Episode 23 – Preflight Briefing

This episode discusses a few aspects of preflight briefings on passenger aircraft. In particular, we look into accidents and evidence relating to lifevests, oxygen masks, and brace positions.

Transcript is available here.

References

  1. Miracle on the Hudson Accident Report
  2. Flight ALM 980 Accident Report
  3. Stansted Incident Report
  4. Virgin America Safety Video
  5. Air New Zealand (Middle Earth) Safety Video
  6. Air New Zealand (Fit to Fly) Safety Video
  7. Thompson Safety Video

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Episode 22 – Bicycle Safety

This episode addresses seven questions about bicycles and safety:

  1. How dangerous is cycling compared to walking or riding in a car?
  2. Does cycling actually get safer as more people cycle?
  3. Should cyclists wear helmets?
  4. Are most bicycle accidents caused by cyclists riding dangerously?
  5. Why is it so hard to create decent bike lanes?
  6. How dangerous are bicycles for pedestrians?
  7. What’s the deal with those cycle airbags?

Episode transcript is available here.

References

  1. A Case-Control Study of the Effectiveness of Bicycle Safety Helmets – This is a good example of a case control study on the effectiveness of helmets. Link is to the abstract – subscription needed to access the full article.
  2. Nonuse of Bicycle Helmets and Risk of Fatal Head Injury – Another good example of a case control study. Full text of this one is freely available.
  3. Bicycle helmet Efficacy: a meta-analysis – This freely available article gives a fair summary of the overall evidence for bicycle helmets, including the neck-injury issue.
  4. No clear evidence from countries that have enforced the wearing of helmets – A fair summary of the impact of helmet laws on safety (freely available)
  5. Bike Lanes versus Wide Curb Lanes: Operational and Safety Findings and Countermeasure Recommendations [pdf] – A good example of video camera studies of cyclist behaviour and the way cycling infrastructure changes this behaviour
  6. Bicycle Helmet Safety Institute review of the Hovding – this is the fairest review I found of the bicycle airbag system.

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Episode 21 – Safety Integrity Levels

What do electric cars, steel capped boots, and balloons bursting in crowded lecture theatres have in common? Not much, except that they all feature on this episode of DisasterCast. When it comes to achieving safety, one of the key questions is “How Much is Enough?” There will always come a point where the amount of risk you are facing doesn’t justify taking further measures to reduce it. Beyond this point, we can receive better return on our safety investment by spending our efforts and money elsewhere. We may even be destroying the benefits we get by trying too hard to be safe.

When we’re designing systems, certain aspects of safety can be expressed in numbers. This is particularly the case when we are concerned about random failures. Random failures are what we usually think about when we consider a car, train or aircraft breaking down or doing something unsafe. One minute a component is working, then it fails, after which it is no longer working. We can express the random side of things as a probability. We can reduce the likelihood of random failures by using better components, and we can reduce the impact of random failures by building redundancy into our systems.

Random failures aren’t the only type of failures though. We call the other sorts of failures “systematic”. Redundancy doesn’t help here, because no matter how many widgets we have, if they’ve all got the same design flaw then under the wrong conditions they’ll all fail at once.

Working out how much redundancy we need is something we can determine mathematically. Working out how much protection we need against systematic failures is more nebulous. Software is a good example of this. We never know how many errors there are in a piece of software, because any time we find an error we fix it. We can reduce the number of errors by putting a lot of effort into finding and fixing them, but this still doesn’t help us count them.

The question “How safe is safe enough?” turns into “How hard do I need to keep looking for systematic failures?”. This is where the concept of safety integrity levels comes in.

Partial transcript is available here.

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