Accident Causation Theory

Why Accidents Happen: The Theories of Causation

Whitney D. Gunter, M.S., C.P.O.

“They’re funny things, Accidents. You never have them till you’re having them.”

- Eeyore (from A. A. Milne’s Winnie The Pooh)

Accidents occur everyday and, one way or another, will impact virtually everyone.

During the year of 2005, there were approximately 4.2 million on-the-job nonfatal injuries in the

United States (Bureau of Labor Statistics, 2006). That same year, there were also 5,702 on-the-

job fatalities (Bureau of Labor Statistics, n.d.). Obviously, not all of these injuries are accidents

(e.g., workplace violence and other non-accidental injuries are included), but many of them are

accidents. Additionally, on-the-job accidents account for only a small portion of injuries and

fatalities following accidents. Further highlighting the impact of accidents is the costs absorbed

by organizations. Even when workman’s comp is not a factor, employers often absorb costs

relating to sick leave, health care and, of course, time and money spent investigating the

accident.

Even further expanding upon the impact of accidents is the great number of accidents that

do not result in injuries. In one of the earliest studies of accidents, H. W. Heinrich (1936) found

that for every serious injury, there were 29 minor injuries and 300 accidents resulting in close

calls. At that rate, even assuming that all injuries (major or otherwise) are included in the official

statistics, there would be an additional 42 million accidents that go unreported.

For the record, an accident is technically anything that happens by chance or misfortune.

This definition provides two important points. First, accidents are unavoidable as a whole; the

chance of one occurring will virtually always be present. Second, the chance of an accident

occurring is a variable that can be changed. While it is impossible to prevent all accidents, it is

possible to decrease their rate of occurrence. Understanding the cause of a phenomenon such as

this is key to decreasing its occurrences, as often knowing the cause is the only was to formulate

effective prevention strategies. Presented below are a few of the most common theories used to

explain accidents. As with theories discussed in other chapters, these are not perfect and will not

explain every accident in full detail. Rather, they provide a nomothetic explanation that seeks to

explain what usually happens and attempts to address the most common underlying causes.

Heinrich’s Domino Theory

As one could easily guess from the commonly used name for Heinrich’s theory, Heinrich

(1936) explained accidents using an analogy to dominos falling over one another and creating a

chain of events. While this theory is not the most advanced or complex theory, it is especially

noteworthy as one of the first scientific theories used to explain accidents. It is often still

referenced today, seven decades later.

When dominos fall over, each tips the next enough to push it over and continue the

process until all the connected dominos have fallen. However, if just a single domino is removed,

the entire process ceases. Heinrich explains accident causation in the same way:

Figure #1: Heinrich’s Domino Theory

As you can see from the figure, Heinrich identified five stages of accident causation. The

first stage, the social environment and ancestry, encompasses anything that may lead to

producing undesirable traits in people. More precisely, this includes the nature and nurture

aspects of someone’s background. Genetics, poor parenting/socializing, and an unhealthy

subculture are all examples of characteristics of nature and nurture that can negatively influence

individuals and lead to the next stage of accident causation. It is worth noting that Heinrich’s

inclusion of genetics and ancestry is very much a product of the time it was written. A

modernized version of this theory would likely use the term “inherited behavior,” similar to how

alcoholism and temperaments can be inherited. This stage of accident causation, especially the

parenting and subculture aspects, is quite similar to the social learning theories discussed in the

criminological theories chapter of this textbook.

The second stage, faults of a person, refers to personal characteristics that are conducive

to accidents. For example, having a bad temper may lead to spontaneous outbursts and disregard

for safety. Similarly, general recklessness can also be one of the manifestations of poor

character. Ignorance, such as not knowing safety regulations or standard operating procedures, is

also an example of this stage.

The third stage, an unsafe act or condition, is often the beginning of a specific incident.

Unlike the first two stages, which affect the probability of accidents occurring, this stage is

closer to the accident in terms of temporal proximity. This can include a specific act that is

unsafe, such as starting a machine without proper warning, or failing to perform appropriate

preventative actions, such as using guardrails or other safety measures. In essence, this stage

entails acts (or failures to act) that occasionally cause accidents.

