Is there a connection between fatal and non-fatal accidents, or is it a fallacy to focus on the minor potential events with the hope of managing the major events?
Today’s study explores these relationships based on 23k reported serious accidents in the Netherlands.
Ref: Bellamy, L. J. (2015). Exploring the relationship between major hazard, fatal and non-fatal accidents through outcomes and causes. Safety Science, 71, 93-103.
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Transcription:
Think about the routine incidents in any high-risk environment. A tiny gas leak, a minor equipment malfunction, a brief loss of control. We often treat these as isolated events, easily managed. But what if there’s an unseen but rather simple thread connecting those minor occurrences directly to the devastating catastrophes, a connection we’ve simply failed to grasp?
G’day everyone, I’m Ben Hutchinson and this is Safe As, a podcast dedicated to the Thrifty Analysis of Safety, Risk and Performance Research. Visit safetyinsights.org for more research.
Today’s study is by Linda Bellamy, titled “Exploring the Relationship Between Major, Fatal and Non-Fatal Accidents Through Outcomes and Causes,” published in 2015 in Safety Science.
It explored the critical link between major hazards in both fatal and non-fatal accidents. To do this, the research analyzed over 23,000 serious occupational accidents and the number of fatal and non-fatal accidents from the Netherlands, between 1998 and 2009.
This extensive data was analyzed using a specialized tool called StoryBuilder, which used hazard-specific bowtie diagrams to map out accident causes and effects. The study’s core goal was to directly investigate any connections between minor and major accident scenarios.
So as a bit of background, major accident investigations often reveal that organizations have types of blind spots and overlook, in hindsight, warning signs leading to accidents incubating in the background. And complex systems have been argued to have a type of inherent potential danger. However, unlike those massive, high-profile events that make national news, everyday occupational accidents, even those with multiple fatalities, rarely get the same public attention.
The academic discussion on accident relationships has also been quite divided. Earlier research suggested that smaller accidents are symptoms of bigger problems, implying that fixing small ones may help to avoid some of the larger ones. Conversely, more recent views, especially after major industrial disasters like the Texas City refinery explosion, argue that occupational injury stats are not reliable indicators for process safety performance, suggesting a complete disconnect.
Andrew Hale in 2002 even stated that “Assuming preventing minor accidents automatically prevents major ones is based on careless and unsupported reasoning.” Bellamy’s study directly tackles these differing viewpoints head on.
So what did they find? Well, the analysis of those 23,000 serious accidents revealed a crucial insight: smaller, more frequent accidents can provide valuable information about the causes of bigger, rarer catastrophic accidents. But only if you’re looking within the same hazard category.
So 36 hazard categories were explored in this research, including a range of things, but the hazard categories like explosions, falling objects, electrical contact and more. This finding directly contradicts the idea that personal and process safety are totally unrelated. Instead, Bellamy’s research concludes that there is a link between occupational and process safety, and between fatal and non-fatal occupational accidents. And that link is the hazard.
Here are some other key results:
- Commonality in causal or contributing factors: There were no fatal accidents in this sample. There was no barrier failure caused unique to fatal accidents that hadn’t also occurred in non-fatal accidents. This strongly suggests that less serious accidents of the same hazard type can indicate potential for more serious events.
- Lethality versus frequency: The study used “accident ratio hills,” which will make more sense if you actually read the paper. This shows how hazards differ in their outcome severity. Interestingly, the most lethal hazards, like drowning, are not necessarily the biggest killers overall. For instance, falls from height or contact with falling objects cause far more serious and fatal accidents overall, even if other hazards might be statistically more lethal per incident.
- Correlation with hazard types: While overall, general lethality didn’t correlate with the accident numbers, a significant positive correlation was found between non-fatal and fatal victims within the same specific hazard types. This is largely due to the common element of exposure to the hazard.
- On barrier failures: Fatal and non-fatal accidents often share the same underlying barrier failures. But these failures don’t always occur in the same proportions for different severity outcomes. Importantly, there is no one fatal barrier failure cause which has not also occurred in the non-fatal accidents. This suggests a role in breaking down incidents at a barrier level.
So what can we make of these findings? Because the underlying contributing and causal factors and barrier failures for the same hazard accidents can be similar, investigating minor, frequent incidents for their high severity potential and fixing those specific safety barrier problems could help prevent bigger, more severe incidents of the same type. It’s not enough just to look at the frequency. Hazards and their barriers need independent, deeper scrutiny.
Also, they provide examples of accidents and the types of barrier failures. One is the AmeriCentral gashole collapse in 2003. Now, very quickly, this multi-fatality accident’s underlying contributing or underlying causal factors, like deficient design and anchoring, were also found in the less severe non-fatal scaffold accidents in the database. This case study and others illustrate that the causal and contributing factors of major incidents are often mirrored in seemingly minor ones when the hazard type is the same.
When I think about this, I think there’s a clear finding that there can be a connection between fatal and non-fatal, and that connection is the hazard type. Of course, other work, and more recent work, like that from the Hale and Ellen team, provides nuance around the magnitude of energy and more, suggesting there might be some differences. But simply put, focusing on the hazard scenarios should be one key focus. A slip hazard may not be seen as fatal, but if it’s at height in that scenario, then it becomes fatal.
So what were some limitations? It’s vital to remember that this study, like any study based on accident data, has limitations. The information comes from, in essence, hindsight investigations, which are always subject to investigator biases and filters. For example, regulators often focus only on the most severe or legal breaches. Also, and this one I think is really prevalent, is that what’s listed as a causal factor depends on the investigator, and their own mental models, and the accident models that they use, and any reporting taxonomies that they follow, and a whole range of other pressures and influences. Again, what you look for is what you find.
That’s it on Safe As. I’m Ben Hutchinson, and I hope you found this useful.
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