The Domino Theory
The following
famous quotation presages Heinrich’s Domino Theory, and explains it using a
different metaphor (horseshoe nails) than Heinrich (dominoes
falling over in a line).
"For the
want of a nail, the shoe was lost; for the want of a shoe the horse was lost;
and for the want of a horse the rider was lost, being overtaken and slain by
the enemy, all for the want of care about a horseshoe nail."
--Benjamin
Franklin, Poor Richard's Almanack
Herbert William
(“Bill”) Heinrich developed the Domino Theory while working at Travellers
Insurance Company in 1929, and expanded on it many times over many years. Heinrich spent quite a few pages elaborating
on the Domino Theory in the beginning of his famous book, Industrial
Accident Prevention, first published in 1931.
A Short Terminology Note for
Heinrich
You will notice
that during this section, when we are speaking directly about Heinrich and what
he said, we use the term “accident.”
Heinrich did not use the term “incident,” so when speaking of Heinrich
in specific, it’s more accurate. This
terminology also changes within the Domino Theory’s later incarnations, which
we will also discuss. Still, when we are
speaking in general, we will use the term “incident” as in the rest of this
course.
What Is The Domino Theory?
Heinrich’s Domino
Theory states that accidents result from a chain of sequential events,
metaphorically like a line of dominoes falling over. When one of the dominoes falls, it triggers
the next one, and the next…but removing a key factor (such as an unsafe condition or
an unsafe act) prevents the start of the chain reaction.
What are Unsafe Conditions and
Acts?
According to
Heinrich, all incidents directly relate to unsafe conditions and acts, which he
defines as “unsafe performance of persons, such as standing under suspended
loads ... horseplay, and removal of safeguards”; and “mechanical or physical
hazards such as unguarded gears ... and insufficient light.”
The Dominoes
Heinrich posits
five metaphorical dominoes labelled with accident causes. They are Social Environment and Ancestry,
Fault of Person, Unsafe Act or Mechanical or Physical Hazard (unsafe
condition), Accident, and Injury.
Heinrich defines each of these “dominoes” explicitly, and gives advice
on minimizing or eliminating their presence in the sequence.
1) Social Environment and Ancestry: This first domino in the sequence deals with
worker personality. Heinrich explains
that undesireable personality traits, such as stubbornness, greed, and recklessness
can be “passed along through inheritance” (12) or develop from a person’s
social environment, and that both inheritance and environment (what we usually
refer to now as “nature” and “nurture”) contribute to Faults of Person.
2) Fault of Person: The second domino also deals with worker
personality traits. Heinrich explains
that inborn or obtained character flaws (from 1) such as bad temper,
inconsiderateness, ignorance, and recklessness contribute at one remove
to accident causation. According to Heinrich,
natural or environmental flaws in the worker’s family or life cause these
secondary personal defects, which are themselves contributors to Unsafe Acts,
or the existence of Unsafe Conditions.
3) Unsafe Act and/or Unsafe Condition: The third domino deals with Heinrich’s direct
cause of incidents. As mentioned above,
Heinrich defines these factors as things like “starting machinery without
warning ... and abscence of rail guards.” (12)
Heinrich felt that unsafe acts and unsafe conditions were the central
factor in preventing incidents, and the easiest causation factor to remedy, a
process which he likened to lifting one of the dominoes out of the line. These combining factors (1, 2, and 3) cause
accidents.
Heinrich defines
four reasons why people commit unsafe acts – “improper attitude, lack of
knowledge or skill, physical unsuitability, [and] improper mechanical or
physical environment.” (36) He later
goes on to subdivide these categories into “direct” and “underlying”
causes. For example, he says, a worker
who commits an unsafe act may do so because he or she is not convinced that the
appropriate preventative measure is necessary, and because of inadequate
supervision. The former he classifies as
a direct cause, the latter as an underlying cause. This combination of multiple causes, he says,
create a systematic chain of events leading to an accident.
4) Accident: Of accidents, Heinrich says, “The occurrence
of a preventable injury is the natural culmination of a series of events or
circumstances which invariably occur in a fixed and logical order.”
(12-13) He defines accidents as, “events
such as falls of persons, striking of persons by flying objects are typical
accidents that cause injury.” (12)
5) Injury: Injury results from accidents, and some types
of injuries Heinrich specifies in his “Explanation of Factors” (12) are cuts
and broken bones.
To be fair to
Heinrich, he does insist that “the responsibility lies first of all with the
employer.” (38) (italics in original)
Heinrich specifies that a truly safety-conscious manager (of 1950) will
make sure his “foremen” and “workers” do as their told, and “exercise his
prerogative and obtain compliance ... follow through and see the unsafe
conditions are eliminated.” Heinrich’s
remedy for such non-compliance is strict supervision, remedial training, and
discipline.
The Life and Times of The Domino
Theory
By 1950, and the
fourth edition of Industrial Accident Prevention, Heinrich was still
promoting the same Domino Theory as in 1929.