The next stage, logically, is the accident itself. This, in and of itself, needs little

explanation. It is, simply, when something occurs that is undesirable and not intended. The final

stage, injury, is the unfortunate outcome of some accidents. Whether an injury occurs during an

accident is often a matter of chance and not always the outcome. This relationship highlights the

relationships between stages in terms of causality. An accident occurring is not a sufficient cause

for an injury, but it is a necessary one. Similarly, the undesirable characteristics in stage two do

not always occur in poor environments, but could not occur without such environments.

Given this necessary causality, the most important policy implication is to remove one of

the dominos (though try for more than one just to be safe); produce a healthy subculture through

positive accident prevention training and seminars, attempt to weed out people with undesirable

characteristics (or otherwise address said traits), and, if all else fails, have a procedure in place

for dealing with accidents to minimize injury and loss.

Ferrell’s Human Factor Model

Unlike Heinrich, who explained accidents with a single chain reaction in vague terms,

Ferrell’s model incorporates multiple causes and is very specific about these causes (Heinrich,

Petersen, & Roos, 1980). Additionally, Ferrell defines accidents in terms of being the result of an

error by an individual. As such, he explains his theory using the assumption that accidents are

caused by one person.

Ferrell identifies three general causes of accidents: overload, incompatibility and

improper activities. Each of these are actually broad categories that contain several more specific

causes. Improper activities is perhaps the simplest of the concepts, as it encompasses two

straightforward sources of accidents. First, it is possible that the responsible person simply didn’t

know any better. Alternatively, he or she may have known that an accident may result from an

action, but deliberately chose to take that risk. The incompatibility cause is slightly more

complex than improper activities. It encompasses both an incorrect response to a situation by an

individual, as well as subtle environmental characteristics, such as a work station that is

incorrectly sized.

The remaining cause, overload, is the most complex of Ferrell’s causes. It can further be

broken down into three subcategories. First, the emotional state of the individual accounts for

part of an overload. These states include conditions such as unmotivated and agitated. Second,

the capacity refers to the individual’s physical and educational background. Physical fitness,

training, and even genetics play a part of this. Situational factors, such as exposure to drugs and

pollutants, as well as job related stressors and pressures, also affect one’s capacity. Finally, the

load of the individual can also contribute to an overload. This includes the difficulty of the task,

the negative or positive effects of the environment (noise, distractions, etc.), and even the danger

level of the task. Separate from each other, overload, incompatibility, and improper activities can

all cause a human error to occur, which can lead to an accident.

Petersen’s Accident/Incident Model

Petersen’s model is largely an expansion upon Ferrell’s Human Factor Model (Heinrich,

Petersen, & Roos, 1980). The notion of an overload, caused by capacity, state or load, is very

similar to Ferrell’s work. However, a few changes and refinements do exist. First, Petersen

conceptualized the environmental aspect of incompatibility (work station design and

displays/controls) as a different part of the model, calling them ergonomic traps. Additionally,

Petersen also separated a decision to err from the overload cause. Further, Petersen also specified

separate reasons to choose to err. These reasons include: a logical decision due to the situation

(primarily for financial cost and temporal deadlines), an unconscious desire to err (psychological

failings), and perceived low probability of an accident occurring. The latter of those reasons, the

perception of low accident probability, can include both actual instances of an accident being

extremely unlikely, as well as the natural inclination of a human to disregard his or her own

mortality. This aspect of Petersen’s model is akin to criminology’s rational choice perspective

(see the criminological theories chapter), as it makes the same assumptions of human rationality

and hedonistic calculus.

Another noteworthy contribution is Petersen’s recognition that human error is only part

of a larger model. A system failure, the inability of the organization to correct errors, was added

as a possible mediator between errors and accidents. These failures have a range of possible

occurrences. The failure of management to detect mistakes and a lack of training are but two

examples of systems failures. Even poor policy itself can lead to a systems failure that does not

prevent an accident from occurring following a human error.

The Epidemiological Approach

Thus far, the chapter has focused on theories of accident causation. Each theory, while

perhaps built upon some anecdotal observations or one or two established relationships, is by

definition highly theoretical. In other words, each is one person’s best guess as to what is

occurring. The purpose is to explain some sort of correlation that have observed (statistically or

anecdotally). The epidemiological approach is different from these theories. Rather than take a

little data and try to formulate a theory, the epidemiological approach continually relies on

collecting additional information to expand our knowledge.

