge.

In the beginning of the 20th century, constructions (bridges, overpass, equipments) were solid and built to last while paradoxically engineering knowledge was limited. For this reason, security factors used were much greater.

In the 60, 70, engineers believed they could master nature and were overconfident with standards (lack of wisdom). While standards have been improved, they are maid by the same organisms with the same methods. Engineers still believe in those new standards today. Sadly, engineers today are trained in the universities to calculate and apply rules, not to question. Later, in their senior years, they are trained to ensure they will not be sued.

In reaction to the Johnson commission, we hear comment such as: “it will be costly to inspect all those bridges” or “I was not responsible of the maintenance, the city was responsible”. Wake up, we are not talking about money or who should be blamed, we are talking about security! What will be the cost if everybody is frightened that another bridge would fall? Those reactions are certainly not a manifestation of wisdom.

Solution one: standards should become guidelines. In case of an accident, engineers will always be accountable event if the guidelines are proven wrong. Consequently, engineers will ask more questions and might use higher security factors.

The second most frightening factor is the competency of authority.

There is conflict of interest at the MTQ (ministry of transport of Quebec) because, under the same ministerial budget, they are in charge of building, maintaining and inspecting. If the budget is low, they might be tempted to allocate more budgets on new stuff. This will result in neglecting existing work or worst, neglecting inspection tests because they are costly. Sounds familiar? That is exactly what happened for the la Concorde Bridge.

Solution 2: Separate jurisdictions for inspections. This independent jurisdiction should have full power to close a structure or a bridge. With this separation, hopefully, we should avoid conflict of interest and judgment errors such as the one in de la Concorde Overpass.


7 thoughts on “Human Error Part 1: De la Concorde Overpass

  1. I have a philosophical approach for that kind of problem. I think we need the past to learn about the future. My point is that we learn from our mistakes. It is impossible to anticipate without significative facts coming from the past. Purpose is part of the future. The past is the background which we can have to support our ideas and mental representation.

    The second point is: error is a fundamental aspect of knowledge. By making mistakes one can learn what is wrong. In a certain way, efficiency is connected with error.

    I think efficiency is important for specific tasks but is less important for others depending on imagination (arts).

    The question is are we serving efficiency? if yes…why?

  2. I agree with you Marc, Human learn from errors and human do errors. Although in de la concord overpass story, Engineering accumulated thousand of years of trial and errors. They had a lot of prior significant facts.

    For your second point, it is very true. We learn form mistakes. In Design that is exactly what we try to do, provoke those mistake ahead of time with simulation, laboratory study. This help prevent bridge from falling.

    1. Did you happen to noicte in the first shot, about 1/3 of the way over from the right, just above halfway up, it looks like a pair of eyebrows and eyes, on a flat face, looking down? Like some huge alien inspecting the landscape. This is a great cloud shot, especially in the HDR mode. Did you take any out away from the bridge?

  3. Golly, when I used to live on Capitol Hill, I walked to Downtown quite frenueqtly (the Paramount was particularly easy, as I recall), and it didn’t seem to be a problem. I do agree that the intersection in question was not the best, but as a pedestrian, one must develop somewhat of a philosophical attitude, and be ready to vault 1 1/2 foot high curbs in the midst of traffic. A similar approach is necessary for biking in many areas of most cities.

  4. We could several volunteers along with opening a brand new system in the community. Your on line site provided us with beneficial information to function about. You’ve accomplished an impressive work and our overall community will probably be grateful to you personally.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s