This is the second edition of Heinrich’s famous book, and from what I understand from the preface it has been reworked to a certain degree, yet I cannot say what the difference from the original is. Let’s go through the contents with some remarks underway:
Chapter 1 discusses Heinrich’s principles of accident prevention. One of his key themes is “hidden costs” of accidents that pop up already on page 2. The fundamental principles for accident prevention, according to Heinrich, are first listed 4 pages later: 1) creation and maintenance of active interest in safety (we could call this commitment, I guess), 2) fact finding, and 3) corrective action based on those facts. Quite common sense and we’re probably all in agreement. He goes on to discuss the fact that work on safety should be both top-down and bottom-up, but safety is mainly a management responsibility. Also Heinrich states that the work should be done methodically, based on scientific principles as he says, and not be dependent on “chance” - another recurring theme in the book.
The second chapter, “Basic Philosophy Of Accident Prevention”, represents more or less the heart of the book, with 60 pages it’s also the second longest chapter. Heinrich begins by listing his 10 Axioms Of Industrial Safety. According to him these are ‘self-evident truths’ which are explained in the course of the chapter. Some of these most of us will subscribe to; others will probably be rejected at first sight, so they’re probably not all that self-evident… Or at least not anymore.
The first axiom discusses the completed accident sequence, usually pictured by the famous domino sequence which we find for the first time on page 13. What struck me is that Heinrich did come up with the metaphor, but apparently not developed it to the point how we currently use it. Heinrich has very much focus on the human, the person at risk, the one bound to make a mistake and get hurt. Also in this early depiction of the accident dominos this tendency to look at the person comes through very clearly. Heinrich’s sequence is (from right to left): Injury - Accident - Unsafe Act - Fault of Person and Social Environment, the latter dealing very much with ancestry and accident proneness. That’s a rather far shot from the current sequence of (for example) Consequences - Accident - Direct Causes - Underlying Causes and Lack Of Control/Management Factors.
While Heinrich is pretty much focused on the person and thus often gets cited in connection with behaviour based safety, he doesn’t neglect the fact that good accident prevention means to remove dangerous situations (i.e. mainly technical measures) and another recurring theme is his focus on management (notably first line management and/or supervisors). On page 23 he even argues that while machines in themselves don’t make mistakes, preventive measures on them are more effective.
Pages 16 and 17 present another surprise (and a quite shocking one, with the benefit of 80 years hindsight) when Heinrich argues that one has to focus on the direct causes. In his view the unsafe act of a person is the most important in the action sequence and removing that will prevent the accident from happening. Heinrich does hint on underlying causes (he lists examples like training and supervision) but doesn’t call them that way yet (he will do this many pages further on).
This focus on direct causes is obviously quite in contrary to what contemporary safety science teaches: focus on the underlying causes is eminent; removing direct causes is little more than cleaning up the symptoms. And Heinrich seems to have understood this in a way, since he says on page 20 that “both kinds of causes should be eliminated as far as possible” (he talks here about human and technical causes, by the way), the example discussed on page 37 points towards a very diverse approach of accident prevention, and example 2 on page 38 is an excellent case of changing the environment that leads to changing the behaviour of persons. Still his continuous stress on unsafe acts and direct cause have certainly contributed to a great deal of misunderstanding of his work and led many a safety advisor and manager astray.
This misunderstanding is made even worse by the next theme Heinrich takes up: his (in)famous statement that 88% of all accidents are caused by unsafe acts. Of all the things Heinrich has written this bit is probably the item that has been taken out of context the most and twisted worst. If one takes just a little effort (really not much) one sees that 1) Heinrich talks about DIRECT causes here and 2) how he has found the 88%, which is rather arbitrary and not that much scientific at all. I have almost the feeling that Heinrich kind of fell in his own trap: he had the ambition to do something scientific and wanted to come up with a number, even if the way there wasn’t that scientific at all…
Page 27 pictures the other famous Heinrich metaphor: the triangle, pyramid or iceberg with a ratio between severe accidents and less serious incidents. He doesn’t call it this way, but he poses here the Common Cause Hypothesis (CCH), by stating that for every accident with consequences there are many other similar accidents without any consequences. This is another piece of work by Heinrich that has been bent, twisted and misunderstood in the course of the past decades. One, or maybe the, keyword in Heinrich’s statement is the fact that he talks about SIMILAR accidents. By keeping that in mind one will hardly proclaim that reducing minor incidents like slips, trips and falls will also reduce the number of major accidents like refinery explosions (see the Baker Panel report, the CSB Texas City investigation and everything on Deep Water Horizon).
It’s a sad thing that Heinrich’s brilliant idea of the CCH has been abused to so great extent that there are now even people who reject it all together - again without studying the initial proposal of the theory. And it has a lot going for it, doesn’t it. Heinrich makes a strong case by pointing out that the greater volume of minor incidents present an advantage to do something before a serious similar accident occurs. To quote the man (p. 30): “present day accident prevention is misdirected when it is based largely upon the analysis of major accidents” and (p. 32) “no accident, whether or not it results in an injury, is too insignificant to receive consideration…”. This was written more that 70 years ago and is still true today!
Heinrich does, by the way, a good job of separating consequences and the accident itself. For him it’s the potentiality that counts, i.e. he has focus on the risk. Oddly ‘risk’ is a word he hardly uses, if ever.