This technique can be observed in current insurance provider practices. For example, it

could be observed that a company in one particular profession is more likely to experience an

accident than the overall average. The insurance provider would then increase the insurance rates

for any organization partaking in the more dangerous profession. The same type of experience

could exist for a particular machine or even based on the geographic location. This can also show

us what decreases the likelihood of accidents. For example, an insurance provider might observe

that increased safety training programs are negatively correlated with accidents. Rates could be

then lowered for organizations using such programs or a discount used as an incentive to

increase training.

Systems Models

Most of the theories thus far discussed focus on human errors and environmental flaws. A

systems model theory approaches the relationship between persons and their environments

differently. Rather than the environment being full of hazards and a person being error prone, a

system model view sees a harmony between man, machine, and environment. Under normal

circumstances, the chances of an accident are very low. Once someone or something disrupts this

harmony by changing one of the components or the relationships between the three, the

probability of an accident occurring increases substantially.

Another aspect of the systems model is what is referred to as risk-taking. Whenever

someone chooses to do something, there is an associated risk (Firenze, 1978). Smaller tasks and

risks are often calculated on an unconscious level. For example, when one chooses to drive to

work each morning, that person weighs the risks (slight chance of being in a car accident) and

the benefits (making a living) and decides the benefits outweigh the risks. This hedonistic

calculus, as with Petersen’s model, is quite similar to the rational choice perspective. Just as

potential criminals may weigh the risks of being caught, managers, safety specialists and

supervisors consider the chances of injury or financial loss. The decision to move forward with

the task is only taken when it is decided the potential benefits outweigh the potential loss. In a

real life example of this type of risk taking behavior, Ford was once accused of deciding that the

risks of releasing a defective vehicle (several fatalities that would result in wrongful deaths) were

not enough to outweigh the benefit (not having to pay to fix all the defective vehicles). While

subsequent reports have shown that this accusation is false to a large extent (Schwartz, 1991),

this particular case has often been cited as an example of the ethical and financial calculations of

risk-taking.

Firenze (1978) suggests considering five calculated risks and benefits:

Figure #2: Firenze’s Five Calculated Risks and Benefits

1) Job requirements

2) The capabilities and limitations of the worker in

relation to her or her job

3) The potential gain upon succeeding

4) The potential consequences upon failure

5) The potential loss of not attempting the task

Additional information about these five factors becomes available through feedback after an

initial attempt. In other words, a common task previously taken has well known risks and

benefits, while a new task often has more unknown factors.

The Integration of Theories and General Program Implications

Much like other theories, each theory of accident causation does not explain every

accident. Rather, each explains one possible cause of an accident. For example, the

epidemiological approach fails to really explain why one thing causes an accident, just that it

does. Heinrich’s domino theory similarly fails to account for an environment, outside influences

or chance. Each theory explains only a portion of accidents and all of these theories are

incomplete. It is therefore important to recognize that true accident prevention, the reduction of

the probability of accidents, can only occur when all possible causes are addressed. Focusing on

only one or two theories is simply not enough. Further, there are numerous theories not even

briefly discussed in this chapter. Safety specialists and individuals with related duties are highly

encouraged to consult additional information about accident causation.

There are numerous program implications that can be derived even from the few theories

discussed in this chapter. Many of these are common sense, as they are often used practices.

First, most theories and models agree that human error is always a possible cause of accidents.

One of the simplest ways to address this is to avoid hiring accident-prone or shortsighted staff

and dismiss those that have shown carelessness. This, however, only addresses human error by

eliminating the extreme examples (people who show carelessness even before being hired) or

after an accident has already occurred. A more effective strategy is to train employees carefully.

Better safety training and increased knowledge of possible dangers can only decrease the chance

of an accident occurring.

Second, socialization and subculture are also a common thread in accident causation.

This further underscores the need for regular training and safety programs. A poor employee not

only increases the risk of causing an accident, he or she can also corrupt future staff and make

the problem grow exponentially. A safety awareness program is a good example of how to

approach this problem. Regular meetings and positive safety posters are some of the tactics an

awareness program can utilize. Keep employees motivated. The two-factor theory of motivation,

also called the Motivator-Hygiene theory (Herzberg, Mausner & Snyderman, 1959), suggests

that employees should be exposed to motivators (positive rewards) and hygiene factors (routine

parts of a job, such as a good working environment, that prevent dissatisfaction). Management,

whether involved in the awareness program or not, should also understand the importance of

maintaining a positive subculture and be trained with intervention strategies for problem

employees.

