Episode 30 – Not the Titanic

We’re up to 30 episodes of DisasterCast, and we still haven’t talked about the Titanic. Why start now?
This episode talks around the Titanic. We talk about icebergs, lifeboats, shipwrecks and radios, but not the sinking of the unsinkable.

The next episode will be about dangerous safety features – ways that people can or have been hurt by systems specially designed to keep them safe. If you have any suggests, post a comment to this episode, or use the feedback link above.

Transcript is now available.

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Episode 29 – Ethics and DC-10s

Safety engineering and management is full of compromises. We compromise between short term and long term risk. We compromise between absolute assurance and practicability. We compromise between blame and understanding. The one thing we can’t compromise is our professional code of conduct. Or can we? Should our actions be bound by a strict set of rules, or by their intended and expected outcomes? Is an action good because its what we would want if we were in someone elses shoes, or because it makes us into the sort of person we want to be?

And just how did McDonnell Douglas manage to stage two near-perfect dress rehearsals before a DC-10 crashed into the French woodlands?

Episode transcript is now available.

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Episode 28 – Level Crossings

This episode is all about level crossing safety. Level crossings are a simple situation, repeated throughout the world, that illustrate a number of important safety concepts. Through accidents such as Hixon, Lockington, Kerang, Langenweddingen and Fox River Grove we can learn lessons about human factors, dependability trade-offs, safety management interfaces and risk prioritisation.

Episode 28 transcript is now available.

The Introduction to System Safety course in Canberra, 7-11 April 2014. Let me know via the feedback link above if you’re coming along.


  1. The study of train drivers and heavy vehicle drivers mentioned in the episode
  2. The Hixon accident report [pdf]
  3. The Lockington accident report [pdf]
  4. The Kerang rail safety investigation report [pdf]
  5. The Fox River Grove Highway/RailRoad Accident Report [pdf]

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Episode 27 – Security and Safety

In this episode we talk about Stuxnet, and the relationship between safety and security more generally.
Stuxnet demonstrated that a determined cyber attacker could influence the operation of potentially hazardous industrial machinery.
Just how representative is Stuxnet? It required elite teams from at least one, possibly two countries, and achieved only minor damage.
Are we in danger of non-state actors causing industrial accidents using their home PCs? Maybe we should ask the 14 year old who derailed
trams using a rewired TV remote control …

Transcript is available here.

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Episode 26 – Battery Dangers

If you’ve ever wondered why safety is considered a systems discipline rather than simply a specialisation of chemical, civil, mechanical or electronic engineering, the humble battery is a great example. To a chemical engineer, a battery is an electrolytic process, with ions travelling from cathode to anode or vice versa, depending on what the battery is doing. To a mechanical engineer, a battery is a combined heat source and a container filled with hazardous substances. To an electronic engineer, a battery is a source or sink of electric power. In each role the battery is not a single component but is part of a variety of engineering systems. As a chemical reaction it is part of an atmospheric system. As a hot toxic container it is part of a physical layout. As a source of electricity it is part of a control or power system. For safety, we need to understand the battery as all of these things.

In this episode we’re going to discuss a number of battery hazards, along with some associated accidents.

Transcript is available here.

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Episode 25 – Feynman Gap

The Feynman Gap is the gulf between engineering understanding of risk, and management understanding of risk. The concept is named after Professor Richard Feynman – drummer, lockpicker, nobel prize winning physicist and member of the Rogers Commission investigating the Challenger accident.

This episode talks about the nature of the gap, what causes it, and what we can do about it.

The accident for the episode is the Hyatt Regency Walkway Collapse of 17 July 1981. The Hyatt Regency hotel in Kansas City featured a spectacular multi-storey open atrium, crossed by suspended walkways on each floor. During a dance competition on the 17th of July, 1981, the atrium was packed with dancers and spectators. The fourth floor walkway fell onto the second floor walkway, which fell into the crowd below. At the time it was the deadliest building accident in the United States, and it still holds that unfortunate title unless you count the collapse of the South Tower of the World Trade Centre.

In the final segment I update the discussion of Bicycle safety from Episode 22 to address the topic of riding two abreast or in the middle of the lane.

There’s a read-friendly version of the Hyatt Regency segement at dependablesos.org
The Feyman Gap segment will also appear shortly at dependablesos.org.

The rest of the transcript is available here.

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Episode 24: Reruns

DisasterCast is on hiatus until January 28. In the meantime, here are three segments from previous episodes.
This episode covers Three Mile Island, BA 5679, and Clapham Junction.

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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.


  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.


  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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