In connection with the pyramid one can say a few words on the 1 : 29 : 300 ratio that has become known as Heinrich’s Law among some. While Heinrich gets back to the ratio several times, he doesn’t appear to see this as a law himself. Even more, on page 30 he says that the number of no-injury accidents probably never will be known exactly! (By the way, on page 50 he has even a 1 : 82 : 2553 ratio…)
I talked already about causes. Heinrich is pretty much obsessed by those, even though a bit too much (for my and modern safety science’s taste) with direct causes. Another of his central messages is that causal analysis is necessary for the identification of countermeasures and accident prevention. On page 39/40 he for the first time poses the phenomenon of underlying reasons. A bit of a shame that he doesn’t expand his thoughts and theories on these.
In the final pages of chapter 2, Heinrich discusses a number of interesting thoughts that are highly relevant today:
- Safety and quality problems have the same causes and require the same actions (e.g. p.40).
- Safety is a management responsibility (p.43) with a special role for the foreman (see also appendix III).
- Accident prevention is good business (p.50, later also p.395) not at least because of the “hidden costs” for which Heinrich estimates a 1 : 4 ratio. On page 68 there is a strong paragraph that argues that safe factories tend also to be the more productive ones.
- The responsibility for the management is in Heinrich’s opinion rather a moral (p.43) or financial (p.50) one than that he says something about compliance (which appears to be the main driver for many a safety advisor these days).
Quite a lot of stuff for just one chapter…
Chapter 3 deals with creating and maintaining interest in safety. It contains a great deal of pseudo-psychology, but also contains a couple of sensible things (either supported by accepted theory or common sense), like the fact that one should think before doing and that it’s important to know your target group before acting. There are, however, also a few truly embarrassing and totally political incorrect and today unacceptable statements (like on immigrants, on p.75). Heinrich does mention a few useful angles for commitment raising campaigns, including (professional) pride as an important motivator.
The fourth chapter deals with Fact Finding. First Heinrich discusses the various causes: direct or proximate (acts and conditions), subcauses (personal factors) and underlying causes (managerial, supervision, social factors and environment). At this point I wonder why he never returned to his dominos and re-designed them with this distinction in mind. Others (e.g. Bird) would do this several years later… While Heinrich does mention underlying causes he regrettably chooses not to discuss these to any greater extend in his book. A missed opportunity, and as said before, a major source of misunderstandings afterwards and it weakens Heinrich’s work in retrospect because he keeps focusing on unsafe acts and direct causes (and measures to remove these). Even worse, in the next chapter (p.152) he even decreases the importance of underlying causes. A very strange argumentation.
On page 125 and 126 Heinrich poses a very strong statement for causal analysis as an essential element in improvement that is still valid today, and he says that if your causal analysis is good enough, you basically just need to “reverse” this cause to identify the remedy. At the end of the chapter he mentions that underlying causes may be the same for a larger number of different incidents. Without knowing it he hints here at the phenomenon of generic failure types and basic risk factors quite a few years ahead of Tripod and the like…
Chapter 5 deals with corrective action and accountability (especially for first line management) but leaves no further strong impression wasn’t it for one brilliant quote: “practicability and common sense must prevail in safety as in other things”. Sir, yes sir.
Chapter six is the book’s most extensive (nearly 100 pages) and for the greater part mainly of historical interest, dealing with the safeguarding of machinery and examples how to do this. The principles may still be valid today, but the machines discussed are out of use for many decades, I presume. A couple of interesting thoughts, however, also in this chapter:
- A nuance on his man-failure focus on p.168: it’s an important direct cause, but the environment has to be in good condition.
- Thus, the greatest safety gain and optimization is to be made in the design stage (p.169 and p.223/224).
- He introduces kind of a strategy for safety with taking on the source of danger as the first point of attack (p.170), this he will return to in the next chapter called Process and Procedure Revision with the central question: “why not do the job in another and better way”, again combining safety with efficiency and commercial gain.
- And, in a way he hints on RAMS on p.259: permanency, accessibility for repair, etc.
In the eighth chapter Heinrich takes on what he calls ‘safety psychology’. His definition of the word ‘psychology’ may clash with the understanding of many a current reader (including yours truly) and I can only say that Heinrich’s thoughts here are at least outdated. Various factors that Heinrich sees as reasons for accident proneness (and thus as psychological factors here) are definitely not (or at least not directly) psychology related: blood pressure, age, experience, skill.
The statement (p.269) that the safety rules should have “…enforcement no matter why not compliant…” is extremely dangerous and wrong. Of course it is of eminent importance to know why people are not compliant with safety procedures, how else can you help them to improve?!
Chapter 9 deals with fatigue. Most striking, and probably way ahead of his time, is here the observation that a machine should not dictate the tempo of the work. Also the remaining chapters are of lesser interest from today’s point of view, or rather specialist items like Chapter 11 on illumination. Heinrich does take on Occupational Diseases (10), First Aid (12), Accident Statistics (13, with too much space dedicated to a certain classification method, but good focus on registration of minor events - see p.344) and Education of Employees (14). The latter does include some interesting points, such as that safety education should be specific enough to make it relevant to the individual employee as well as another interesting quote (in my opinion against dumb compliance and for good leadership): “men go further when properly led than when driven”.
Chapter 15 contains a short summary in which Heinrich concludes that “action is the key”. Sounds good to me.
The book concludes with a bunch of appendices of which the first two are interesting from a historical point of view how safety has developed over the years. Other appendices do expand on a certain subject addressed in the main text, e.g. appendix III that discusses the role and responsibility of foremen and especially the urge to take that responsibility. Another slightly interesting one is appendix VIII that correlates age and accident injuries, showing that older/experienced workers have less injuries than younger colleagues, but that consequences on average are more severe. As far as I know an observation that is still valid (judging from some basic statistics during my years at the Haarlem workshop).
Details about the book:
Industrial Accident Prevention, H.W. Heinrich, 1941 (2nd edition), McGraw-Hill Book Company
To the next part of this article.