Third, the physical environment is also an important aspect of accident causation that

must be addressed. In addition to obvious implications (guard rails, safety warnings, hardhats,

etc.), the subtle relationships between man and machine must also be considered. Ergonomic

designs, often used to increase productivity, can also increase a worker’s comfort. Stress and

boredom can play a role in human error, so keeping agitators to a minimum through ergonomic

designs may also be helpful.

Finally, don’t rely solely on conventional thinking. Being proactive and using outside-

the-box thinking can further a safety program substantially. Offering incentives and rewards to

safety-oriented workers is a relatively new approach that, at minimum, gets attention. The status

quo can also be challenged by simply asking if more can be done. An important part of any

program is an evaluation to make sure it is working. Statistical analyses of accident rates,

surveys of individuals’ perceptions of safety and inspections by safety specialists are all

examples of potential indicators of program effectiveness. Triangulation (confirmation) of the

findings by using multiple indicators is important to validate findings. If possible, different

programs should be implemented within different environments so that effectiveness (or lack

thereof) can be compared. If a program is not working, ask how it could be better. If it is

working, ask the same.

Adapting Accident Causation to Specific Environments

Whenever a theory is developed for the social sciences, care must be taken to reinforce

the purpose of such a theory. Unlike theories in the natural and physical sciences, sociological,

business and economic theories are often developed with a nomothetic goal. That is, these

theories are created in an attempt to explain most situations most of the time. They can neither

account for all situations, as there will always be exceptions in the social sciences, nor can they

provide the specifics of an explanation. Rather, accident causation theories, like other theories,

are very general in nature. Developing specific policy implications from a general theory

requires additional knowledge about the specific environment to which the theory will be

applied. In other words, implications must be tailored to the needs and circumstances of an

environment.

The aviation industry provides an excellent example of how the general theories and

implications can be applied to specific industries. Here is primary concern of all accident

theories, implications and investigations is prevention (Wells, 1991). In addition to the obvious

risk to human life in the event of an accident, the industry also has a public image that affects

business to consider. One author observes, “accidents of the same type often require several

different preventative measures” (Wells, 1991, p. 83). Therefore, the goal of accident causation

theories and explanations in the aviation industry is to produce preventive measures even to the

point being overly redundant. For this specific environment, the need for excessive prevention

strategies outweighs the financial burden of such a tactic.

Industry specific views of causality are also a consideration in aviation safety. In

incident/accident investigations, the National Transportation Safety Board determines the causes

of an accident in terms of a chain of causality and typically allows up to and including five

specific causes in a single chain of events (Wells, 1991). This approach is quite similar to

Heinrich’s domino theory, yet is perhaps less specific about the nature of each domino. The

safety programs also provide some insight to the application of theory to practice. In addition to

the coordination efforts of air traffic safety and the high degree of training involved in flight, the

aviation industry also had strict maintenance practices to reduce accidents. As noted in multiple

theories, human error and machine failure are both potential causes of accidents.

In addition to the specific environment, one must also ask what type or types of accidents

need to be prevented. For example, fire safety is a type of accident prevention that must be

considered in virtually all environments. While the general theories of accident causation and the

general implications from the theories certainly apply, more specific knowledge about fires and

fire safety must also be considered. Most fire safety guidelines (e.g., Fiems & Hertig, 2001)

include a discussion of the fire tetrahedron and how removing one of the causes of fire (oxygen,

heat, fuel, or the chemical reaction) will prevent or stop a fire. This bears a striking resemblance

to Heinrich’s domino theory in which the prevention implication is to remove one of the

dominos of accident causation. This serves as an illustration of how general theories can be

applied to specific situations as well as specific environments.

