Ever since there has been workers, employees, managers, and supervisors the question of why accidents happen has been pondered. If only there was a reason that could be understood, a root cause, corrective action could be taken. To help shed some light on this topic, we will look at the work of several great minds in the field of safety, and perhaps provide some insight on why accidents occur.

There are many reasons accidents occur, and many different opinions as well as suggested answers to the majority of causes. To begin determining what created an accident requires study of the events prior to and ending with the accident. This is referred to as Causal Analysis. In 2012 a safety professional by the name of Jeffrey Oakley, Ph.D., CSP described causal analysis as “a process in which the investigator analyzes, probes, discovers, ponders, and uses scenarios, facts, test, and assumptions to determine what caused an accident.” Having explained what type of investigations go into researching an accident cause, we can now begin by looking at the research of one of safety’s early pioneers.

In 1959, Henry Heinrich was a safety professional researching workplace accidents. He studied the 75,000 accident claims that occurred at Travelers Insurance company and discovered some remarkable information. 88% of these accidents were caused by unsafe acts, 10% were caused by unsafe conditions, and 2% were considered unavoidable. This information caused Heinrich to develop several different theories one accident causes with one of them being the Domino Theory of Accidents.

Heinrich suggested that there are five factors in the accident sequence. These five areas are Ancestry and Social Environment, Fault of the Person, Unsafe Act and/or Mechanical or Physical Hazard, Accident, and Injury. When one of these factors began to topple, it would impact the area next to it, creating a Domino Effect that would lead to an end result of an accident or injury. Here are some further explanations of each of these factors.

Ancestry and Social Environment: these are negative character traits that have the potential to cause people to perform an unsafe act, which can be obtained by inheritance or through the social environment.

Fault of Person: the inherited or acquired negative traits which cause the committing of unsafe acts or cause the existence of mechanical or physical hazards.

Unsafe Act and/or Mechanical or Physical Hazard: the unsafe performance of persons along with the mechanical or physical hazards of equipment that directly result in an accident.

Accident: events such as falling are being hit by moving objects that result in injury.

Injury: the injury that occurs from the accident such as a laceration, fracture, or death.

Heinrichs conclusions of the Domino Theory were that injuries are caused by the actions of preceding factors, and the removal of the central factor (unsafe acts or hazardous conditions) negates the action of the preceding factors and in doing so, prevents accidents and injuries from occurring.

Heinrich is also credited with creating the Iceberg of injury and illness, also known as the Hierarchy of Injuries. This illustration is of an iceberg floating in the ocean where only the top tip is visible above the waterline. The top tip is identified as Major Accident. This is obvious to everyone, but just below the waterline are 29 minor injuries that happened before the major accident occurred. Even below the minor injuries are 300 near misses that would have occurred, leading up to the 29 minor injuries. This is where Causal Analysis could probably identify an issue and stop the Major Injury from occurring by intervening at the Near Miss level.

In 2011, David Goetsch presented his Human Factors Theory for Human Errors. His idea is that Human Factor Errors can result in Overload, Inappropriate Activities, or Inappropriate Responses. These are defined as follows:

Overload: the imbalance between a person’s capacity at any given time and the load that person is carrying in a given state. Capacity is influenced by the person’s ability, training, state of mind, fatigue, stress, and physical condition. Loads are made up of various burdens including environmental factors, internal factors, situational factors, and more. Environmental factors, internal factors such as personal problems emotional stress, and situational factors such as unclear instructions and increased risk level all affect Overload.

Inappropriate response and incompatibility: how a person responds to the work experience or in a given situation can have a large effect on the outcome. When a person responds inappropriately, they fail to eliminate the hazardous condition and the risk of injuries increases. Detecting a hazard but not correcting it, removing safeguards, and ignoring safety also make up Inappropriate Response.

Inappropriate activities: underestimation of the degree of risk related to a task is an example of inappropriate activity that could lead to an accident or injury. Performing task without training and misjudging the degree of safety involved are impactors on Inappropriate Activities.


In 2010, Panagiotis Mitropoulos and Gerardo Cupido published an article in the Journal of Construction Engineering and Management outlining their analysis of residential framing accidents and task demands. Based on their studies they determined that the accident process has a sequence of factors that cause accidents. These factors are the existence of a hazard, exposure to the hazard, error or loss of control, and consequences.

They also developed a Prevention of Accidents plan. This plan outlined a strategy of accident prevention based on the reduction of hazards, reduction of exposure to the hazard, reduction of error or loss of control, and mitigation of consequences.


Rodney Grieve and Robert Greenwood, published a book on leadership essentials in 2008 titled SOAR. In this book they postulated that culturally introduced behaviors results in errors driven by the organizations culture, which is the ” that’s the way we do things around here” behavior. This cycle of logic, where at an organizational level relies on factors such as hard facts which are the top 10% of the company beliefs which are built on logical-rational conscious material and external facts and expertise. The cultural level makes up the soft facts and are the 90% of the cultural belief that make up emotional, unconscious, immaterial, internal emotions, and social skills of the company culture. Also added to this are other factors associated with accidents such as the employee behavior theory, drugs, alcohol, depression, obesity, management failure, and a host of other effectors.

So what do all of these studies tell us about accidents and their cause? Here are a few of pieces of information you can take from all of this work. Accidents can be caused by work system designs that create the opportunity to error. This is the work to be done, the location, the layout, the conditions, the tools, the equipment, the activities, and everything associated with work that increases or decreases the chances for error.

Culture plays a huge role in creating or preventing an accident. This is when we make assumptions about the external world that affects our “risk-taking” and causes the forming of strategies to engage that external world.

Training and early response to accident indicators such as near misses and minor accidents can disrupt the accident chain of events and prevent a serious or fatal accident from occurring.