By 1976, however, two scholars named Bird and Loftus were working with
Heinrich to update the Domino Theory.
By 1976, the
Domino Theory had been updated and changed slightly to reflect new developments
in safety theory, and a changing social and political climate. Bird and Loftus (along with input from
Heinrich) put forth this new revised version of the Domino Theory in their
well-known book Loss Control Management.
By 1994, the
Domino Theory was still in use, although it had changed dramatically from Heinrich’s
initial postulation. In his textbook Basic
Guide to Accident Investigation and Loss Control (1994), Jeffrey W. Vincoli
gives a detailed description of this updated Domino Theory, and even seems to
use its premises as the basis for the entire text.
By 1994, and
Vincoli’s book, the dominoes had been re-labelled and updated (with a new
emphasis on management, and incident as property loss), but the basic structure
and premises of the theory were still in place.
The revised model relabels the dominoes as Management: Loss of Control, Origins/Basic Causes,
Symptoms/Immediate Causes, Contact:
Incident, and Loss: People –
Property.
1) Management: Loss of Control: Vincoli says that “lack of control by
management” begins the process that eventually results in incidents. He stresses that if management do their job,
which he defines as “planning, organizing, leading, and controlling,” (16) they
can prevent incidents from happening at all.
If management does not do their job, however, it creates certain basic
causes from which incidents arise.
2) Origins:
Basic Causes: Vincoli
classifies these basic causes as belonging to two different groups: Personnel Factors, and Job Factors. Personnel Factors, he explains, reveal why
some people “engage in substandard practices (the third domino)” (or what
Heinrich called “unsafe acts”). Job
Factors reveal why “substandard conditions” (what Heinrich called “unsafe
conditions”) exist.
Personnel Factors
Lack of
understanding or ability
Improper motivation
(bad attitude)
Illness, mental,
or personal (non-work-related) problems
Note that these
factors are strikingly similar to, though expressed differently from Heinrich’s
“causes for unsafe acts of persons” (IAP, 36).
Job Factors
Inadequate work
Bad design or
maintenance
Low-quality
equipment
Normal or
abnormal wear and tear
3) Immediate Causes: Symptoms:
Vincoli brings in unsafe acts and conditions in Domino 3, just
like Heinrich. Unlike Heinrich
(directly), though, he says that unsafe acts and conditions are symptoms
of root causes that dominoes 1 and 2 represent. This approach is slightly different from
Heinrich, who seemed to feel the first two dominoes combine to produce the
third. Vincoli then goes on to say that
in an organizational environment where management allows these factors to
continue unchecked, incidents will occur.
4) Contact: Incident:
Vincoli defines incidents as any event which has the possibility of
creating a loss, and a loss event as an “accident.” (20) He also says that information-gathering (he
provides a list of incident types) helps create losses.
5) Loss:
People – Property: Using the
updated Domino Theory, Vincoli says that losses can’t be predicted, either in
how and when they will occur, nor in when.
Since his textbook is primarily on controlling loss, he provides several
remedies for directly dealing with incidents, mostly derived from Heinrich, and
rewritten.
The Persistence of the Domino
Theory
Such widely
dispersed dates (1929 – 1994) tell of the Domino Theory’s amazing
longevity. What makes the Domino Theory
so compelling as a causation model?
Likely, its popularity arises out of several reasons:
1) It’s simple. Many other causation models, such as
Multilinear Event Sequencing, are extremely complex and require the analyst to
practically have advanced engineering degrees.
(A short note on MES: As the Hitchhiker’s
Guide to the Galaxy says: Don’t
panic! All information presented on MES
in this course will be suitable for those without, because the author’s in the
same position.) The Domino Theory is
easy to use, assumes a logical, point-to-point view of causality and the world
at large, and doesn’t require the investigator to find many, many complicated
interrelating causes. It’s also easy for
non-safety people, such as management and workers, to understand. Nearly everyone has made lines with dominoes
and tipped them over, and nearly everyone likes problems that are easy to
understand and fix.
2) It’s an “easy fix.” According to the Domino Theory, if you want
to prevent incidents, just remove one of the (metaphorical) dominoes. Such simple solutions usually mean that
implementing recommendations generated by this model is no problem, and
everybody goes home at the end of the day feeling as though they’ve
accomplished something.
3) It places blame. Although one of the things this module
strives to teach is that blame is counterproductive, people generally have a
“scapegoating” tendency (“find the person responsible and punish them”). Determining who is responsible, and who will
take the blame (and the punishment) can feel very good to people who have been
hurt (through injury, grief, lost profits, etc.) and who may have a conscious
or unconscious desire for revenge.
4) It makes those who use it look good.
If an investigator can announce that he or she has “solved” the incident, and
knows which one thing or few things to fix in order to prevent the incident
from recurring, he or she can improve his or her professional image in a hurry.
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