Workshop Wednesdays – The psychology of incidents

Friday 6 July 2018

When Derek Jones mentioned the idea of several related articles looking at the psychology of accidents, I wondered how we might make this fit in with our usual content genre. Over the last couple of years, we have had quite a number of safety-related pieces and also some in-depth ones on health and maybe that is the place to start: understanding the difference between 'health' and 'safety'. To look at the psychology of accidents, or as many professionals prefer – incidents, we need to understand the difference.

Health and safety defined

Sadly, the phrase 'health and safety' is overused, misused and misunderstood. We really do need to treat the two words as just that, two independent words. Consider generally safety to refer to physical integrity: for us woodworkers not chopping fingers off with circular saws, not losing fingertips to a chisel edge or an eye to

a flying grindstone fragment. Consider health to be about wellbeing, the adverse effects typically as the

result of an exposure to something and this can be over a short period when the effects are considered to be 'acute' or longer term when we talk about 'chronic' effects. These exposures could be dusts, chemicals, noise, vibration, stress, musculo-skeletal or repetitious injury.

Now the big difference between the two can be an individual perception of how big a threat something poses. The perception of threat, or usually we say risk, can play a huge part in how that individual then behaves and much research is ongoing into the area of 'risk-taking behaviour'. How one person 'sees' or perceives and considers a possible threat or risk is influenced by many things. Age can be a big factor but not in itself, simply that many other factors can bring influence over the years as we get older and experiences can be negative as well as positive. In a work situation the following may be significant factors in how we view things:

1. Experiences – whether or not unsafe behaviour resulted in injury

2. Training and education

3. Age and physical condition

4. Stress

5. Peers – workmates/colleagues

6. Personal interests

7. Job satisfaction

[n>8. Home life

9. Ambition

10. Job security

Defining hazards

With safety, many hazards can be obvious, either to see, or to be explained leaving little doubt about the potential. Having a hazard explained and the precautions to take can result in some people doing just that, to the best of their ability: more on that ability later. Some people will brush aside the problem and the most common remark I've had over the years is, “I've been doing it like that for 'X' years and never had an accident!” Unfortunately, having a negative experience also does not always change behaviour and I well remember having sharp words with a joinery company owner/employer about circular saw safety. He proudly told me he knew all about this and held up his left hand to demonstrate that he had learnt from experience of running a finger through a tablesaw blade. The big problem was the evidence clearly showed he had done it three different times!

 With health, the hazard or threat may not be obvious – we are totally unable to detect Gamma radiation and some sources of that are used in construction work and of sufficient power to provide a lethal dose quite quickly and with the individual not immediately knowing. Vibration is one we are all familiar with and yet this is often ignored. The 'perception' of hand-arm vibration is often that it is a minor issue, but the reality is that regular exposure to levels above the acceptable values can result in severe damage to blood vessels and nerves and the well-documented 'vibration white finger'. This can be so serious it is a recognised disability but as it takes time to develop and it seems innocuous as it does so, it is perceived as little or no threat. The last time you used an orbital sander and your fingers tingled after about 20 minutes – you were in the realms of tissue damage and adding to the eventual chance of a chronic disabling condition.

Reporting health and safety

The other problem with our two words is how they are reported. In 2013, there were 39 deaths in construction work and much is made of how dangerous this industry is, but in the same period around 100 times that number of deaths occurred from work-related disease and ill-health. It is estimated that around 500 die every year from exposure – over a period of time –  to silica dust. How many times have you seen workers engulfed in dust clouds? Because it isn't instant, we easily decide it is not a threat; thinking one-off working won't matter even if we have a coughing episode after stopping!

We are intending to now look at how people behave and why. One leading psychologist has spent years looking at this; James Reason first published Human Error in 1990 (Reason, 1990) and proposed that all failures to do what we might consider to be the 'right thing' are errors and these we can classify into four types:


A performed physical action goes wrong. You reach for the 'OFF' button on a saw but hit the start button with little adverse consequence so we probably ignore this obvious design flaw. You switch on mains power to a router and it starts as the machine switch is already 'ON' and if you are holding the router you may have a serious hand injury. Often these can be caused by poor design, which affects your appropriate performance. The latter example is also more likely to be due to a lapse.


A lapse of memory or attention – see above example. You are working on something and a distraction takes you away. When you recommence, you miss something out. For example, you are part way through changing a tablesaw blade when the phone rings. On return you finish replacing the table insert, refit the riving knife and guard and use the machine. You then find the blade is loose as you failed to fully tighten the arbor and check it. Distractions can play a significant part in lapse type errors but so can many other factors.


Not understanding how something works or an error of diagnosing or planning a work activity. Mistakes are defined (Reason 1990) as deficiencies or failures in the judgemental and/or inferential processes involved in the selection of an object or in the specification of the means to achieve it, irrespective of whether or not the actions directed by this decision-scheme run according to plan. It helps to understand these can be further defined as Rule-Based mistakes or RB, and Knowledge-Based mistakes or KB. We'll come back to these.


A deliberate breach of rules and procedures. Possibly the most common example is exceeding a speed limit in a road vehicle. This can be closely linked to perceptions. 17-year-old drivers have little real experience but often believe they are superior drivers with better control and handling skills than everyone else and driving fast is not a problem; they usually also fail to perceive correctly the reasons for any speed limit. The highest death rate in vehicle accidents is 17-24 year old males!

Types of errors

Another researcher Rasmussen (1986) had previously related three basic error types to three performance levels.

Performance level

1. Skill-Based level

2. Rule-Based level

3. Knowledge-Based level

Error type

1. Slips and lapses

2. Rule-Based mistakes

3. Knowledge-Based mistakes

With woodworking, great emphasis is placed on skills and if we remain at that level we predominantly suffer slips and lapses as manifestations of error. The RB and KB levels come into play after the individual has become conscious of a problem.

Rule-Based mistakes

With Rule-Based mistakes, the key assumption is that when confronted with a problem we are strongly biased to find a ready-made solution at the RB – or Rule-Based level. Rules are easier to learn and if we are given a good set of instructions – with demonstration – of how to use a guide-rail saw we can follow those happily. Should a situation arise outside of those instructions we may then move to an action also outside the RB level. We are using the saw to cut a 15mm strip from the edge of a plywood sheet and if the 'rules'.