The Future of Accidents and Accident Causation

Practical implications relating to accidents often have two parts. The main goal is

obviously to prevent accidents, but since accidents can never be completely prevented, a

secondary goal is to be prepared for the inevitable. On the reactive side of accidents, our path is

vague. In the aftermath of the terrorist attacks of September 11, 2001, interest in emergency

management has heightened. However, such interest has largely overlooked accidents, especially

small accidents, in favor of Terrorism and other malicious or intentional harm (Haddow &

Bullock, 2006). In the wake of Hurricane Katrina, the focus of emergency management has at

least partially included non-malicious events. Where does this leave the safety specialist

concerned with small accidents and workplace safety?

Despite the lack of interest by the public and the media, accident prevention continues to

be an important topic. Fiems and Hertig (2001) noted that fines by the Occupational Safety and

Heath Administration (OSHA) have been increased and more being imposed more liberally than

in years past for violations of unsafe working conditions. Additionally, more states are

legislating safety standards and security organizations are placing more emphasis on providing

both security and safety.

Since Heinrich’s Domino theory in 1936, knowledge about accident causation and its

counterpart, accident prevention, has grown remarkably. What once was the only theory

explaining accidents has served as the foundation of a discipline home to many theories,

perspectives and implications. This increase in knowledge, both among safety specialists and

other individuals, has a substantial impact on safety in the modern world. Together with

technological advances in safety and communication, accident causation theory and accident

prevention are more advanced than ever before. Understanding and quantifying causation will

lead us to a more scientific approach and cost-effective intervention strategies.

References

Bureau of Labor Statistics. (n.d.). Number of fatal work injuries, 1992-2005. Retrieved October

22, 2006, from: http://www.bls.gov/iif/oshwc/cfoi/cfch0004.pdf

Bureau of Labor Statistics. (2006). Workplace injuries and illnesses in 2005. Retrieved October

22, 2006, from: http://www.bls.gov/iif/oshwc/osh/os/osnr0025.txt

Fiems, R. A., and Hertig, C. A. (2001). Protection Office Guidebook. Naples, FL: International

Foundation for Protection Officers.

Firenze, R. J. (1978). The Process of Hazard Control. New York: Kendall/Hunt.

Haddow, G. D. and Bullock, J. A. (2006). Introduction to Emergency Management (2nd ed.).

Oxford: Butterworth-Heinemann.

Heinrich, H. W. (1936). Industrial Accident Prevention. New York: McGraw Hill.

Heinrich, H. W., Petersen, D., and Roos, N. (1980). Industrial Accident Prevention. New York:

McGraw-Hill.

Herzberg, F., Mausner, B., and Snyderman, B. B. (1959). The Motivation to Work. New York:

John Wiley.

Schwartz, G. T. (1991). The myth of the Ford Pinto case. Rutgers Law Review, 43, 1013-1068.

Wells, A. (1991). Commercial Aviation Safety. New York: McGraw Hill.

Quiz

1. For every serious injury, there are:

a) 9 minor injuries and 90 close calls

b) 29 minor injuries and 300 close calls

c) 299 minor injuries and 9,000 close calls

d) none of the above

2. Which of the following is not true of accidents in the U.S.?

a) There are around 4.2 million on-the-job nonfatal injuries each year

b) There are nearly 6,000 on-the-job fatalities each year

c) There are very few on-the-job accidents that could be prevented

d) There are potentially millions or billions more accidents that go unreported

3. According to Heinrich’s domino theory, which of the following is not a cause of accidents?

a) Faults of a person

b) The social environment

c) Sizable falling pillars

d) An unsafe act or condition

4. Which of the following identifies overload, incompatibility and improper activities as the

primary causes of accidents?

a) Heinrich’s domino theory

b) Ferrell’s Human Factor Model

c) Petersen’s Accident/Incident Model

d) The Epidemiological Approach

e) Systems Models

5. Which of the following acknowledges that an individual or organization might choose to err?





e) Systems Models

6. Which of the following suggests considerations for taking calculated risks?





e) Systems Models

7. Which of the following seeks to explain accidents solely through statistical inference?





e) Systems Models

8. True or false? Focusing on a single theory is sufficient for a safety specialist to find

implications.

9. Theories of accident causation can explain ____ situations ____ of the time.

a) all, all

b) all, most

c) most, all

d) most, most

10. True or false? Knowledge of the specific environment and specific types of accidents must be

applied to the theories to obtain meaningful implications.

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Accident Causation Theory